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Excluding Infinite Clique Minors by Neil Robertson,Paul D. Seymour,Robin Thomas Pdf
Two of the authors proved a well-known conjecture of K. Wagner, that in any infinite set of finite graphs there are two graphs so that one is a minor of the other. A key lemma was a theorem about the structure of finite graphs that have no $K_n$ minor for a fixed integer $n$. Here, the authors obtain an infinite analog of this lemma--a structural condition on a graph, necessary and sufficient for it not to contain a $K_n$ minor, for any fixed infinite cardinal $n$.
Directions in Infinite Graph Theory and Combinatorics by R. Diestel Pdf
This book has arisen from a colloquium held at St. John's College, Cambridge, in July 1989, which brought together most of today's leading experts in the field of infinite graph theory and combinatorics. This was the first such meeting ever held, and its aim was to assess the state of the art in the discipline, to consider its links with other parts of mathematics, and to discuss possible directions for future development. This volume reflects the Cambridge meeting in both level and scope. It contains research papers as well as expository surveys of particular areas. Together they offer a comprehensive portrait of infinite graph theory and combinatorics, which should be particularly attractive to anyone new to the discipline.
Integrable Systems and Riemann Surfaces of Infinite Genus by Martin Ulrich Schmidt Pdf
This memoir develops the spectral theory of the Lax operators of nonlinear Schrodinger-like partial differential equations with periodic boundary conditions. Their spectral curves, i.e., the common spectrum with the periodic shifts, are generically Riemann surfaces of infinite genus. The points corresponding to infinite energy are added. The resulting spaces are no longer Riemann surfaces in the usual sense, but they are quite similar to compact Riemann surfaces. In fact, some of the basic tools of the theory of compact Riemann surfaces are generalized to these spectral curves and illuminate the structure of complete integrability: The eigen bundles define holomorphic line bundles on the spectral curves, which completely determine the potentials. These line bundles may be described by divisors of the same degree as the genus, and these divisors give rise to Darboux coordinates. With the help of a Riemann-Roch Theorem, the isospectral sets (the sets of all potentials corresponding to the same spectral curve) may be identified with open dense subsets of the Jacobian varieties. The real parts of the isospectral sets are infinite dimensional tori, and the group action solves the corresponding nonlinear partial differential equations. Deformations of the spectral curves are in one to one correspondence with holomorphic forms. Serre Duality reproduces the symplectic form.
In this book, the author studies the Dirichlet series whose coefficients are the number of orders of a quartic field with given indices. Nakagawa gives an explicit expression of the Dirichlet series. Using this expression, its analytic properties are deduced. He also presents an asymptotic formula for the number of orders in a quartic field with index less than a given positive number.
The Fundamental Lemma for the Shalika Subgroup of $GL(4)$ by Solomon Friedberg,Hervé Jacquet Pdf
The authors establish the fundamental lemma for a relative trace formula. The trace formula compares generic automorphic representations of [italic capitals]GS[italic]p(4) with automorphic representations of [italic capitals]GS(4) which are distinguished with respect to a character of the Shalika subgroup, the subgroup of matrices of 2 x 2 block form ([superscript italic]g [over] [subscript capital italic]X [and] 0 [over] [superscript italic]g). The fundamental lemma, giving the equality of the orbital integrals of the unit elements of the respective Hecke algebras, amounts to a comparison of certain exponential sums arising from these two different groups.
Stratifying Endomorphism Algebras by Edward Cline,Brian Parshall,Leonard Scott,Leonard L. Scott Pdf
Suppose that $R$ is a finite dimensional algebra and $T$ is a right $R$-module. Let $A = \mathrm{ End}_R(T)$ be the endomorphism algebra of $T$. This memoir presents a systematic study of the relationships between the representation theories of $R$ and $A$, especially those involving actual or potential structures on $A$ which ''stratify'' its homological algebra. The original motivation comes from the theory of Schur algebras and the symmetric group, Lie theory, and the representation theory of finite dimensional algebras and finite groups. The book synthesizes common features of many of the above areas, and presents a number of new directions. Included are an abstract ''Specht/Weyl module'' correspondence, a new theory of stratified algebras, and a deformation theory for them. The approach reconceptualizes most of the modular representation theory of symmetric groups involving Specht modules and places that theory in a broader context. Finally, the authors formulate some conjectures involving the theory of stratified algebras and finite Coexeter groups, aiming toward understanding the modular representation theory of finite groups of Lie type in all characteristics.
Symmetric Automorphisms of Free Products by Darryl McCullough,Andy Miller Pdf
This memoir examines the automorphism group of a group $G$ with a fixed free product decomposition $G_1*\cdots *G_n$. An automorphism is called symmetric if it carries each factor $G_i$ to a conjugate of a (possibly different) factor $G_j$. The symmetric automorphisms form a group $\Sigma Aut(G)$ which contains the inner automorphism group $Inn(G)$. The quotient $\Sigma Aut(G)/Inn(G)$ is the symmetric outer automorphism group $\Sigma Out(G)$, a subgroup of $Out(G)$. It coincides with $Out(G)$ if the $G_i$ are indecomposable and none of them is infinite cyclic. To study $\Sigma Out(G)$, the authors construct an $(n-2)$-dimensional simplicial complex $K(G)$ which admits a simplicial action of $Out(G)$. The stabilizer of one of its components is $\Sigma Out(G)$, and the quotient is a finite complex. The authors prove that each component of $K(G)$ is contractible and describe the vertex stabilizers as elementary constructs involving the groups $G_i$ and $Aut(G_i)$. From this information, two new structural descriptions of $\Sigma Aut (G)$ are obtained. One identifies a normal subgroup in $\Sigma Aut(G)$ of cohomological dimension $(n-1)$ and describes its quotient group, and the other presents $\Sigma Aut (G)$ as an amalgam of some vertex stabilizers. Other applications concern torsion and homological finiteness properties of $\Sigma Out (G)$ and give information about finite groups of symmetric automorphisms. The complex $K(G)$ is shown to be equivariantly homotopy equivalent to a space of $G$-actions on $\mathbb R$-trees, although a simplicial topology rather than the Gromov topology must be used on the space of actions.
The Operator Hilbert Space $OH$, Complex Interpolation and Tensor Norms by Gilles Pisier Pdf
In the recently developed duality theory of operator spaces (as developed by Effros-Ruan and Blecher-Paulsen) bounded operators are replaced by completely bounded ones, isomorphisms by complete isomorphisms, and Banach spaces by operator spaces. This allows for distinguishing between the various ways in which a given Banach space can be embedded isometrically into $B(H)$ (with $H$ being Hilbert). In this new category, several operator spaces which are isomorphic (as Banach spaces) to a Hilbert space play an important role. For instance the row and column Hilbert spaces and several other examples appearing naturally in the construction of the Boson or Fermion Fock spaces have been studied extensively. One of the main results of this memoir is the observation that there is a central object in this class: there is a unique self dual Hilbertian operator space (denoted by $OH$ ) which seems to play the same central role in the category of operator spaces that Hilbert spaces play in the category of Banach spaces. This new concept, called ``the operator Hilbert space'' and denoted by $OH$, is introduced and thoroughly studied in this volume.
The Structure of $k$-$CS$- Transitive Cycle-Free Partial Orders by Richard Warren Pdf
The class of cycle-free partial orders (CFPOs) is defined, and the CFPOs fulfilling a natural transitivity assumption, called $k$-connected set transitivity ($k$-$CS$-transitivity), are analyzed in some detail. Classification in many of the interesting cases is given. This work generalizes Droste's classification of the countable $k$-transitive trees ($k \geq 2$). In a CFPO, the structure can branch downwards as well as upwards, and can do so repeatedly (though it never returns to the starting point by a cycle). Mostly it is assumed that $k \geq 3$ and that all maximal chains are finite. The main classification splits into the sporadic and skeletal cases. The former is complete in all cardinalities. The latter is performed only in the countable case. The classification is considerably more complicated than for trees, and skeletal CFPOs exhibit rich, elaborate and rather surprising behavior. Features: Lucid exposition of an important generalization of Droste's work Extended introduction clearly explaining the scope of the memoir Visually attractive topic with copious illustrations Self-contained material, requiring few prerequisites
Some Connections between Isoperimetric and Sobolev-type Inequalities by Serguei Germanovich Bobkov,Christian Houdré Pdf
For Borel probability measures on metric spaces, this text studies the interplay between isoperimetric and Sobolev-type inequalities. In particular the question of finding optimal constants via isoperimetric quantities is explored. Also given are necessary and sufficient conditions for the equivalence between the extremality of some sets in the isoperimetric problem and the validity of some analytic inequalities. The book devotes much attention to: the probability distributions on the real line; the normalized Lebesgue measure on the Euclidean sheres; and the canonical Gaussian measure on the Euclidean space.
Relations Related to Betweenness: Their Structure and Automorphisms by Samson Adepoju Adeleke,P. M. Neumann Pdf
This volume is about tree-like structures, namely semilinear ordering, general betweenness relations, $C$-relations and $D$-relations. It contains a systematic study of betweenness and introduces $C$ and $D$-relations to describe the behavior of points at infinity ('leaves' or 'ends' or 'directions') of trees. The focus is on structure theorems and on automorphism groups, with applications to the theory of infinite permutation groups. This work: offers the first systematic treatment of betweenness relations; introduces important new concepts of $C$-relations and $D$-relations; elucidates the close relationships between semilinear orderings, betweenness relations, $C$ and $D$-relations; and, considers their automorphism groups as important examples of Jordan permutation groups.
Two Classes of Riemannian Manifolds Whose Geodesic Flows Are Integrable by Kazuyoshi Kiyohara Pdf
In this work, two classes of manifolds whose geodesic flows are integrable are defined, and their global structures are investigated. They are called Liouville manifolds and Kahler-Liouville manifolds respectively. In each case, the author finds several invariants with which they are partly classified. The classification indicates, in particular, that these classes contain many new examples of manifolds with integrable geodesic flow.
Higher Multiplicities and Almost Free Divisors and Complete Intersections by James Damon Pdf
Almost free divisors and complete intersections form a general class of nonisolated hypersurface and completer intersection singularities. They also include discriminants of mappings, bifurcation sets, and certain types of arrangements of hyperplanes such as Coxeter arrangements and generic arrangements. Associated to the singularities of this class is a "singular Milnor fibration" which has the same homotopy properties as the Milnor fibration for isolated singularities. This memoir deduces topological properties of singularities in a number of situations including: complements of hyperplane arrangements, various nonisolated complete intersections, nonlinear arrangements of hypersurfaces, functions on discriminants, singularities defined by compositions of functions, and bifurcation sets.
Cyclic Phenomena for Composition Operators by Paul Bourdon,Joel H. Shapiro Pdf
We undertake a systematic study of cyclic phenomena for composition operators. Our work shows that composition operators exhibit strikingly diverse types of cyclic behavior, and it connects this behavior with classical problems involving complex polynomial approximation and analytic functional equations.
A Continuum Limit of the Toda Lattice by Percy Deift,Kenneth T-R McLaughlin Pdf
In this book, the authors describe a continuum limit of the Toda ODE system, obtained by taking as initial data for the finite lattice successively finer discretizations of two smooth functions. Using the integrability of the finite Toda lattice, the authors adapt the method introduced by Lax and Levermore for the study of the small dispersion limit of the Korteweg de Vries equations to the case of the Toda lattice. A general class of initial data is considered which permits, in particular, the formation of shocks. A novel feature of the analysis in this book is an extensive use of techniques from the theory of Riemann-Hilbert problems.