Dissertations / Theses: 'Metric geometry of singularities'

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Oudrane, M'hammed. "Projections régulières, structure de Lipschitz des ensembles définissables et faisceaux de Sobolev." Electronic Thesis or Diss., Université Côte d'Azur, 2023. http://www.theses.fr/2023COAZ4034.

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Dans cette thèse, nous abordons des questions autour de la structure métrique des ensembles définissables dans les structures o-minimales.Dans la première partie, nous étudions les projections régulières au sens de Mostowski, nous prouvons que ces projections n'existent que pour les structures polynomialement bornées, nous utilisons les projections régulières pour refaire la preuve de Parusinski de l'existence des recouvrements réguliers. Dans la deuxième partie de cette thèse, nous étudions les faisceaux de Sobolev (au sens de Lebeau). Pour les fonctions de Sobolev de régularité entière positive, nous construisons ces faisceaux sur le site définissable d'une surface en nous basant sur des observations de base des domaines définissables dans le plan
In this thesis we address questions around the metric structure of definable sets in o-minimal structures. In the first part we study regular projections in the sense of Mostowski, we prove that these projections exists only for polynomially bounded structures, we use regular projections to re perform Parusinski's proof of the existence of regular covers. In the second part of this thesis, we study Sobolev sheaves (in the sense of Lebeau). For Sobolev functions of positive integer regularity, we construct these sheaves on the definable site of a surface based on basic observations of definable domains in the plane

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Lebl, Jiří́. "Singularities and Complexity in CR Geometry." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3254327.

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Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed May 2, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 101-104).

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Ronaldson, Luke James. "The geometry of weak gravitational singularities." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485292.

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Coffey, Michael R. "Ricci flow and metric geometry." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/67924/.

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This thesis considers two separate problems in the field of Ricci flow on surfaces. Firstly, we examine the situation of the Ricci flow on Alexandrov surfaces, which are a class of metric spaces equipped with a notion of curvature. We extend the existence and uniqueness results of Thomas Richard in the closed case to the setting of non-compact Alexandrov surfaces that are uniformly non-collapsed. We complement these results with an extensive survey that collects together, for the first time, the essential topics in the metric geometry of Alexandrov spaces due to a variety of authors. Secondly, we consider a problem in the well-posedness theory of the Ricci flow on surfaces. We show that given an appropriate initial Riemannian surface, we may construct a smooth, complete, immortal Ricci flow that takes on the initial surface in a geometric sense, in contrast to the traditional analytic notions of initial condition. In this way, we challenge the contemporary understanding of well-posedness for geometric equations.

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van, Staden Wernd Jakobus. "Metric aspects of noncommutative geometry." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/77893.

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We study noncommutative geometry from a metric point of view by constructing examples of spectral triples and explicitly calculating Connes's spectral distance between certain associated pure states. After considering instructive nite-dimensional spectral triples, the noncommutative geometry of the in nite-dimensional Moyal plane is studied. The corresponding spectral triple is based on the Moyal deformation of the algebra of Schwartz functions on the Euclidean plane.
Dissertation (MSc)--University of Pretoria, 2019.
Physics
MSc
Unrestricted

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Mangalath, Vishnu. "Singularities of Whitham Deformations." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25990.

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Constant mean curvature planes of finite type in Euclidean 3-space are in correspondence with spectral data, consisting of a hyperelliptic (spectral) curve, two meromorphic differentials, and a line bundle. A class of deformations one can consider are known as Whitham or period preserving deformations. Singularities of Whitham deformations can occur if the differentials have common roots on the spectral curve. In this thesis we are concerned with studying deformations within, and out of, the space of spectral data at which the Whitham equations are singular. We show in a special case that singular Whitham deformations correspond to certain planar graphs on CP1, and study the existence theory of these graphs.

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Palmer, Ian Christian. "Riemannian geometry of compact metric spaces." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34744.

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A construction is given for which the Hausdorﬀ measure and dimension of an arbitrary abstract compact metric space (X, d) can be encoded in a spectral triple. By introducing the concept of resolving sequence of open covers, conditions are given under which the topology, metric, and Hausdorﬀ measure can be recovered from a spectral triple dependent on such a sequence. The construction holds for arbitrary compact metric spaces, generalizing previous results for fractals, as well as the original setting of manifolds, and also holds when Hausdorﬀ and box dimensions diﬀer---in particular, it does not depend on any self-similarity or regularity conditions on the space. The only restriction on the space is that it have positive s₀ dimensional Hausdorﬀ measure, where s₀ is the Hausdorﬀ dimension of the space, assumed to be ﬁnite. Also, X does not need to be embedded in another space, such as Rⁿ.

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Jägrell, Linus. "Geometry of the Lunin-Maldacena metric." Thesis, KTH, Teoretisk fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-153502.

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Milicevic, Luka. "Topics in metric geometry, combinatorial geometry, extremal combinatorics and additive combinatorics." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273375.

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Persson, Nicklas. "Shortest paths and geodesics in metric spaces." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-66732.

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This thesis is divided into three part, the first part concerns metric spaces and specically length spaces where the existence of shortest path between points is the main focus. In the second part, an example of a length space, the Riemannian geometry will be given. Here both a classical approach to Riemannian geometry will be given together with specic results when considered as a metric space. In the third part, the Finsler geometry will be examined both with a classical approach and trying to deal with it as a metric space.

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Suleymanova, Asilya. "On the spectral geometry of manifolds with conic singularities." Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/18420.

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Wir beginnen mit der Herleitung der asymptotischen Entwicklung der Spur des Wärmeleitungskernes, $\tr e^{-t\Delta}$, für $t\to0+$, wobei $\Delta$ der Laplace-Beltrami-Operator auf einer Mannigfaltigkeit mit Kegel-Singularitäten ist; dabei folgen wir der Arbeit von Brüning und Seeley. Dann untersuchen wir, wie die Koeffizienten der Entwicklung mit der Geometrie der Mannigfaltigkeit zusammenhängen, insbesondere fragen wir, ob die (mögliche) Singularität der Mannigfaltigkeit aus den Koeffizienten - und damit aus dem Spektrum des Laplace-Beltrami-Operators - abgelesen werden kann. In wurde gezeigt, dass im zweidimensionalen Fall ein logarithmischer Term und ein nicht lokaler Term im konstanten Glied genau dann verschwinden, wenn die Kegelbasis ein Kreis der Länge $2\pi$ ist, die Mannigfaltigkeit also geschlossen ist. Dann untersuchen wir wir höhere Dimensionen. Im vier-dimensionalen Fall zeigen wir, dass der logarithmische Term genau dann verschwindet, wenn die Kegelbasis eine sphärische Raumform ist. Wir vermuten, dass das Verschwinden eines nicht lokalen Beitrags zum konstanten Term äquivalent ist dazu, dass die Kegelbasis die runde Sphäre ist; das kann aber bisher nur im zyklischen Fall gezeigt werden. Für geraddimensionale Mannigfaltigkeiten höherer Dimension und mit Kegelbasis von konstanter Krümmung zeigen wir weiter, dass der logarithmische Term ein Polynom in der Krümmung ist, das Wurzeln ungleich 1 haben kann, so dass erst das Verschwinden von mehreren Termen - die derzeit noch nicht explizit behandelt werden können - die Geschlossenheit der Mannigfaltigkeit zur Folge haben könnte.
We derive a detailed asymptotic expansion of the heat trace for the Laplace-Beltrami operator on functions on manifolds with one conic singularity, using the Singular Asymptotics Lemma of Jochen Bruening and Robert T. Seeley. Then we investigate how the terms in the expansion reflect the geometry of the manifold. Since the general expansion contains a logarithmic term, its vanishing is a necessary condition for smoothness of the manifold. It is shown in the paper by Bruening and Seeley that in the two-dimensional case this implies that the constant term of the expansion contains a non-local term that determines the length of the (circular) cross section and vanishes precisely if this length equals $2\pi$, that is, in the smooth case. We proceed to the study of higher dimensions. In the four-dimensional case, the logarithmic term in the expansion vanishes precisely when the cross section is a spherical space form, and we expect that the vanishing of a further singular term will imply again smoothness, but this is not yet clear beyond the case of cyclic space forms. In higher dimensions the situation is naturally more difficult. We illustrate this in the case of cross sections with constant curvature. Then the logarithmic term becomes a polynomial in the curvature with roots that are different from 1, which necessitates more vanishing of other terms, not isolated so far.

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Li, Xining. "Preservation of bounded geometry under transformations metric spaces." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439309722.

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PALMISANO, Vincenzo. "Topics in calculus and geometry on metric spaces." Doctoral thesis, Università degli Studi di Palermo, 2022. https://hdl.handle.net/10447/554772.

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In this thesis we present an overview of some important known facts related to topology, geometry and calculus on metric spaces. We discuss the well known problem of the existence of a lipschitz equivalent metric to a given quasiultrametric, revisiting known results and counterexamples and providing some new theorems, in an unified approach. Also, in the general setting of a quasi-metric doubling space, suitable partition of unity lemmas allows us to obtain, in step two Carnot groups, the well known Whitney’s extension theorem for a given real function of class C^m defined on a closed subset of the whole space: this result relies on relevant properties of the symmetrized Taylor’s polynomial recently introduced in this setting. Finally, some first interesting investigations on Menger convexity in the setting of a general metric spaces concludes this work.

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Lübbe, Christian. "An extension theorem for conformal gauge singularities." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670177.

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Witt, Frederik. "Special metric structures and closed forms." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:30b7a34b-cc46-4981-aee5-964787c1235e.

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In recent work, N. Hitchin described special geometries in terms of a variational problem for closed generic $p$-forms. In particular, he introduced on 8-manifolds the notion of an integrable $PSU(3)$-structure which is defined by a closed and co-closed 3-form. In this thesis, we first investigate this $PSU(3)$-geometry further. We give necessary conditions for the existence of a topological $PSU(3)$-structure (that is, a reduction of the structure group to $PSU(3)$ acting through its adjoint representation). We derive various obstructions for the existence of a topological reduction to $PSU(3)$. For compact manifolds, we also find sufficient conditions if the $PSU(3)$-structure lifts to an $SU(3)$-structure. We find non-trivial, (compact) examples of integrable $PSU(3)$-structures. Moreover, we give a Riemannian characterisation of topological $PSU(3)$-structures through an invariant spinor valued 1-form and show that the $PSU(3)$-structure is integrable if and only if the spinor valued 1-form is harmonic with respect to the twisted Dirac operator. Secondly, we define new generalisations of integrable $G_2$- and $Spin(7)$-manifolds which can be transformed by the action of both diffeomorphisms and 2-forms. These are defined by special closed even or odd forms. Contraction on the vector bundle $Toplus T^*$ defines an inner product of signature $(n,n)$, and even or odd forms can then be naturally interpreted as spinors for a spin structure on $Toplus T^*$. As such, the special forms we consider induce reductions from $Spin(7,7)$ or $Spin(8,8)$ to a stabiliser subgroup conjugate to $G_2 times G_2$ or $Spin(7) times Spin(7)$. They also induce a natural Riemannian metric for which we can choose a spin structure. Again we state necessary and sufficient conditions for the existence of such a reduction by means of spinors for a spin structure on $T$. We classify topological $G_2 times G_2$-structures up to vertical homotopy. Forms stabilised by $G_2 times G_2$ are generic and an integrable structure arises as the critical point of a generalised variational principle. We prove that the integrability conditions on forms imply the existence of two linear metric connections whose torsion is skew, closed and adds to 0. In particular we show these integrability conditions to be equivalent to the supersymmetry equations on spinors in supergravity theory of type IIA/B with NS-NS background fields. We explicitly determine the Ricci-tensor and show that over compact manifolds, only trivial solutions exist. Using the variational approach we derive weaker integrability conditions analogous to weak holonomy $G_2$. Examples of generalised $G_2$- and $Spin(7)$ structures are constructed by the device of T-duality.

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Kourliouros, Konstantinos. "Boundary singularities of functions in symplectic and volume-preserving geometry." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/32268.

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In this thesis we study the classi cation problem of boundary singularities of functions in symplectic and volume-preserving geometry. In particular we generalise several well known theorems concerning the classi cation of isolated singularities of functions and volume forms in the presence of a \boundary", i.e. a germ of a xed smooth hypersurface. The results depend in turn on a generalisation of the relative de Rham cohomology and the corresponding Gauss-Manin theory to the case of isolated boundary singularities and in particular, on a relative version of the so called Brieskorn-Deligne-Sebastiani theorem, concerning the niteness and freeness of certain cohomology modules.

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Lopez, Marcos D. "Discrete Approximations of Metric Measure Spaces with Controlled Geometry." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439305529.

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Luo, Ye. "Linear systems on metric graphs and some applications to tropical geometry and non-archimedean geometry." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52323.

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The divisor theories on finite graphs and metric graphs were introduced systematically as analogues to the divisor theory on algebraic curves, and all these theories are deeply connected to each other via tropical geometry and non-archimedean geometry. In particular, rational functions, divisors and linear systems on algebraic curves can be specialized to those on finite graphs and metric graphs. Important results and interesting problems, including a graph-theoretic Riemann-Roch theorem, tropical proofs of conventional Brill-Noether theorem and Gieseker-Petri theorem, limit linear series on metrized complexes, and relations among moduli spaces of algebraic curves, non-archimedean analytic curves, and metric graphs are discovered or under intense investigations. The content in this thesis is divided into three main subjects, all of which are based on my research and are essentially related to the divisor theory of linear systems on metric graphs and its application to tropical geometry and non-archimedean geometry. Chapter 1 gives an overview of the background and a general introduction of the main results. Chapter 2 is on the theory of rank-determining sets, which are subsets of a metric graph that can be used for the computation of the rank function. A general criterion is provided for rank-determining sets and certain specific examples of finite rank-determining sets are presented. Chapter 3 is on the subject of a tropical convexity theory on linear systems on metric graphs. In particular, the notion of general reduced divisors is introduced as the main tool used to study this tropical convexity theory. Chapter 4 is on the subject of smoothing of limit linear series of rank one on re_ned metrized complexes. A general criterion for smoothable limit linear series of rank 1 is presented and the relations between limit linear series of rank 1 and possible harmonic morphisms to genus 0 metrized complexes are studied.

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Alekseevsky, Dmitri, Andreas Kriegl, Mark Losik, Peter W. Michor, and Peter Michor@esi ac at. "The Riemannian Geometry of Orbit Spaces. The Metric, Geodesics, and." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi997.ps.

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Ivrii, Oleg. "The Geometry of the Weil-Petersson Metric in Complex Dynamics." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11669.

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In this work, we study an analogue of the Weil-Petersson metric on the space of Blaschke products of degree 2 proposed by McMullen. We show that the Weil-Petersson metric is incomplete and study its metric completion. Our work parallels known results for the Teichmuller space of a punctured torus.
Mathematics

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Son, Do Nguyen. "McKay quivers and the deformation and resolution theory of kleinen singularities." Bonn : Mathematisches Institut der Universität, 2005. http://catalog.hathitrust.org/api/volumes/oclc/65375195.html.

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Julian, Poranee K. "Geometric Properties of the Ferrand Metric." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353088820.

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Galeotti, Mattia Francesco. "Moduli of curves with principal and spin bundles : singularities and global geometry." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066485/document.

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L'espace de modules Mgbar des courbes stables de genre g est un object central en géométrie algébrique. Du point de vue de la géométrie birationelle, il apparaît naturel se demander si Mgbar est de type générale. Harris-Mumford et Eisenbud-Harris ont montré que Mgbar est de type générale pour un genre g>=24 et g=22. Le cas g=23 est encore misterieux. Dans les dix dernières années une nouvelle approche a émergé, dans l'essai de clarifier ça : l'idée est celle de considérer de recouvrement fini de Mgbar qui sont des espaces de modules de courbes stables munies d'une structure additionnelle comme un l-recouvrement (racine l-ième du fibré trivial) ou un fibré l-spin (racine l-ième du fibré canonique). Ces espaces ont la propriété que la transition au type générale se produit à un genre inférieur. Dans ce travail nous voulons généraliser cette approche de deux façons : - un étude de l'espace de modules des courbes avec une racine d'une puissance quelconque du fibré canonique ; - un étude de l'espace de modules des courbes avec un G-recouvrement pour un quelconque G groupe fini. Pour définir ces espaces de modules nous utilisons la notion de courbe twisted (voir Abramovich-Corti-Vistoli). Le résultat fondamental obtenu est qu'il est possible de décrire le lieu singulier de ces espaces de modules par la notion de graphe dual d'une courbe. Grace à cette analyse, nous pouvons developper des calculs dans l'anneau tautologique des espaces, et en particulier nous conjecturons que l'espace de modules des courbes avec un S3-recouvrement est de type générale pour genre impaire g>=13
The moduli space Mgbar of genus g stable curves is a central object in algebraic geometry. From the point of view of birational geometry, it is natural to ask if Mgbar is of general type. Harris-Mumford and Eisenbud-Harris found that Mgbar is of general type for genus g>=24 and g=22. The case g=23 keep being mysterious. In the last decade, in an attempt to clarify this, a new approach emerged: the idea is to consider finite covers of Mgbar that are moduli spaces of stable curves equipped with additional structure as l-covers (l-th roots of the trivial bundle) or l-spin bundles (l-th roots of the canonical bundle). These spaces have the property that the transition to general type happens to a lower genus. In this work we intend to generalize this approach in two ways: - a study of moduli space of curves with any root of any power of the canonical bundle; - a study of the moduli space of curves with G-covers for any finite group G. In order to define these moduli spaces we use the notion of twisted curve (see Abramovich-Corti-Vistoli). The fundamental result obtained is that it is possible to describe the singular locus of these moduli spaces via the notion of dual graph of a curve. Thanks to this analysis, we are able to develop calculations on the tautological rings of the spaces, and in particular we conjecture that the moduli space of curves with S3-covers is of general type for odd genus g>=13

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Belotto, Da Silva André Ricardo. "Resolution of singularities in foliated spaces." Phd thesis, Université de Haute Alsace - Mulhouse, 2013. http://tel.archives-ouvertes.fr/tel-00909798.

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Let M be an analytic manifold over the real or complex field, J be a coherent and everywhere non-zero ideal sheaf over M, E be a reduced SNC divisor and Θ an involutive singular distribution everywhere tangent to E. The main objective of this work is to obtain a resolution of singularities for the ideal sheaf J that preserves some ''good" properties of the singular distribution Θ. More precisely, the R-monomial property : the existence of local monomial first integrals. This problem arises naturally when we study the ''interaction" between a variety and a foliation and, thus, is also related with the problem of monomialization of maps and of ''quasi-smooth" resolution of families of ideal sheaves.- The first result is a global resolution if the ideal sheaf J is invariant by the singular distribution Θ;- The second result is a global resolution if the the singular distribution Θ has leaf dimension 1;- The third result is a local uniformization if the the singular distribution Θ has leaf dimension 2;We also present two applications of the previous results. The first application concerns the resolution of singularities in families, either of ideal sheaves or vector fields. For the second application, we apply the results to a dynamical system problem motivated by a question of Mattei.

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Antonakoudis, Stergios M. "The complex geometry of Teichmüller space." Thesis, Harvard University, 2014. http://dissertations.umi.com/gsas.harvard:11637.

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We study isometric maps between Teichmüller spaces and bounded symmetric domains in their Kobayashi metric. We prove that every totally geodesic isometry from a disk to Teichmüller space is either holomorphic or anti-holomorphic; in particular, it is a Teichmüller disk. However, we prove that in dimensions two or more there are no holomorphic isometric immersions between Teichmüller spaces and bounded symmetric domains and also prove a similar result for isometric submersions.
Mathematics

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Krylov, Igor. "Birational geometry of Fano fibrations." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28857.

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An algebraic variety is called rationally connected if two generic points can be connected by a curve isomorphic to the projective line. The output of the minimal model program applied to rationally connected variety is variety admitting Mori fiber spaces over a rationally connected base. In this thesis we study the birational geometry of a particular class of rationally connected Mori fiber spaces: Fano fibrations over the projective line. We construct examples of Fano fibrations with a unique Mori fiber space in their birational classes. We prove that these examples are not birational to varieties of Fano type, thus answering the question of Cascini and Gongyo. That is we prove that the classes of rationally connected varieties and varieties of Fano type are not birationally equivalent. To construct the examples we use the techniques of birational rigidity. A Mori fiber space is called birationally rigid if there is a unique Mori fiber space structure in its birational class. The birational rigidity of smooth varieties admitting a del Pezzo fibration of degrees 1 and 2 is a well studied question. Unfortunately it is not enough to study smooth del Pezzo fibrations as there are fibrations which do not have smooth or even smoothable minimal models. In the case of fibrations of degree 2 we know that there is a minimal model with 2-Gorenstein singularities. These singularities are degenerations of the simplest terminal quotient singularity: singular points of the type 1/2(1,1,1). We give first examples of birationally rigid del Pezzo fibrations with 2-Gorenstein singularities. We then apply this result to study finite subgroups of the Cremona group of rank three. We then study the birational geometry of Fano fibrations from a different side. Using the reduction to characteristic 2 method we prove that double covers of Pn-bundles over Pm branched over a divisor of sufficiently high degree are not stably rational. For a del Pezzo fibration Y→P1 of degree 2 such that X is smooth there is a double cover Y→ X, where X is a P2-bundle over P1. In this case a stronger result holds: a very general Y with Pic(Y)≅Z⊕Z is not stably rational. We discuss the proof of this statement.

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Liu, Stephen Shang Yi. "On the Asymptotic Behavior of the Magnitude Function for Odd-dimensional Euclidean Balls." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1585399513964864.

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Montcouquiol, Grégoire. "Déformations de métriques Einstein sur des variétés à singularités coniques." Toulouse 3, 2005. http://www.theses.fr/2005TOU30205.

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Partant d'une cône-variété hyperbolique compacte de dimension n>2, on étudie les déformations de la métrique dans le but d'obtenir des cônes-variétés Einstein. Dans le cas où le lieu singulier est une sous-variété fermée de codimension 2 et que tous les angles coniques sont plus petits que 2pi, on montre qu'il n'existe pas de déformations Einstein infinitésimales non triviales préservant les angles coniques. Ce résultat peut s'interpréter comme une généralisation en dimension supérieure du célèbre théorème de Hodgson et Kerckhoff sur les déformations des cônes-variétés hyperboliques de dimension 3. Si tous les angles coniques sont inférieurs à pi, on donne ensuite une construction qui à chaque variation donnée des angles associe une déformation Einstein infinitésimale correspondante
Starting with a compact hyperbolic cone-manifold of dimension n>2, we study the deformations of the metric in order to get Einstein cone-manifolds. If the singular locus is a closed codimension 2 submanifold and all cone angles are smaller than 2pi, we show that there is no non-trivial infinitesimal Einstein deformations preserving the cone angles. This result can be interpreted as a higher-dimensional case of the celebrated Hodgson and Kerckhoff's theorem on deformations of hyperbolic 3-cone-manifolds. If all cone angles are smaller than pi, we also give a construction which associates to any variation of the angles a corresponding infinitesimal Einstein deformation

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Russell, Neil Eric. "Aspects of the symplectic and metric geometry of classical and quantum physics." Thesis, Rhodes University, 1993. http://hdl.handle.net/10962/d1005237.

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I investigate some algebras and calculi naturally associated with the symplectic and metric Clifford algebras. In particular, I reformulate the well known Lepage decomposition for the symplectic exterior algebra in geometrical form and present some new results relating to the simple subspaces of the decomposition. I then present an analogous decomposition for the symmetric exterior algebra with a metric. Finally, I extend this symmetric exterior algebra into a new calculus for the symmetric differential forms on a pseudo-Riemannian manifold. The importance of this calculus lies in its potential for the description of bosonic systems in Quantum Theory.

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Welly, Adam. "The Geometry of quasi-Sasaki Manifolds." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20466.

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Let (M,g) be a quasi-Sasaki manifold with Reeb vector field xi. Our goal is to understand the structure of M when g is an Einstein metric. Assuming that the S^1 action induced by xi is locally free or assuming a certain non-negativity condition on the transverse curvature, we prove some rigidity results on the structure of (M,g). Naturally associated to a quasi-Sasaki metric g is a transverse Kahler metric g^T. The transverse Kahler-Ricci flow of g^T is the normalized Ricci flow of the transverse metric. Exploiting the transverse Kahler geometry of (M,g), we can extend results in Kahler-Ricci flow to our transverse version. In particular, we show that a deep and beautiful theorem due to Perleman has its counterpart in the quasi-Sasaki setting. We also consider evolving a Sasaki metric g by Ricci flow. Unfortunately, if g(0) is Sasaki then g(t) is not Sasaki for t>0. However, in some instances g(t) is quasi-Sasaki. We examine this and give some qualitative results and examples in the special case that the initial metric is eta-Einstein.

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SARACCO, FABIO. "Patching up II A singularities." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2013. http://hdl.handle.net/10281/40053.

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In the context of supergravity, the Romans mass is a scalar flux which has been shown to have peculiar properties as avoiding uplifting to M-theory; moreover, in several models it has been used in order to fix moduli. We show that the singularity in SuperGravity due to the O6 plane, that for a vanishing Romas mass is resolved in M-theory, is canceled by the presence of the Romans mass. The result has been obtained using the Generalized Complex Geometry formalism in SuperGravity. The same phenomenon is shown from the gauge theory point of view: the metric near the O6 in the massless case is the moduli space of the Seiberg-Witten model reduced to 3 dimensions. The deformation induced by the Romans mass is introduced by a Chern-Simons term in the Lagrangian.

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StClair, Jessica Lindsey. "Geometry of Spaces of Planar Quadrilaterals." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26887.

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The purpose of this dissertation is to investigate the geometry of spaces of planar quadrilaterals. The topology of moduli spaces of planar quadrilaterals (the set of all distinct planar quadrilaterals with fixed side lengths) has been well-studied [5], [8], [10]. The symplectic geometry of these spaces has been studied by Kapovich and Millson [6], but the Riemannian geometry of these spaces has not been thoroughly examined. We study paths in the moduli space and the pre-moduli space. We compare intraplanar paths between points in the moduli space to extraplanar paths between those same points. We give conditions on side lengths to guarantee that intraplanar motion is shorter between some points. Direct applications of this result could be applied to motion-planning of a robot arm. We show that horizontal lifts to the pre-moduli space of paths in the moduli space can exhibit holonomy. We determine exactly which collections of side lengths allow holonomy.
Ph. D.

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33

Yoshino, Masaki. "An L²‐index formula for monopoles with Dirac-type singularities." Kyoto University, 2020. http://hdl.handle.net/2433/253069.

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Fankhänel, Andreas. "Metrical Problems in Minkowski Geometry." Doctoral thesis, Universitätsbibliothek Chemnitz, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-95007.

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In this dissertation we study basic metrical properties of 2-dimensional normed linear spaces, so-called (Minkowski or) normed planes. In the first chapter we introduce a notion of angular measure, and we investigate under what conditions certain angular measures in a Minkowski plane exist. We show that only the Euclidean angular measure has the property that in an isosceles triangle the base angles are of equal size. However, angular measures with the property that the angle between orthogonal vectors has a value of pi/2, i.e, a quarter of the full circle, exist in a wider variety of normed planes, depending on the type of orthogonality. Due to this we have a closer look at isosceles and Birkhoff orthogonality. Finally, we present results concerning angular bisectors. In the second chapter we pay attention to convex quadrilaterals. We give definitions of different types of rectangles and rhombi and analyse under what conditions they coincide. Combinations of defining properties of rectangles and rhombi will yield squares, and we will see that any two types of squares are equal if and only if the plane is Euclidean. Additionally, we define a ``new\'\' type of quadrilaterals, the so-called codises. Since codises and rectangles coincide in Radon planes, we will explain why it makes sense to distinguish these two notions. For this purpose we introduce the concept of associated parallelograms. Finally we will deal with metrically defined conics, i.e., with analogues of conic sections in normed planes. We define metric ellipses (hyperbolas) as loci of points that have constant sum (difference) of distances to two given points, the so-called foci. Also we define metric parabolas as loci of points whose distance to a given point equals the distance to a fixed line. We present connections between the shape of the unit ball B and the shape of conics. More precisely, we will see that straight segments and corner points of B cause, under certain conditions, that conics have straight segments and corner points, too. Afterwards we consider intersecting ellipses and hyperbolas with identical foci. We prove that in special Minkowski planes, namely in the subfamily of polygonal planes, confocal ellipses and hyperbolas intersect in a way called Birkhoff orthogonal, whenever the respective ellipse is large enough.

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Yu, Jianming. "Kombinatorische Geometrie der Stokesregionen." Bonn : [s.n.], 1990. http://catalog.hathitrust.org/api/volumes/oclc/23006551.html.

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Le, Thanh Tam. "Geometry-Aware Learning Algorithms for Histogram Data Using Adaptive Metric Embeddings and Kernel Functions." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/204594.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(情報学)
甲第19417号
情博第596号
新制||情||104(附属図書館)
32442
京都大学大学院情報学研究科知能情報学専攻
(主査)教授山本章博, 教授黒橋禎夫, 教授鹿島久嗣, 准教授 Cuturi Marco
学位規則第4条第1項該当

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Lapp, Frank. "An index theorem for operators with horn singularities." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät II, 2013. http://dx.doi.org/10.18452/16838.

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Die abgeschlossenen Erweiterungen der sogenannten geometrischen Operatoren (Spin-Dirac, Gauß-Bonnet und Signatur-Operator) auf Mannigfaltigkeiten mit metrischen Hörnern sind Fredholm-Operatoren und ihr Index wurde von Matthias Lesch, Norbert Peyerimhoff und Jochen Brüning berechnet. Es wurde gezeigt, dass die Einschränkungen dieser drei Operatoren auf eine punktierte Umgebung des singulären Punkts unitär äquivalent zu irregulär singulären Operator-wertigen Differentialoperatoren erster Ordnung sind. Die Lösungsoperatoren der dazugehörigen Differentialgleichungen definierten eine Parametrix, mit deren Hilfe die Fredholmeigenschaft bewiesen wurde. In der vorliegenden Doktorarbeit wird eine Klasse von irregulären singulären Differentialoperatoren erster Ordnung, genannt Horn-Operatoren, eingeführt, die die obigen Beispiele verallgemeinern. Es wird bewiesen, dass ein elliptischer Differentialoperator erster Ordnung, dessen Einschränkung auf eine punktierte Umgebung des singulären Punkts unitär äquivalent zu einem Horn-Operator ist, Fredholm ist, und sein Index wird berechnet. Schließlich wird dieser abstrakte Index-Satz auf geometrische Operatoren auf Mannigfaltigkeiten mit "multiply warped product"-Singularitäten angewendet, welche eine wesentliche Verallgemeinerung der metrischen Hörner darstellen.
The closed extensions of geometric operators (Spin-Dirac, Gauss-Bonnet and Signature operator) on a manifold with metric horns are Fredholm operators, and their indices were computed by Matthias Lesch, Norbert Peyerimhoff and Jochen Brüning. It was shown that the restrictions of all three operators to a punctured neighbourhood of the singular point are unitary equivalent to a class of irregular singular operator-valued differential operators of first order. The solution operators of the corresponding differential equations defined a parametrix which was applied to prove the Fredholm property. In this thesis a class of irregular singular differential operators of first order - called horn operators - is introduced that extends the examples mentioned above. It is proved that an elliptic differential operator of first order whose restriction to the neighbourhood of the singular point is unitary equivalent to a horn operator is Fredholm and its index is computed. Finally, this abstract index theorem is applied to compute the indices of geometric operators on manifolds with multiply warped product singularities that extend the notion of metric horns considerably.

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Le, Brigant Alice. "Probability on the spaces of curves and the associated metric spaces via information geometry; radar applications." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0640/document.

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Nous nous intéressons à la comparaison de formes de courbes lisses prenant leurs valeurs dans une variété riemannienne M. Dans ce but, nous introduisons une métrique riemannienne invariante par reparamétrisations sur la variété de dimension infinie des immersions lisses dans M. L’équation géodésique est donnée et les géodésiques entre deux courbes sont construites par tir géodésique. La structure quotient induite par l’action du groupe des reparamétrisations sur l’espace des courbes est étudiée. À l’aide d’une décomposition canonique d’un chemin dans un fibré principal, nous proposons un algorithme qui construit la géodésique horizontale entre deux courbes et qui fournit un matching optimal. Dans un deuxième temps, nous introduisons une discrétisation de notre modèle qui est elle-même une structure riemannienne sur la variété de dimension finie Mn+1 des "courbes discrètes" définies par n + 1 points, où M est de courbure sectionnelle constante. Nous montrons la convergence du modèle discret vers le modèle continu, et nous étudions la géométrie induite. Des résultats de simulations dans la sphère, le plan et le demi-plan hyperbolique sont donnés. Enfin, nous donnons le contexte mathématique nécessaire à l’application de l’étude de formes dans une variété au traitement statistique du signal radar, où des signaux radars localement stationnaires sont représentés par des courbes dans le polydisque de Poincaré via la géométrie de l’information
We are concerned with the comparison of the shapes of open smooth curves that take their values in a Riemannian manifold M. To this end, we introduce a reparameterization invariant Riemannian metric on the infinite-dimensional manifold of these curves, modeled by smooth immersions in M. We derive the geodesic equation and solve the boundary value problem using geodesic shooting. The quotient structure induced by the action of the reparametrization group on the space of curves is studied. Using a canonical decomposition of a path in a principal bundle, we propose an algorithm that computes the horizontal geodesic between two curves and yields an optimal matching. In a second step, restricting to base manifolds of constant sectional curvature, we introduce a detailed discretization of the Riemannian structure on the space of smooth curves, which is itself a Riemannian metric on the finite-dimensional manifold Mn+1 of "discrete curves" given by n + 1 points. We show the convergence of the discrete model to the continuous model, and study the induced geometry. We show results of simulations in the sphere, the plane, and the hyperbolic halfplane. Finally, we give the necessary framework to apply shape analysis of manifold-valued curves to radar signal processing, where locally stationary radar signals are represented by curves in the Poincaré polydisk using information geometry

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Ouwehand, David. "Local rigid cohomology of weighted homogeneous hypersurface singularities." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17732.

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Das Ziel dieser Dissertation ist die Erforschung einer gewissen Invariante von Singularitäten über einem Grundkörper k von positiver Charakteristik. Sei x \in X ein singulärer Punkt auf einem k-Schema. Dann ist die lokale rigide Kohomologie im Grad i definiert als H^i_{rig, {x}}(X), also als die rigide Kohomologie von X mit Träger in der Teilmenge {x}. In Kapitel 2 zeigen wir, dass die lokale rigide Kohomologie tatsächlich eine Invariante ist. Das heißt: Sind x'' \in X'' und x \in X kontaktäquivalente singuläre Punkte auf k-Schemata, dann sind die Vektorräume H_{rig, {x}}(X) und H_{rig, {x''}}(X'') zueinander isomorph. Dieser Isomorphismus ist kompatibel mit der Wirkung des Frobenius auf der rigiden Kohomologie. In den Kapiteln 3 und 4 beschäftigen wir uns mit gewichtet homogenen Singularitäten von Hyperflächen. Der Hauptsatz des dritten Kapitels besagt, dass die lokale rigide Kohomologie einer solchen Singularität isomorph ist zu dem G-invarianten Teil von H_{rig}(\Proj^{n-1}_k \setminus \widetilde{S}_{\infty}). Hier bezeichnet \widetilde{S}_{\infty} \subset \Proj^{n-1}_k eine gewisse glatte projektive Hyperfläche und G ist eine endliche Gruppe, die auf der rigiden Kohomologie des Komplements wirkt. Dank einem Algorithmus von Abbott, Kedlaya und Roe ist es möglich, den Frobenius-Automorphismus auf H_{rig}(\Proj^{n-1}_k \setminus \widetilde{S}_{\infty}) annähernd zu berechnen. In Kapitel 4 formulieren wir eine Anpassung dieses Algorithmus, mithilfe derer Berechnungen auf dem G-invarianten Teil gemacht werden können. Der angepasste Algorithmus kann vollständig mithilfe gewichtet homogener Polynome formuliert werden, was für unsere Anwendungen sehr natürlich scheint. In Kapitel 5 formulieren wir einige Vermutungen und offene Probleme, die mit den Ergebnissen der früheren Kapitel zusammenhängen.
The goal of this thesis is to study a certain invariant of isolated singularities over a base field k of positive characteristic. This invariant is called the local rigid cohomology. For a singular point x \in X on a k-scheme, the i-th local rigid cohomology is defined as H^i_{rig, {x}}(X), the i-th rigid cohomology of X with supports in the subset {x}. In chapter 2 we show that the local rigid cohomology is indeed an invariant. That is: if x'' \in X'' and x \in X are contact-equivalent singularities on k-schemes, then the local rigid cohomology spaces H_{rig, {x}}(X) and H_{rig, {x''}}(X'') are isomorphic. The isomorphism that we construct is moreover compatible with the Frobenius action on rigid cohomology. In chapters 3 and 4 we focus our attention on weighted homogeneous hypersurface singularities. Our goal in chapter 3 is to show that for such a singularity, the local rigid cohomology may be identified with the G-invariants of a certain rigid cohomology space $H_{rig}(\Proj^{n-1}_k \setminus \widetilde{S}_{\infty}). Here \widetilde{S}_{\infty} \subset \Proj^{n-1}_k is a smooth projective hypersurface, and G is a certain finite group acting on the rigid cohomology of its complement. It is known that the rigid cohomology of a smooth projective hypersurface is amenable to direct computation. Indeed, an algorithm by Abbott, Kedlaya and Roe allows one to approximate the Frobenius on such a rigid cohomology space. In chapter 4 we will modify this algorithm to deal with the G-invariant part of cohomology. The modified algorithm can be formulated entirely in terms of weighted homogeneous polynomials, which seems natural for our applications. Chapter 5 is a collection of conjectures and open problems that are related to the earlier chapters.

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Suleymanova, Asilya [Verfasser], Jochen [Gutachter] Bruening, Julie [Gutachter] Rowlett, and Klaus [Gutachter] Kirsten. "On the spectral geometry of manifolds with conic singularities / Asilya Suleymanova ; Gutachter: Jochen Bruening, Julie Rowlett, Klaus Kirsten." Berlin : Humboldt-Universität zu Berlin, 2017. http://d-nb.info/1185579370/34.

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41

Lesser, Alice. "Optimal and Hereditarily Optimal Realizations of Metric Spaces." Doctoral thesis, Uppsala University, Department of Mathematics, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8297.

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This PhD thesis, consisting of an introduction, four papers, and some supplementary results, studies the problem of finding an optimal realization of a given finite metric space: a weighted graph which preserves the metric's distances and has minimal total edge weight. This problem is known to be NP-hard, and solutions are not necessarily unique.

It has been conjectured that extremally weighted optimal realizations may be found as subgraphs of the hereditarily optimal realization Γ_d, a graph which in general has a higher total edge weight than the optimal realization but has the advantages of being unique, and possible to construct explicitly via the tight span of the metric.

In Paper I, we prove that the graph Γ_d is equivalent to the 1-skeleton of the tight span precisely when the metric considered is totally split-decomposable. For the subset of totally split-decomposable metrics known as consistent metrics this implies that Γ_d is isomorphic to the easily constructed Buneman graph.

In Paper II, we show that for any metric on at most five points, any optimal realization can be found as a subgraph of Γ_d.

In Paper III we provide a series of counterexamples; metrics for which there exist extremally weighted optimal realizations which are not subgraphs of Γ_d. However, for these examples there also exists at least one optimal realization which is a subgraph.

Finally, Paper IV examines a weakened conjecture suggested by the above counterexamples: can we always find some optimal realization as a subgraph in Γ_d? Defining extremal optimal realizations as those having the maximum possible number of shortest paths, we prove that any embedding of the vertices of an extremal optimal realization into Γ_d is injective. Moreover, we prove that this weakened conjecture holds for the subset of consistent metrics which have a 2-dimensional tight span

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Prandi, Dario. "Geometry and analysis of control-affine systems: motion planning, heat and Schrödinger evolution." Doctoral thesis, SISSA, 2014. http://hdl.handle.net/20.500.11767/3913.

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This thesis is dedicated to two problems arising from geometric control theory, regarding control-affine systems $\dot q= f_0(q)+\sum_{j=1}^m u_j f_j(q)$, where $f_0$ is called the drift. In the first part we extend the concept of complexity of non-admissible trajectories, well understood for sub-Riemannian systems, to this more general case, and find asymptotic estimates. In order to do this, we also prove a result in the same spirit as the Ball-Box theorem for sub-Riemannian systems, in the context of control-affine systems equipped with the L1 cost. Then, in the second part of the thesis, we consider a family of 2-dimensional driftless control systems. For these, we study how the set where the control vector fields become collinear affects the diffusion dynamics. More precisely, we study whether solutions to the heat and Schrödinger equations associated with this Laplace-Beltrami operator are able to cross this singularity, and how its the presence affects the spectral properties of the operator, in particular under a magnetic Aharonov–Bohm-type perturbation.

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Imagi, Yohsuke. "Surjectivity of a Gluing for Stable T2-cones in Special Lagrangian Geometry." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/189337.

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Simsir, Muazzez Fatma. "Conformal Vector Fields With Respect To The Sasaki Metric Tensor Field." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12605857/index.pdf.

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On the tangent bundle of a Riemannian manifold the most natural choice of metric tensor field is the Sasaki metric. This immediately brings up the question of infinitesimal symmetries associated with the inherent geometry of the tangent bundle arising from the Sasaki metric. The elucidation of the form and the classification of the Killing vector fields have already been effected by the Japanese school of Riemannian geometry in the sixties. In this thesis we shall take up the conformal vector fields of the Sasaki metric with the help of relatively advanced techniques.

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Saha, Abhijoy. "A Geometric Framework for Modeling and Inference using the Nonparametric Fisher–Rao metric." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1562679374833421.

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Wells, Clive Gene. "The application of differential geometry to classical and quantum gravity." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/283187.

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Wink, Matthias. "Ricci solitons and geometric analysis." Thesis, University of Oxford, 2018. http://ora.ox.ac.uk/objects/uuid:3aae2c5e-58aa-42da-9a1b-ec15cacafdad.

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This thesis studies Ricci solitons of cohomogeneity one and uniform Poincaré inequalities for differentials on Riemann surfaces. In the two summands case, which assumes that the isotropy representation of the principal orbit consists of two inequivalent Ad-invariant irreducible summands, complete steady and expanding Ricci solitons have been detected numerically by Buzano-Dancer-Gallaugher-Wang. This work provides a rigorous construction thereof. A Lyapunov function is introduced to prove that the Ricci soliton metrics lie in a bounded region of an associated phase space. This also gives an alternative construction of non-compact Einstein metrics of non-positive scalar curvature due to Böhm. It is explained how the asymptotics of the Ricci flat trajectories induce Böhm's Einstein metrics on spheres and other low dimensional spaces. A numerical study suggests that all other Einstein metrics of positive scalar curvature which are induced by the generalised Hopf fibrations occur in an entirely non-linear regime of the Einstein equations. Extending the theory of cohomogeneity one steady and expanding Ricci solitons, an estimate which allows to prescribe the growth rate of the soliton potential at any given time is shown. As an application, continuous families of Ricci solitons on complex line bundles over products of Fano Kähler Einstein manifolds are constructed. This generalises work of Appleton and Stolarski. The method also applies to the Lü-Page-Pope set-up and allows to cover an optimal parameter range in the two summands case. The Ricci soliton equation on manifolds foliated by torus bundles over products of Fano Kähler Einstein manifolds is discussed. A rigidity theorem is obtained and a preserved curvature condition is discovered. The cohomogeneity one initial value problem is solved for m-quasi-Einstein metrics and complete metrics are described. L^p-Poincaré inequalities for k-differentials on closed Riemann surfaces are shown. The estimates are uniform in the sense that the Poincaré constant only depends on p &GE;1, k ≥ 2 and the genus γ ≥ 2 of the surface but not on its complex structure. Examples show that the analogous estimate for 1-differentials cannot be uniform. This part is based on joint work with Melanie Rupflin.

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Tewodrose, David. "Some functional inequalities and spectral properties of metric measure spaces with curvature bounded below." Doctoral thesis, Scuola Normale Superiore, 2018. http://hdl.handle.net/11384/85734.

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[from the introduction]: The aim of this thesis is to study metric measure spaces with a synthetic notion of Ricci curvature bounded below. We study them from the point of view of Sobolev/Nash type functional inequalities in the non-compact case, and from the point of view of spectral analysis in the compact case. The heat kernel links the two cases: in the first one, the goal is to get new estimates on the heat kernel of some associated weighted structure; in the second one, the heat kernel is the basic tool to establish our results. The topic of synthetic Ricci curvature bounds has known a constant development over the past few years. In this introduction, we shall give some historical account on this theory, before explaining in few words the content of this work. The letter K will refer to an arbitrary real number and N will refer to any finite number greater or equal than 1.

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Enders, Joerg. "Generalizations of the reduced distance in the Ricci flow - monotonicity and applications." Diss., Connect to online resource - MSU authorized users, 2008.

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at, Andreas Cap@esi ac. "Parabolic Geometries, CR-Tractors, and the Fefferman Construction." ESI preprints, 2001. ftp://ftp.esi.ac.at/pub/Preprints/esi1084.ps.

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Dissertations / Theses on the topic 'Metric geometry of singularities'

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