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1
Krishtopenko, Sergey. "Spin splitting and collective effects in InAs/AlSb quantum well heterostructures." Toulouse 3, 2011. http://thesesups.ups-tlse.fr/1459/.
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Les travaux de cette thèse, essentiellement théorique, concernent l'étude des phénomènes dépendants du spin, à un électron et à n-corps, dans les puits quantiques (PQ) de semiconducteurs (SC) à faible gap InAs/AlSb. Les résultats obtenus permettent de prévoir de nouveaux effets physiques, ils sont comparés aux résultats expérimentaux existants. L'asymétrie du champ électrique aux interfaces InAs/AlSb est étudiée expérimentalement et théoriquement, son effet sur le spectre d'énergie des sous bandes électriques est mis en évidence. La possibilité de contrôler optiquement ce champ électrique, et par là le clivage de spin par effet Rashba sous champ magnétique nul, est démontrée. La prise en compte des interactions e-e sur les niveaux de Landau des quasi-particules ainsi que sur la densité d'états au niveau de Fermi est réalisée dans ce système pour la première fois. Le calcul théorique de l'exaltation du facteur g par échange dans les puits quantiques à faible gap est développé. Le calcul permet de prédire l'évolution du facteur g "magnéto-optique" dans les hétérostructures InAs/AlSb déterminé par résonance de spin, il met en évidence la violation du théorème de Larmor dans les hétérostructures à base de SC à faible gap. L'étude théorique de la résonance cyclotron, en régime quantique, d'un gaz bidimensionnel d'électrons de haute mobilité démontre aussi la violation du théorème de Kohn dans les hétérostructures InAs/AlSb. Les résultats obtenus dans ce travail de thèse apportent des informations utiles pour le "design" et la mise au point de nouveaux dispositifs électroniques ou optoélectroniques basés sur des hétérostructures InAs/AlSbThe Thesis is devoted to the study of "single-particle" and "many-body" spin-related phenomena in narrow-gap InAs/AlSb quantum well (QW) heterostructures. The scientific significance of the results obtained consists in the discovering and prediction of new physical effects. The asymmetry of the built-in electric field in InAs/AlSb QW heterostructures has been probed both experimentally and theoretically and its effect on the electron energy spectrum splitting in electric subbands is demonstrated. A principle possibility to control by optical means the "built-in" electric field and the Rashba spin splitting in zero magnetic field is exhibited. The theoretical investigation into e-e interaction effect on quasiparticle Landau levels and density-of-states at the Fermi level is undertaken for the first time. Theory of the exchange enhancement of quasiparticle g-factor in narrow gap QW heterostructures is developed in the Thesis. Calculation results on the "magnetooptical" g-factor in InAs/AlSb heterostructure measured in electron spin resonance are the first demonstration of Larmor theorem violation in narrow gap QW heterostructures. Cyclotron resonance study in the samples with high mobility 2D electron gas in quantizing magnetic fields provides evidences of Kohn theorem violation in InAs/AlSb heterostructures. The results obtained in the Thesis can be utilized at the designing new electronic and optoelectronic units as well the spintronic devices based on InAs/AlSb heterostructures
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COLOMBO, GIULIO. "GLOBAL GRADIENT BOUNDS FOR SOLUTIONS OF PRESCRIBED MEAN CURVATURE EQUATIONS ON RIEMANNIAN MANIFOLDS." Doctoral thesis, Università degli Studi di Milano, 2021. http://hdl.handle.net/2434/813095.
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This thesis is concerned with the study of qualitative properties of solutions of the minimal surface equation and of a class of prescribed mean curvature equations on complete Riemannian manifolds. We derive global gradient bounds for non-negative solutions of such equations on manifolds satisfying a uniform Ricci lower bound and we obtain Liouville-type theorems and other rigidity results on Riemannian manifolds with non-negative Ricci curvature.
The proof of the aforementioned global gradient bounds for non-negative solutions u is based on the application of the maximum principle to an elliptic differential inequality satisfied by a suitable auxiliary function z=f(u,|Du|), in the spirit of Bernstein’s method of a priori estimates for nonlinear PDEs and of Yau’s proof of global gradient bounds for harmonic functions on complete Riemannian manifolds. The particular choice of the auxiliary function z parallels the one in Korevaar’s proof of a priori gradient estimates for the prescribed mean curvature equation in Euclidean space.
The rigidity results obtained in the last part of the thesis include a Liouville theorem for positive solutions of the minimal surface equation on complete Riemannian manifolds with non-negative Ricci curvature, a splitting theorem for complete parabolic manifolds of non-negative sectional curvature supporting non-constant solutions with linear growth of the minimal surface equation, and a splitting theorem for domains of complete parabolic manifolds with non-negative Ricci curvature supporting non-constant solutions of overdetermined problems involving the mean curvature operator.
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Batista, Alex de Moura. "Sobre um Sistema do tipo Schrödinger-Poisson." Universidade Federal da Paraíba, 2012. http://tede.biblioteca.ufpb.br:8080/handle/tede/7369.
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In this dissertation, we study the existence of two types of non-negative weak solutions for a class of problems of Schrodinger-Poisson type. This kind of problem models, for example, several physical phenomena in quantum mechanics. Initially, by minimization arguments, Splitting Lemma and the Variational Principle of Ekeland we find a weak solution that minimizes the minimum energy level associated to the variety of Nehari N. This is the so-called ground state solution. Afterwards we will find, by using the Linking Theorem, a strictly positive weak solution which is not a ground state solution: the so-called bound state solution.
Nesta dissertação, estudaremos a existência de dois tipos de soluções fracas não negativas para uma classe de problemas do tipo Schrödinger-Poisson, os quais modelam fenômenos físicos, por exemplo, em Mecânica Quântica. Inicialmente, encontraremos através de argumentos de minimização, do Lema Splitting e do Princípio Variacional de Ekeland, uma solução fraca que minimiza o nível de energia mínima associado a variedade de Nehari N. Tal solução é denominada do tipo ground state. Em seguida, encontraremos através do Teorema de Linking, uma solução fraca estritamente positiva que não é do tipo ground state. Tal solução é denominada do tipo bound state.
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吳潔貞 and Kit-ching Betty Ng. "Correlation effects in crystal field splitting." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31230714.
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Ng, Kit-ching Betty. "Correlation effects in crystal field splitting /." [Hong Kong : University of Hong Kong], 1986. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12323342.
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Cavalcante, Marcius Petrúcio de Almeida. "Teorema de Decomposição de Cheeger-Gromoll." Universidade Federal de Alagoas, 2007. http://repositorio.ufal.br/handle/riufal/1020.
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We demonstrate the Splitting Theorem due to Cheeger and
Gromoll, which ensures that a complete Riemannian n-manifold
which has nonnegative Ricci curvature and a line, can be split
isometrically into the Riemannian product of real with a (n-1 )-
manifold.Conselho Nacional de Desenvolvimento Científico e Tecnológico
Demonstramos o Teorema de Decomposição de Cheeger-Gromoll, o qual garante que uma variedade Riemanniana completa ndimensional, com curvatura de Ricci não-negativa, que possui uma linha, pode ser decomposta isometricamente num produto Riemanniano de uma variedade (n-1 )-dimensional com o conjunto dos reais.
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Ura, Hiroyuki. "Multiple feature-checking : a theory of grammatical function splitting." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11238.
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Li, Xinxin. "Some operator splitting methods for convex optimization." HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/43.
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Many applications arising in various areas can be well modeled as convex optimization models with separable objective functions and linear coupling constraints. Such areas include signal processing, image processing, statistical learning, wireless networks, etc. If these well-structured convex models are treated as generic models and their separable structures are ignored in algorithmic design, then it is hard to effectively exploit the favorable properties that the objective functions possibly have. Therefore, some operator splitting methods have regained much attention from different areas for solving convex optimization models with separable structures in different contexts. In this thesis, some new operator splitting methods are proposed for convex optimiza- tion models with separable structures. We first propose combining the alternating direction method of multiplier with the logarithmic-quadratic proximal regulariza- tion for a separable monotone variational inequality with positive orthant constraints and propose a new operator splitting method. Then, we propose a proximal version of the strictly contractive Peaceman-Rachford splitting method, which was recently proposed for the convex minimization model with linear constraints and an objective function in form of the sum of two functions without coupled variables. After that, an operator splitting method suitable for parallel computation is proposed for a convex model whose objective function is the sum of three functions. For the new algorithms, we establish their convergence and estimate their convergence rates measured by the iteration complexity. We also apply the new algorithms to solve some applications arising in the image processing area; and report some preliminary numerical results. Last, we will discuss a particular video processing application and propose a series of new models for background extraction in different scenarios; to which some of the new methods are applicable. Keywords: Convex optimization, Operator splitting method, Alternating direction method of multipliers, Peaceman-Rachford splitting method, Image processing
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Dierolf, Bernhard [Verfasser], and Leonhard [Akademischer Betreuer] Frerick. "Splitting theory for PLH spaces / Bernhard Dierolf ; Betreuer: Leonhard Frerick." Trier : Universität Trier, 2014. http://d-nb.info/1197700307/34.
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Seidel, Markus. "Über die Splitting-Eigenschaft der Approximationszahlen von Matrix-Folgen: l1-Theorie." Master's thesis, Universitätsbibliothek Chemnitz, 2007. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200700129.
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In dieser Arbeit wird das asymptotische Verhalten der Approximationszahlen für Operatorfolgen aus einer speziellen Klasse von Banachalgebren untersucht. Es werden bemerkenswerte Eigenschaften der Folgen und der Approximationszahlen ihrer Operatoren gezeigt, darunter die so genannte splitting-Eigenschaft.
Ein typisches Beispiel solcher Operatorfolgen stellen die Finite Sections von Toeplitzoperatoren dar, die exemplarisch behandelt werden. Dabei werden hier auch die Folgenräume l1 und l-unendlich betrachtet.
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Li, Xiangyang. "Shear-wave splitting in reflection surveys : theory, methods and case studies." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/12418.
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Over the last decade, the use of multi-component seismic reflection data to study shear-wave splitting has become increasingly common within the hydrocarbon industry to determine the crack geometry of oil reservoirs. Thus, it is important to investigate the characteristics of, develop processing techniques for, and carry out case studies of shear-wave splitting in reflection surveys. I have examined the effects of anisotropic symmetry, particularly orthorhombic symmetry, on velocity variations and moveouts of split shear-waves in vertical off-symmetry planes. I have also examined the effects of crack orientation changing with depth on reflection and transmission coefficients of split shear-waves. These theoretical developments in understanding shear-wave splitting in reflection surveys are described in Chapters 2 and 3. Complex component analysis was developed as an alternative to polarization analysis for displaying and identifying shear-wave splitting in large seismic datasets. This complex component analysis allows the calculation of instantaneous amplitudes and instantaneous polarizations for two-component seismic data and of shear-wave splitting sections and polarization logs for four-component data. Four field seismic datasets, including a two- and a four-component VSP, a reflection shot data matrix and a two-component crosshole survey, have been used to verify and illustrate the technique, as described in Chapters 4 and 5. A linear-transform technique was developed as an alternative to rotation analysis for quantifying and processing shear-wave splitting in seismic data. This linear-transform technique allows various attributes to be measured, including the polarizations and time delays of split shear-waves and downhole geophone orientation. It also allows time series of the split shear-waves to be separated deterministically and such separation can be made before stacking in reflection surveys. Three field datasets including a zero-offset VSP, an offset VSP and a reflection shot data matrix, have been used to verify and illustrate the technique, as described in Chapter 6.
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Richardson, Jeremy O. "Ring-polymer approaches to instanton theory." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/243641.
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Inspired by the success of the ring-polymer molecular dynamics (RPMD) method, we derive a transition-state-theory version (RPTST) with a dividing surface which is, in general, conical in ring-polymer space. It is explained why this conical form is a good approximation to the optimal dividing surface and therefore why centroid-based quantum transition-state theories are inaccurate for asymmetric barriers at low temperatures. The geometry of the ring-polymer transition state is found to describe a finite-difference approximation to the semi-classical instanton trajectory (a classical periodic orbit of length βħ on the inverted potential). Based on this, a new practical method for locating multidimensional instantons is proposed, by computing saddle points on the ring-polymer surface, and a derivation for the reaction rate constant based on the "ImF" premise using the ring-polymer formalism is shown to be far simpler than in previous instanton approaches based on functional determinants. The resulting expression is based only on the ring-polymer potential at the transition-state and its Hessian, and is applied to evaluate the rate in a number of polyatomic systems. We show that a free-energy version of the ImF instanton theory is related to RPTST and thereby provide an explanation for why RPMD produces accurate results for thermal reaction rates in the deep-tunnelling regime and demonstrate how it can be made more efficient and systematically improved. From this, we also explain why RPMD is seen to underestimate the rates of symmetric reactions and overestimate the rates of asymmetric reactions. We also present a ring-polymer instanton derivation of a theory for calculating tunnelling splittings leading to another new practical method, which owing to its simple form, is easily extended to determine the entire tunnelling-splitting pattern of molecular clusters with two or more degenerate wells. This method is applied to the water dimer, trimer, and octamer, and shown to be in good overall agreement with experiment and to provide a deeper understanding of the tunnelling pathways.
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Seidel, Markus Silbermann Bernd. "Über die Splitting-Eigenschaft der Approximationszahlen von Matrix-Folgen : l1-Theorie$nElektronische Ressource /." [S.l. : s.n.], 2006.
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Reid, Adam. "Quantum tunnelling splittings in water clusters, from ring-polymer instanton theory." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709028.
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Gibson, Gregory Thomas. "Fundamental studies of electrocatalytic ozone generation via water splitting using density functional theory calculations." Thesis, Queen's University Belfast, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.726354.
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The work presented herein focuses on the widely studied water splitting mechanism forming ozone as the major product through an electrochemical process. Through the use of Density Functional Theory calculations the thesis highlights different catalysts in the literature, namely the beta-PbO2 and Ni/Sb-SnO2 systems, paying particular attention to the modelling of each catalyst and subsequently in determining the favoured mechanism for ozone formation on each catalyst. In addition to this, stability studies were carried out to further probe the surface chemistry, specifically through the addition of gold, as a means to better understand the thermodynamics of the systems in question.
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Park, Kyoung-Won. "Solar-driven overall water splitting on CoO nanoparticles : first-principles density functional theory studies." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/117802.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged student-submitted from PDF version of thesis.
Includes bibliographical references (pages 143-157).
Photoelectrochemical (PEC) water splitting has been suggested as a promising techinique for large-scale hydrogen fuel production. In particular, spontaneous photocatalytic overall water splitting on self-standing particles in water without external driving potential has been highlighted as a clean and economical energy generation method for the future. Among various photocatalytic materials, some cobalt-based materials including CoP, Co₂P, Co(OH)₂, CoO, have attained major interest because they exhibit improved catalytic activity for hydrogen evolution in the form of nanoparticles, unlike most cobalt-based materials which have been assessed as water oxidizing catalysts in the past decade. CoO nanoparticles have been observed to photocatalytically split water into H₂ and O₂ at room temperature without an externally applied potential or co-catalyst, with high photo-catalytic efficiency (solar-to-hydrogen efficiency of ~5%) which hits the record among single-material self-standing photocatalysts. The photocatalytic activity of CoO nanoparticles was experimentally shown to stem from the optimal conduction and valence band edge positions (Ec and Ev) relative to water reduction and oxidation potential levels (H+/H₂ and H₂O/O₂), such that the Ec and EV span the water redox potentials. The overall water splitting is not expected from CoO micropowder or bulk CoO because they have band edges far below the H+/H2 level, which are not optimal for overall water splitting. However, the origin of the shift in the band edges due to decrease in particle size (from bulk or micropowder to nanoparticle) was unknown. Moreover, the mechanism by which H₂ and O₂ simultaneously and spontaneously evolve on the nanoparticles, as well as how the CoO nanoparticles could exhibit a high photocatalytic efficiency even without a co-catalyst or an external driving potential have remained unanswered. In this work, we use first-principles density functional theory (DFT) calculations to explore thermodynamically stable surface configurations of CoO in an aqueous environment in which photocatalytic water splitting occurs. We also calculate the Ec and Ev of CoO surfaces relative to water redox potentials, showing that the band edge positions are sensitive to surface chemistry which is determined by surface orientation, adsorbates, and stoichiometry, and thus growth conditions and operating environment. In particular, we predict that CoO nanoparticles have fully hydroxylated CoO(111) facets (OH*-CoO(111)), with band edges spanning the water redox potentials, while larger CoO particles (such as CoO micropowders) have a full monolayer of hydrogen on the CoO(111) facets, with a band alignment that favors water oxidation but not water reduction. From these calculations, we demonstrate that explicit inclusion of liquid water is crucial for accurately predicting the band edge positions, and thus photocatalytic behavior of CoO in an aqueous solution. In order to find the origin of the high efficiency and spontaneous overall water splitting without an external bias or a co-catalyst, we also elucidate the mechanisms for charge separation and H₂ and O₂ evolution on CoO nanoparticles under illumination in an aqueous solution. We demonstrate that electrons are driven to CoO(100) facets and holes are driven to OH*-CoO(111) facets as a result of a built-in potential arising from the very different potential levels of the two facets. We show that H₂ evolution preferentially occurs on the CoO(100) facets, while O2 evolves on the OH*-CoO(111) surfaces, based on our new criteria. Importantly, we suggest that the conventional criterion for determining the feasibility of H₂ or O₂ generation from water splitting - i.e., EC < H+/H₂ level or Ev > H₂O/O₂ level - is insufficient. Instead, we suggest that a more appropriate set of criteria is whether the photo-excited electrons and holes have sufficient energy to overcome the kinetic barrier for the H₂ and O₂ evolution reaction, respectively, on the relevant surface facet. This work explains why and how photocatalytic overall water splitting has been observed only on CoO nanoparticles. Our understanding of the overall water splitting mechanism on CoO nanoparticles provides a general explanation of experimentally observed overall water splitting phenomena on a variety of self-standing photocatalysts as well as a new approach for screening novel photocatalytic materials for efficient water splitting and other reactions.
by Kyoung-Won Park.
Ph. D.
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Cao, Kanyu. "Crystal-field splitting of Er 3+in ZnO and experimental observations." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177608455.
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Hewa, Dewage Amendra Fernando. "Theoretical investigation of the water splitting mechanism on transition metal oxide catalysts." Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32148.
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Doctor of PhilosophyDepartment of Chemistry
Christine M. Aikens
Water oxidation can be considered as the ‘holy grail’ of renewable energy research, where water is split into constituent molecular hydrogen and oxygen. Hydrogen is a very efficient energy source that is both clean and sustainable. The byproduct of hydrogen combustion is water, which in turn can be reused as the source for hydrogen generation. Natural water splitting is observed during photosynthesis in the oxygen-evolving complex of photosystem II, which consists of a CaMn₄O₄ cubane core. Herein, we report in silico approaches to understand bottom up catalytic design of model transition metal oxide complexes for water splitting. We have employed density functional theory to investigate model ligand-free architectures of cobalt and manganese oxide dimer (Mn₂(μ-OH)(μ-O)(H₂O)₃(OH)₅, Mn₂(μ-OH)₂(H₂O)₄(OH)₄, Mn₂(μ-OH)₂(H₂O)₂(OH)₂(O(CH)₃O)₂, Co₂(μ-OH)₂(H₂O)₄(OH)₄ and cubane (Co₄O₄(H₂O)₈(OH)₄, Mn₄O₄(H₂O)[subscript]x(OH)[subscript]y x = 4-8, y = 8-4) complexes. The thermodynamically lowest energy pathway on the cobalt dimer catalyst proceeds through a nucleophilic attack of a solvent water molecule to a Co(V)-O radical moiety whereas the pathway on the cubane catalyst involves a geminal coupling of a Co(V)-O radical oxo group with bridging oxo sites. The lowest energy pathway for the fully saturated Mn₂O₄•6H₂O (Mn₂(μ-OH)(μ-O)(H₂O)₃(OH)₅) and Mn₂O₃•7H₂O (Mn₂(μ-OH)₂(H₂O)₄(OH)₄) complexes occur through a nucleophilic attack of a solvent water molecule to Mn(IV½)O and Mn(V)O oxo moieties respectively. Out of all the oxidation state configurations studied for the manganese cubane, we observed that Mn₄(IV IV IV IV), Mn₄(III IV IV IV), and Mn₄(III III IV V) configurations are thermodynamically viable for water oxidation. All three of these reaction pathways proceed via nucleophilic attack of solvent water molecule to the manganese oxo species. The highest thermodynamic energy step in manganese dimer and cubane complexes corresponds to the formation of the manganese oxo species, which is a significant feature that reoccurred in all these reaction pathways. We have also employed multireference and multiconfigurational calculations to investigate the Mn₂(μ-OH)₂(H₂O)₂(OH)₂(O(CH)₃O)₂ system. The presence of Mn(IV)O[superscript]• radical moieties has been observed in this catalytic pathway. These simplest models of cobalt and manganese with water-derived ligands are essential to understand microscopic properties that can be used as descriptors in designing future catalysts.
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Sieg, Dennis [Verfasser], and Leonhard [Akademischer Betreuer] Frerick. "A Homological Approach to the Splitting Theory of PLS-spaces / Dennis Sieg ; Betreuer: Leonhard Frerick." Trier : Universität Trier, 2010. http://d-nb.info/1197696350/34.
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Kelly, Martin. "The role of lattice vibrations in the zero field splitting of Gd'3'+ in an ethylsulphate host lattice." Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357631.
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Morales, Herbert. "BOSONIZATION VS. SUPERSYMMETRY." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/429.
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We study the conjectured equivalence between the O(3) Gross-Neveu model and the supersymmetric sine-Gordon model under a naive application of the bosonization rules. We start with a review of the equivalence between sine-Gordon model and the massive Thirring model. We study the models by perturbation theory and then determine the equivalence. We find that the dependence of the identifications on the couplings can change according to the definition of the vector current. With the operator identifications of the special case corresponding to a free fermionic theory, known as the bosonization rules, we describe the equivalence between the massless Thirring model and the model of a compactified free boson field. For the massless Thirring model, or equivalently the O(2) Gross-Neveu model, we study the conservation laws for the vector current and the axial current by employing a generalized point-splitting method which allows a one-parameter family of definitions of the vector current. With this parameter, we can make contact with different approaches that can be found in the literature; these approaches differ mainly because of the specific definition of the current that was used. We also find the Sugawara form of the stress-energy tensor and its commutation relations. Further, we rewrite the identifications between sine-Gordon and Thirring models in our generalized framework. For the O(3) Gross-Neveu model, we extend our point-splitting method to determine the exact expression for the supercurrent. Using this current, we compute the superalgebra which determines three quantum components of the stress-energy tensor. With an Ansatz for the undetermined component, we find the trace anomaly and the first beta-function coefficient. The central charge which can be computed without using our point-splitting method is independent of the coupling constant, in fact, it is always zero. For the supersymmetric sine-Gordon model, we review its supersymmetry in the context of models derived from a scalar multiplet in two dimensions. We then obtain the central charge and discover an extra term that was missing in the original derivation. We also analyze how normal ordering modifies the central charge. Finally, we discuss the conjectured equivalence of the O(3) Gross-Neveu model and the supersymmetric sine-Gordon model under the naive application of the bosonization rules. Comparing our results of the central charges and the supercurrents for these models, we find that they disagree; consequently the models should be generically inequivalent. We also conclude that the naive application of the bosonization rules at the Lagrangian level does not always lead to an equivalent theory.
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Hank, Georg E. "Steel meets leather - 259: The influence of cutting parameters in the leather splitting process." Verein für Gerberei-Chemie und -Technik e. V, 2019. https://slub.qucosa.de/id/qucosa%3A34203.
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Content:
This article wants to combine two perspectives: First, Leather production, focused on the splitting process, with its diverse quality requirements and second, the new evolutions in the field of bandknife properties.
In a short introduction the splitting process as such will be described, its different use in several stages and leather types, also in the field of leather conversion (in shoe, leathergoods and automotive parts production). Influencing factors of the possible goals like quality and cost efficiency will be discussed.
In the second part some main requirements and problem fields of leather splitting are analyzed in more detail.
Requirements such as thickness tolerance, tensile strength, flexibility, fibre-free smooth cutting surface. Difficulties in practice like chrome nests, hard water, poor raw material, feeding speed, influence of
abrasivity of leather.
In a third part the physics of the cutting process as such will be described. Explanation of basic terms as “cutting ability”, “edge retention”, “pull vs. press cut”. Resulting from this we get important parameters that refer to the bandknife blade: e.g. steel characteristics (hardness, flexibility, grindeability, microstructure at cutting point, geometry of knife bevels, weldability etc.). The possibilities in modern
bandknife production will be shown as for example: CNC-sensor-based tolerance measurements, presharpening, surface roughness variations. This is completed with a short view on the other components of
the process like splitting machine (points like sharpness measuring), grinding stones (roughness-exactness controversy diagram).
The fourth and last part puts the two perspectives together: Optimized bandknife characteristics for specific leather material. Alternative steel types that due to new properties allow to meet also new
requirements.
Take-Away:
Optimization of the splitting process
Better understanding of the bandknife properties
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Overstreet, Laura Carter. "Splitting Sexuality and Disability: A Content Analysis and Case Study of Internet Pornography featuring a Female Wheelchair User." unrestricted, 2008. http://etd.gsu.edu/theses/available/etd-11152008-193815/.
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Thesis (M.A.)--Georgia State University, 2008.Title from file title page. Elisabeth Sheff, committee chair; Dawn Baunach, Wendy Simonds, committee members. Description based on contents viewed Sept. 1, 2009. Includes bibliographical references (p. 54-56).
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Schober, Giulio Albert Heinrich [Verfasser], and Manfred [Akademischer Betreuer] Salmhofer. "Quantum Field Theory of Material Properties: Its Application to Models of Rashba Spin Splitting / Giulio Albert Heinrich Schober ; Betreuer: Manfred Salmhofer." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180738195/34.
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Yu, Qingzhao. "Bayesian synthesis." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1155324080.
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Gong, Wei 1981. "Theoretical investigations of terascale physics." Thesis, University of Oregon, 2009. http://hdl.handle.net/1794/10339.
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xv, 177 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.In this dissertation, three different topics related to terascale physics are explored. First, a new method is suggested to match next-to-leading order (NLO) scattering matrix elements with parton showers. This method is based on the original approach which adds primary parton splittings in Born-level Feynman graphs in order to remove several types of infrared divergent subtractions from the NLO calculation. The original splitting functions are modified so that parton showering has a less severe effect on the jet structure of the generated events. We also examine the Large Hadron Collider phenomenology of quantum black holes in models of TeV scale gravity. Based on a few minimal assumptions, such as the conservation of color charges, interesting signatures are identified that should be readily visible above the Standard Model background. The detailed phenomenology depends heavily on whether one requires a Lorentz invariant, low-energy effective field theory description of black hole processes. Finally, in the calculation of cross sections in high energy collisions at NLO, one option is to perform all of the integrations, including the virtual loop integration, by Monte Carlo numerical integration. A new method is developed to perform the loop integration directly, without introducing Feynman parameters, after suitably deforming the integration contour. Our example is the N-photon scattering amplitude with a massless electron loop. Results for six photons and eight photons are reported.
Committee in charge: Stephen Hsu, Chairperson, Physics; Graham Kribs, Member, Physics; David Strom, Member, Physics; Davison Soper, Member, Physics; Marina Guenza, Outside Member, Chemistry
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Jiao, Yalong. "Computational discovery and electronic engineering in nanomaterials for photovoltaic and electronic applications." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/116196/1/Yalong_Jiao_Thesis.pdf.
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This thesis is a computational study for the discovery of nanomaterials for energy and electronic applications. It successfully predicted a series of structures with excellent optical and novel electronic properties. The comprehensive work is expected to guide the experimental realization of next-generation photoelectric and electronic devices in the near future.
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Ullah, Habib. "First-principles density functional theory study of novel materials for solar energy conversion and environment applications." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32949.
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To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.
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GOGI, VAMSHI KIRAN. "New Insights into Topological Phases in (Na2O)x(P2O5)100-x glasses from Enthalpy of Relaxation at Tg from Modulated-DSC and LO- and TO- mode frequency splitting from IR reflectance." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1593268824449037.
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Maakestad, Helge. "Principal Parts on P^1 and Chow-groups of the classical discriminants." Doctoral thesis, KTH, Mathematics, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3022.
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Lestang, Thibault. "Numerical simulation and rare events algorithms for the study of extreme fluctuations of the drag force acting on an obstacle immersed in a turbulent flow." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN049/document.
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Cette thèse porte sur l'étude numérique des fluctuations extrêmes de la force de traînée exercée par un écoulement turbulent sur un corps immergé.Ce type d'évènement, très rare, est difficile à caractériser par le biais d'un échantillonnage direct, puisqu'il est alors nécessaire de simuler l'écoulement sur des durées extrêmement longues. Cette thèse propose une approche différente, basée sur l'application d'algorithmes d'échantillonnage d'événements rares. L'objectif de ces algorithmes, issus de la physique statistique, est de modifier la statistique d'échantillonnage des trajectoires d'un système dynamique, de manière à favoriser l'occurrence d'événements rares. Si ces techniques ont été appliquées avec succès dans le cas de dynamiques relativement simples, l'intérêt de ces algorithmes n'est à ce jour pas clair pour des dynamiques déterministes extrêmement complexes, comme c'est le cas pour les écoulement turbulents.Cette thèse présente tout d'abord une étude de la dynamique et de la statistique associée aux fluctuations extrêmes de la force de traînée sur un obstacle carré fixe immergé dans un écoulement turbulent à deux dimensions. Ce cadre simplifié permet de simuler la dynamique sur des durées très longues, permettant d'échantillonner un grand nombre de fluctuations dont l'amplitude est assez élevée pour être qualifiée d'extrême.Dans un second temps, l'application de deux algorithmes d’échantillonnage est présentée et discutée.Dans un premier cas, il est illustré qu'une réduction significative du temps de calcul d'extrêmes peut être obtenue. En outre, des difficultés liées à la dynamique de l'écoulement sont mises en lumière, ouvrant la voie au développement de nouveaux algorithmes spécifiques aux écoulements turbulentsThis thesis discusses the numerical simulation of extreme fluctuations of the drag force acting on an object immersed in a turbulent medium.Because such fluctuations are rare events, they are particularly difficult to investigate by means of direct sampling. Indeed, such approach requires to simulate the dynamics over extremely long durations.In this work an alternative route is introduced, based on rare events algorithms.The underlying idea of such algorithms is to modify the sampling statistics so as to favour rare trajectories of the dynamical system of interest.These techniques recently led to impressive results for relatively simple dynamics. However, it is not clear yet if such algorithms are useful for complex deterministic dynamics, such as turbulent flows.This thesis focuses on the study of both the dynamics and statistics of extreme fluctuations of the drag experienced by a square cylinder mounted in a two-dimensional channel flow.This simple framework allows for very long simulations of the dynamics, thus leading to the sampling of a large number of events with an amplitude large enough so as they can be considered extreme.Subsequently, the application of two different rare events algorithms is presented and discussed.In the first case, a drastic reduction of the computational cost required to sample configurations resulting in extreme fluctuations is achieved.Furthermore, several difficulties related to the flow dynamics are highlighted, paving the way to novel approaches specifically designed to turbulent flows
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Rogozhin, Alexander. "Approximation Methods for Two Classes of Singular Integral Equations." Doctoral thesis, Universitätsbibliothek Chemnitz, 2003. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200300091.
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The dissertation consists of two parts. In the first part approximate methods for multidimensional weakly singular integral operators with operator-valued kernels are investigated. Convergence results and error estimates are given. There is considered an application of these methods to solving radiation transfer problems. Numerical results are presented, too. In the second part we consider a polynomial collocation method for the numerical solution of a singular integral equation over the interval. More precisely, the operator of our integral equation is supposed to be of the form \ $aI + b \mu^{-1} S \mu I $\ with \ $S$\ the Cauchy singular integral operator, with piecewise continuous coefficients \ $a$\ and \ $b,$\ and with a Jacobi weight \ $\mu.$\ To the equation we apply a collocation method, where the collocation points are the Chebyshev nodes of the first kind and where the trial space is the space of polynomials multiplied by another Jacobi weight. For the stability and convergence of this collocation method in weighted \ $L^2$\ spaces, we derive necessary and sufficient conditions. Moreover, the extension of these results to an algebra generated by the sequences of the collocation method applied to the mentioned singular integral operators is discussed and the behaviour of the singular values of the discretized operators is investigatedDie Dissertation beschäftigt sich insgesamt mit der numerischen Analysis singulärer Integralgleichungen, besteht aber aus zwei voneinander unabhängigen Teilen. Der este Teil behandelt Diskretisierungsverfahren für mehrdimensionale schwach singuläre Integralgleichungen mit operatorwertigen Kernen. Darüber hinaus wird hier die Anwendung dieser allgemeinen Resultate auf ein Strahlungstransportproblem diskutiert, und numerische Ergebnisse werden präsentiert. Im zweiten Teil betrachten wir ein Kollokationsverfahren zur numerischen Lösung Cauchyscher singulärer Integralgleichungen auf Intervallen. Der Operator der Integralgleichung hat die Form \ $aI + b \mu^{-1} S \mu I $\ mit dem Cauchyschen singulären Integraloperator \ $S,$\ mit stückweise stetigen Koeffizienten \ $a$\ und \ $b,$\ und mit einem klassischen Jacobigewicht \ $\mu.$\ Als Kollokationspunkte dienen die Nullstellen des n-ten Tschebyscheff-Polynoms erster Art und Ansatzfunktionen sind ein in einem geeigneten Hilbertraum orthonormales System gewichteter Tschebyscheff-Polynome zweiter Art. Wir erhalten notwendige und hinreichende Bedingungen für die Stabilität und Konvergenz dieses Kollokationsverfahrens. Außerdem wird das Stabilitätskriterium auf alle Folgen aus der durch die Folgen des Kollokationsverfahrens erzeugten Algebra erweitert. Diese Resultate liefern uns Aussagen über das asymptotische Verhalten der Singulärwerte der Folge der diskreten Operatoren
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Bauerheim, Michaël. "Étude théorique et numérique des effets de brisures de symétrie sur les modes thermo-acoustiques azimutaux dans les chambres annulaires." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0107/document.
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Une large gamme de problèmes physiques, des petites molécules aux étoiles géantes, contiennent des symétries de rotation et sont sujets à des oscillations azimutales ou transverses. Quand cette symétrie est rompue, le système peut devenir instable. Dans cette thèse, les brisures de symétries sont étudiées dans les chambres de combustion annulaires, sujettes à des instabilités thermo-acoustiques azimutales. En premier lieu, deux types de brisures sont obtenus analytiquement : la première en répartissant des bruleurs différents le long de la chambre et la seconde provoquée par le champ moyen lui-même. Ces ruptures de symétries entraînent une séparation des fréquences, fixe la structure du mode et peut déstabiliser le système. De plus, une approche Quantification d’Incertitudes (UQ) permet d’évaluer l’effet de la rupture de symétries provoquée par les incertitudes sur la description ou le comportement des flammes. Pour compléter cette théorie, des Simulations aux Grandes Echelles (SGE) sont réalisées sur un mono-secteur ainsi que sur une configuration complète 360° de l’expérience annulaire de Cambridge. Les résultats numériques sont comparés aux données expérimentales et montrent un bon accord. En particulier, un mode instable à 1800 Hz croît dans les deux cas. Cependant, la SGE, limitée par son coût important, ne permet pas l’étude du cycle limite s’établissant après plusieurs centaines de millisecondes. Pour pallier à ce problème, une nouvelle approche, appelée AMT, est développée : les résultats d’une théorie ou d’un solveur acoustique sont injectés dans une simulation SGE. Cette approche permet d’étudier les brisures de symétries, la nature et la dynamique des modes acoustiques, ainsi que d’évaluer l’amortissement dans des configurations réalistesA large range of physical problems, from molecules to giant stars, contains rotating symmetry and can exhibit azimuthal waves or vibrations. When this symmetry is broken, the system can become unstable with chaotic behaviors. Symmetry breaking is investigated in annular combustors prone to azimuthal thermo-acoustic instabilities. First, theories reveal that two types of symmetry breaking exist : due to different burner types distributed along the chamber or due to the flow itself . It leads to frequency splitting, fixes the mode structure and can destabilize the configuration. A UQ analysis is also performed to quantify the symmetry breaking effect due to uncertainties of flame descriptions or behaviors. To complete theory, Large Eddy Simulations are performed on a single-sector as well as on a complete 360° configuration of the annular experiment of Cambridge. Numerical results are compared to experimental data showing a good agreement. In particular, an unstable azimuthal mode at 1800 Hz grows in both LES and experiment. However, LES cannot investigate the limit cycle because of its extreme cost. To tackle this problem, a new methodology is developed, called AMT, where theory or Helmholtz solver predictions are injected into LES or DNS. This method allows to study symmetry breaking, mode nature and dynamics as well as evaluating damping in realistic annular configurations
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Matta, Sri Kasi Venkata Nageswara Rao. "Computational exploration of two-dimensional (2D) materials for solar energy applications." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/134244/1/Sri%20Kasi%20Venkata%20Nageswara%20Rao%20Matta%20Thesis_Redacted.pdf.
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This project is to find innovative and alternate Nano-sized materials for solar energy applications. This include conversion of solar light energy into electricity or generate clean environment friendly fuels by breaking water into Oxygen and Hydrogen. The study has explored material characteristics at electronic level to reveal new properties. These revelations then compared amongst some of the organic and inorganic materials for the intended purpose. Innovative design of new carbon-compounds (termed as carbon Quantum dots) included in the study for use in the new generation Perovskite solar cells for charge transfer.
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Garat, Philippe. "Approche statistique pour la séparation aveugle de sources." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10227.
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Nous considerons dans cette these le probleme de la separation aveugle de signaux aleatoires independants, dans le cadre des melanges lineaires instantanes inversibles non bruites. Par une approche de maximum de vraisemblance, nous traitons deux situations distinctes: tout d'abord le cas des signaux temporellement independants et non gaussiens, puis le cas des signaux temporellement correles stationnaires au second ordre avec spectres distincts. Dans chacun des deux cas, nous proposons un systeme approprie d'equations de separation. La premiere methode de separation est fondee sur des fonctions separatrices non lineaires et s'apparente a ce titre a la methode connue herault-jutten. Nous indiquons une resolution iterative de type newton, qui necessite une bonne initialisation pour eviter la convergence sur une solution parasite. La deuxieme methode constitue une analyse statistique au second ordre, et s'exprime a l'aide de filtres separateurs lineaires. Outre une resolution generale iterative, il existe dans certains situations une resolution directe (double-diagonalisation de deux matrices symetriques). Une analyse theorique des performances asymptotiques des deux methodes est presentee. Cela permet en particulier de mettre en evidence les choix optimaux des fonctions et filtre separateurs. Dans tous les cas, les performances asymptotiques ne dependent pas des parametres du melange, mais seulement des statistiques des sources et des fonctions/filtres separateurs. Pour terminer, nous presentons quelques resultats de simulations numeriques qui montrent une bonne concordance avec la theorie. Une illustration sur signaux reels est egalement donnee
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Straßburger, Lutz. "Linear Logic and Noncommutativity in the Calculus of Structures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2003. http://nbn-resolving.de/urn:nbn:de:swb:14-1063208959250-72937.
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In this thesis I study several deductive systems for linear logic, its fragments, and some noncommutative extensions. All systems will be designed within the calculus of structures, which is a proof theoretical formalism for specifying logical systems, in the tradition of Hilbert's formalism, natural deduction, and the sequent calculus. Systems in the calculus of structures are based on two simple principles: deep inference and top-down symmetry. Together they have remarkable consequences for the properties of the logical systems. For example, for linear logic it is possible to design a deductive system, in which all rules are local. In particular, the contraction rule is reduced to an atomic version, and there is no global promotion rule. I will also show an extension of multiplicative exponential linear logic by a noncommutative, self-dual connective which is not representable in the sequent calculus. All systems enjoy the cut elimination property. Moreover, this can be proved independently from the sequent calculus via techniques that are based on the new top-down symmetry. Furthermore, for all systems, I will present several decomposition theorems which constitute a new type of normal form for derivations.
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Rogozhin, Alexander. "Approximation methods for two classes of singular integral equations." Doctoral thesis, [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=968783279.
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Otten, Brooke Michelle. "Computational and Experimental Studies of the Photoluminescence, Reactivity and Structural Properties of d10 and d8 Metal Complexes." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1505232/.
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Computational chemistry has gained interest as a characterization tool to predict photoluminescence, reactivity and structural properties of organic and transition metal complexes. With the rise of methods including relativity, these studies have been expanded to the accurate modeling of luminescence spectra of complexes with considerable spin-orbit splitting due to heavy metal centers as well as the reaction pathways for these complexes to produce natural products such as hydrogen gas. These advances have led to the synthesis and utility of more effective catalysis as well as the development of more effective organic light emitting diodes (OLEDs) through the incorporation of organometallic complexes as emitters instead of typical organic emitters. In terms of significant scientific advancement presented in this work is in relation to the discovery of significant spin-orbit splitting in a gold(I) alkylphosphine complex, where the splitting results in the states that emit in different colors of the visible region of the electromagnetic spectrum. This work also reveals the discovery both computationally and experimentally, of a genuine polar-covalent bond between two-closed shell metals. This work highlights a complex with an incredibly short gold(I) – copper(I) intermetallic distance leading to a vibrational frequency and dissociation energy that is on par with those of other systems with single-bonded metal centers. Lastly, this work outlines a strategy for the production of hydrogen gas through the use of trinuclear cyclic coinage metal complexes as catalysis to split hydrohalic acids.
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Santos, Filipe Daniel Rodrigues. "Critical magnetic elds in superconducting systems with semi-metallic bands." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/16074.
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Mestrado em FísicaIn this work, we study the Zeeman splitting effects in the parallel magnetic field versus temperature phase diagram of two-dimensional superconductors with one graphene-like band and the orbital effects of perpendicular magnetic fields in isotropic two-dimensional semi-metallic superconductors. We show that when parallel magnetic fields are applied to graphene and as the intraband interaction decreases to a critical value, the width of the metastability region present in the phase diagram decreases, vanishing completely at that critical value. In the case of two-band superconductors with one graphene-like band, a new critical interaction, associated primarily with the graphene-like band, is required in order for a second metastability region to be present in the phase diagram. For intermediate values of this interaction, a low-temperature first-order transition line bifurcates at an intermediate temperature into a first-order transition between superconducting phases and a second-order transition line between the normal and the superconducting states. In our study on the upper critical fields in generic semi-metallic superconductors, we find that the pair propagator decays faster than that of a superconductor with a metallic band. As result, the zero field band gap equation does not have solution for weak intraband interactions, meaning that there is a critical intraband interaction value in order for a superconducting phase to be present in semi-metallic superconductors. Finally, we show that the out-of-plane critical magnetic field versus temperature phase diagram displays a positive curvature, contrasting with the parabolic-like behaviour typical of metallic superconductors.
Neste trabalho, estudamos o efeito de Zeeman nos diagramas de fases do campo magnético versus temperatura de supercondutores bidimensionais com uma banda de grafeno na sua composição, sobre a ação de campos magnéticos paralelos e os efeitos orbitais em supercondutores semimetálicos bidimensionais e isotrópicos sobre a ação de campos magnéticos perpendiculares. Mostramos que quando se aplica campos magnéticos paralelamente a uma camada de grafeno e à medida que a interação da banda diminui, a largura da zona de metastabilidade presente no diagrama de fases diminui, desaparecendo por completo quando a interação toma um valor crítico. No caso de supercondutors de duas bandas com uma banda de grafeno, existe uma nova interação crítica, associada principalmente à banda de grafeno, necessária ao surgimento de uma segunda zona de metastabilidade no diagrama de fases. Para valores intermédios dessa interação, a transição de primeira ordem que surge, no diagrama de fases, a baixas temperaturas, ramifica-se, a temperaturas intermedias, numa transição de primeira ordem entre fases supercondutoras e numa transição de segunda ordem entre os estados não supercondutor e supercondutor. Em relação ao nosso estudo, sobre os efeitos orbitais em supercondutores semimetálicos genéricos, descobrimos que o propagador de pares decai, com a distância, mais depressa do que no caso de um supercondutor metálico. Como consequência, a equação de gap a campo nulo não tem solução para fracas interações da banda semimetálica indicando a existência de um valor crítico para a interação da banda necessária à existência de uma fase supercondutora em supercondutores semimetálicos. Mostramos finalmente que o diagrama de fases do campo crítico magnético versus temperatura exibe uma curvatura positiva em contraste com a curva parabólica do diagrama de fases típico de supercondutores metálicos.
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Chen, Bo. "Partly exchangeable fragmentations." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:0e841fd3-51fa-4c72-be9f-08477e74d703.
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We introduce a simple tree growth process that gives rise to a new two-parameter family of discrete fragmentation trees that extends Ford's alpha model to multifurcating trees and includes the trees obtained by uniform sampling from Duquesne and Le Gall's stable continuum random tree. We call these new trees the alpha-gamma trees. In this thesis, we obtain their splitting rules, dislocation measures both in ranked order and in sized-biased order, and we study their limiting behaviour. We further extend the underlying exchangeable fragmentation processes of such trees into partly exchangeable fragmentation processes by weakening the exchangeability. We obtain the integral representations for the measures associated with partly exchangeable fragmentation processes and subordinator of the tagged fragments. We also embed the trees associated with such processes into continuum random trees and study their limiting behaviour. In the end, we generate a three-parameter family of partly exchangeable trees which contains the family of the alpha-gamma trees and another important two-parameter family based on Poisson-Dirichlet distributions.
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Henter, Gustav Eje. "Probabilistic Sequence Models with Speech and Language Applications." Doctoral thesis, KTH, Kommunikationsteori, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-134693.
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Series data, sequences of measured values, are ubiquitous. Whenever observations are made along a path in space or time, a data sequence results. To comprehend nature and shape it to our will, or to make informed decisions based on what we know, we need methods to make sense of such data. Of particular interest are probabilistic descriptions, which enable us to represent uncertainty and random variation inherent to the world around us. This thesis presents and expands upon some tools for creating probabilistic models of sequences, with an eye towards applications involving speech and language. Modelling speech and language is not only of use for creating listening, reading, talking, and writing machines---for instance allowing human-friendly interfaces to future computational intelligences and smart devices of today---but probabilistic models may also ultimately tell us something about ourselves and the world we occupy. The central theme of the thesis is the creation of new or improved models more appropriate for our intended applications, by weakening limiting and questionable assumptions made by standard modelling techniques. One contribution of this thesis examines causal-state splitting reconstruction (CSSR), an algorithm for learning discrete-valued sequence models whose states are minimal sufficient statistics for prediction. Unlike many traditional techniques, CSSR does not require the number of process states to be specified a priori, but builds a pattern vocabulary from data alone, making it applicable for language acquisition and the identification of stochastic grammars. A paper in the thesis shows that CSSR handles noise and errors expected in natural data poorly, but that the learner can be extended in a simple manner to yield more robust and stable results also in the presence of corruptions. Even when the complexities of language are put aside, challenges remain. The seemingly simple task of accurately describing human speech signals, so that natural synthetic speech can be generated, has proved difficult, as humans are highly attuned to what speech should sound like. Two papers in the thesis therefore study nonparametric techniques suitable for improved acoustic modelling of speech for synthesis applications. Each of the two papers targets a known-incorrect assumption of established methods, based on the hypothesis that nonparametric techniques can better represent and recreate essential characteristics of natural speech. In the first paper of the pair, Gaussian process dynamical models (GPDMs), nonlinear, continuous state-space dynamical models based on Gaussian processes, are shown to better replicate voiced speech, without traditional dynamical features or assumptions that cepstral parameters follow linear autoregressive processes. Additional dimensions of the state-space are able to represent other salient signal aspects such as prosodic variation. The second paper, meanwhile, introduces KDE-HMMs, asymptotically-consistent Markov models for continuous-valued data based on kernel density estimation, that additionally have been extended with a fixed-cardinality discrete hidden state. This construction is shown to provide improved probabilistic descriptions of nonlinear time series, compared to reference models from different paradigms. The hidden state can be used to control process output, making KDE-HMMs compelling as a probabilistic alternative to hybrid speech-synthesis approaches. A final paper of the thesis discusses how models can be improved even when one is restricted to a fundamentally imperfect model class. Minimum entropy rate simplification (MERS), an information-theoretic scheme for postprocessing models for generative applications involving both speech and text, is introduced. MERS reduces the entropy rate of a model while remaining as close as possible to the starting model. This is shown to produce simplified models that concentrate on the most common and characteristic behaviours, and provides a continuum of simplifications between the original model and zero-entropy, completely predictable output. As the tails of fitted distributions may be inflated by noise or empirical variability that a model has failed to capture, MERS's ability to concentrate on high-probability output is also demonstrated to be useful for denoising models trained on disturbed data.QC 20131128
ACORNS: Acquisition of Communication and Recognition Skills
LISTA – The Listening Talker
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Júnior, Antônio Espósito. "Equações integrais via teoria de domínios: problemas direto e inverso." Universidade do Estado do Rio de Janeiro, 2008. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=772.
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Apresenta-se um estudo em Teoria de Domínios das equações integrais da forma geral
f (x) = h(x)+g Z b(x)
a(x)
g(x, y, f (y))dy
com h, a e b definidas para x ∈ [a0,b0], a0 ≤a(x)≤b(x)≤b0 e g definida para x, y ∈ [a0,b0], cujo lado direito define uma contração sobre o espaço métrico de funções reais contínuas
limitadas. O ponto de partida desse trabalho é a reescrita da Análise Intervalar para Teoria de Domínios do problema de valor incial em equações diferenciais ordinárias que possuem
solução como ponto fixo do operador de Picard. Com o conjunto dos números reais interpretados pelo Domínio Intervalar, as funções reais são estendidas para operarem no domínio de funçoes intervalares de variável real. Em particular, faz-se a extensão canônica do campo vetorial em relação à segunda variável. Nesse contexto, pela primeira vez tem-se o estudo das equações integrais de Fredholm e Volterra sobre o domínio de funções intervalares de variável real definida pelo operador integral intervalar com a participação da extensão canônica de g em relação à terceira variável. Adicionando ao domínio de funções intervalares sua função medição, efetua-se a análise da convergência do operador intervalar de Fredholm e Volterra em Teoria de Domínios com o cálculo da sua derivada
informática em relação à medição no seu ponto fixo. Com a representação das funções intervalares em função passo constante a partir da partição do intervalo [a0,b0], reescrevese
o algoritmo da Análise Intervalar em Teoria de Domínios com a introdução do cálculo da aproximação da extensão canônica de g e com o comprimento do intervalo da partição tendendo para zero. Estende-se essa abordagem mais completa do estudo das equações integrais na resolução de problemas de valores iniciais e valor de contorno em equações diferenciais ordinárias e parciais. Uma vez que para uma pequena variação do campo
vetorial v ou do valor inicial y0 da equação diferencial f ′(x) = v(x, f (x)) com a condição inicial f (x0) = y0, pode-se ter uma solução tão próxima da solução f da equação quanto
possível, formaliza-se pela primeira vez em Teoria de Domínios um algoritmo na resolução do problema inverso em que, conhecendo a função f , determina-se uma equação diferencial
ordinária com o cálculo de um campo vetorial v tal que o operador de Picard associado mapeia f tão próxima quanto possível a ela mesma.We present a study in Domain Theory of integral equations of the form f (x) = h(x)+g Z b(x) a(x) g(x, y, f (y))dy for a0 ≤ a(x) ≤ b(x) ≤ b0 with h, a, b defined for x ∈ [a0,b0] and g defined for x, y ∈ [a0,b0], in which the right-hand side defines a contraction on the metric space of continuous realvalued functions on [a0,b0]. The starting point of this work is to revisit Interval Analysis in Domain Theory for the initial-value problem in ordinary differential equations where a solution is expressed as a fixed point of the Picard operator. With the set of real numbers interpreted as the interval domain, real-valued functions are extended to work in the space of interval-valued functions of the real variable domain. In particular, the vector field is extended in the second argument. Under these conditions, for the first time Fredholm and Volterra integral equations have solutions expressed as fixed points of a contraction mapping in terms of the splitting on interval-valued functions of the real variable domain. The measurement for interval-valued functions of the real variable domain is considered where we can asssess the convergence properties of the interval integral operator by means of the informatic derivative. The proposed techniques are applied to more general methods in ordinary differencial equations (ODEs) and partial differential equations (PDEs). For the first time, an algorithm is proposed to provide solutions to the inverse problem for Odinary Differential Equation where, given a function f , it is found a vector field v that defines a Picard operator which maps the solution f as close as possible to itself, such that the ODE f ′(x) = v(x, f (x)) admits f as either an exact or, as closely as desired, an approximate solution.
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Bain, Katherine Alison. "Chased by the dragon the experience of relapse in cocaine and heroin users /." Diss., Pretoria : [s.n.], 2004. http://upetd.up.ac.za/thesis/available/etd-10192004-100341.
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Wörner, Andreas [Verfasser]. "Boundary strata of nonnegatively curved Alexandrov Spaces and a splitting theorem / vorgelegt von Andreas Wörner." 2010. http://d-nb.info/1007714565/34.
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Park, Daeshik. "The Fekete-Szegö theorem with splitting conditions on the projective line of positive characteristic p." 2006. http://purl.galileo.usg.edu/uga%5Fetd/park%5Fdaeshik%5F200608%5Fphd.
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Dung, Nguyen Thac, and 阮碩勇. "Some Splitting and Vanishing Type Theorems on Complete Manifolds." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/16994057580596347056.
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Kuo, Yen-Ting, and 郭彥廷. "Limit Theorems for the Cost of Splitting Random Cayley Trees." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/24068832006181372227.
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碩士國立交通大學
應用數學系所
100
In computer science, the so-called "Union-Find problem" is concerned with establishing a data structure for maintaining a collection of disjoint sets such that the process of merging sets can be carried out efficiently. Indeed, several data structures and corresponding algorithms for merging sets have been proposed. For the purpose of comparing the complexity of these algorithms, it is naturally to consider the total cost incurred from merging n singleton sets into one set. In this thesis, we assume that the cost of each merging step is the power of the sum of the sizes of the sets being merged and then derive the expected value and the limiting distribution of the total cost under the random spanning tree model. The main tool used in this thesis is singularity analysis, which is a method connecting the asymptotics of generating functions with the asymptotics of their coefficients. We will use it to derive the moments of each order. Then, with the method of moments, the limiting distribution of the total cost will follow. In the first part of this thesis (Chapter 1), we introduce the problem of interest and state the results of our work. In Chapter 2, we give an introduction about our main tool, singularity analysis. The central part of this thesis, namely Chapter 3, is devoted to the derivation of the expected value and higher moments. These results will will then be used in Chapter 4 for prove our main result. Finally, we end the thesis with a conclusion in Chapter 5.
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Seidel, Markus. "Über die Splitting-Eigenschaft der Approximationszahlen von Matrix-Folgen: l1-Theorie." Master's thesis, 2006. https://monarch.qucosa.de/id/qucosa%3A18658.
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In dieser Arbeit wird das asymptotische Verhalten der Approximationszahlen für Operatorfolgen aus einer speziellen Klasse von Banachalgebren untersucht. Es werden bemerkenswerte Eigenschaften der Folgen und der Approximationszahlen ihrer Operatoren gezeigt, darunter die so genannte splitting-Eigenschaft.
Ein typisches Beispiel solcher Operatorfolgen stellen die Finite Sections von Toeplitzoperatoren dar, die exemplarisch behandelt werden. Dabei werden hier auch die Folgenräume l1 und l-unendlich betrachtet.
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Tseng, Guo-En, and 曾國恩. "Stable splitting of the complex connective K-theory of BSO(8)." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/9twj8n.
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Wu, Tsung-Hsuan, and 吳宗軒. "Stable splitting of the complex connective K-theory of BSO(2n+1)." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/8xd4b5.
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博士國立清華大學
數學系所
106
Through the algebraic splitting of the cohomology over the exterior algebra E=ℤ/2