The main goal of this work is to examine classes of finite groups in which normality, permutability and Sylow-permutability are transitive relations. These classes of groups are called T , PT and PST , respectively. The main focus is on direct products of T , PT and PST groups and the behavior of a collection of cyclic normal, permutable and Sylow-permutable subgroups under the intersection map. In general, a direct product of finitely many groups from one of these classes does not belong to the same class, unless the orders of the direct factors are relatively prime. Examples suggest that for solvable groups it is not required to have relatively prime orders to stay in the class. In addition, the concept of normal, permutable and S-permutable cyclic sensitivity is tied with that of Tc, PTc and PSTc groups, in which cyclic subnormal subgroups are normal, permutable or Sylow-permutable. In the process another way of looking at the Dedekind, Iwasawa and nilpotent groups is provided as well as possible interplay between direct products and the intersection map is observed.

In their recent paper ``Edge-transitive products," Hammack, Imrich, and Klavzar showed that the direct product of connected, non-bipartite graphs is edge-transitive if and only if both factors are edge-transitive, and at least one is arc-transitive. However, little is known when the product is bipartite. This thesis extends this result (in part) for the case of bipartite graphs using a new technique called "stacking." For R-thin, connected, bipartite graphs A and B, we show that A x B is arc-transitive if and only if A and B are both arc-transitive. Further, we show A x B is edge-transitive only if at least one of A, B is also edge-transitive, and give evidence that strongly suggests that in fact both factors must be edge-transitive.

We define a new graph operation called the inner power of a graph. The construction is similar to the direct power of graphs, except that factors are intertwined in such a way that certain structural properties of graphs are more clearly reflected in their inner powers. We investigate various properties of inner powers, such as connectivity, bipartiteness, and their interaction with the direct product. We explore possible connections between inner powers and the problem of cancellation over the direct product of graphs.

No description available.

This thesis generalizes to digraphs certain recent results about graphs. There are special digraphs C such that AxC is isomorphic to BxC for some pair of distinct digraphs A and B. Lovasz named these digraphs C zero-divisors and completely characterized their structure. Knowing that all directed cycles are zero-divisors, we focus on the following problem: Given any directed cycle D and any digraph A, enumerate all digraphs B such that AxD is isomorphic to BxD. From our result for cycles, we generalize to an arbitrary zero-divisor C, developing upper and lower bounds for the collection of digraphs B satisfying AxC isomorphic to BxC.

While it has been known for some time that connected non-bipartite graphs have unique prime factorizations over the direct product, the same cannot be said of bipartite graphs. This is somewhat vexing, as bipartite graphs do have unique prime factorizations over other graph products (the Cartesian product, for example). However, it is fairly easy to show that a connected bipartite graph has only one prime bipartite factor, which begs the question: is such a prime bipartite factor unique? In other words, although a connected bipartite graph may have multiple prime factorizations over the direct product, do such factorizations contain the same prime bipartite factor? It has previously been shown by Hammack that when the prime bipartite factor is K_2, this is in fact true. The goal of this paper is to prove that this is in fact true for any prime bipartite factor, provided the graph being factored is R-thin. The proof of the main result takes the same initial approach as the proof by Hammack, before moving into new territory in order to prove the final result.

A cancellation graph G is one for which given any graph C, we have G\times C\cong X\times C implies G\cong X. In this thesis, we characterize all bipartite cancellation graphs. In addition, we characterize all solutions X to G\times C\cong X\times C for bipartite G. A characterization of non-bipartite cancellation graphs is yet to be found. We present some examples of solutions X to G\times C\cong X\times C for non-bipartite G, an example of a non-bipartite cancellation graph, and a conjecture regarding non-bipartite cancellation graphs.

No description available.

Cette thèse porte sur la conjecture de Baum-Connes pour les groupes quantiques. Le but principal de ce travail est l'étude de la stabilité de la conjecture de Baum-Connes par certaines constructions de groupes quantiques discrets.Dans un premier temps, nous réalisons une étude détaillé et approfondie de la reformulation catégorielle de la conjecture de Baum-Connes d'après les travaux de R. Meyer et R. Nest. Ensuite, nous appliquons ces techniques au cas concret des groupes quantiques discrets sans torsion.Nous réalisons une étude exhaustive des produits croisés afin de pouvoir les manipuler aisément en connexion avec la conjecture de Baum-Connes. Notamment nous donnons une preuve de la propriété universelle d'un produit croisé réduit par un groupe quantique discret. Nous analysons également quelques propriétés d'importance pour le contexte de cette thèse. Mentionnons particulièrement la propriété d'associativité du produit croisé par rapport à un produit semi-direct.En s'inspirant des travaux pionniers de J. Chabert nous menons une généralisation pour les groupes quantiques discrets de la stabilité de la conjecture de Baum-Connes par rapport à un produit semi-direct. Deux propriétés d'invariance d'intérêt indépendant sont également étudiées, à savoir le phénomène de torsion et la K-moyennabilité. Nous observons que l'hypothèse sans torsion force un biproduit crosié compact à être un produit semi-direct quantique sans torsion. Ainsi, la conjecture de Baum-Connes correspondante ne fournit pas d'information remarquable dans ce cas. La stratégie générale pour mener à bien une telle généralisation consiste à définir un foncteur de “décomposition” entre les catégories de Kasparov suivant l'opération de produit semi-direct. Nous observons que cette stratégie peut être extrapolée à d'autres constructions de groupes quantiques. Notamment un produit direct de groupe quantiques. Dans ce cas, nous établissons une connexion avec la formule de Künneth de manière analogue à ce qui a été démontré par J. Chabert, S. Echterhoff et H. Oyono-Oyono pour les groupes localement compacts classiques. Les propriétés de torsion et de K-moyennabilité ont également été étudiées.Nous savons, grâce à R. Vergnioux and C. Voigt, que la conjecture de Baum-Connes forte est préservée par le passage aux sous-groupes quantiques discrets divisibles. Le même résultat est vrai pour la propriété de torsion forte, grâce à Y. Arano et K. De Commer. Dans ce travail nous montrons qu'aussi bien la conjecture de Baum-Connes usuelle que la propriété de torsion usuelle sont préservées par le passage aux sous-groupes quantiques discrets divisibles. La propriété de K-moyennabilité a également été étudiée.Une notable propriété de permanence inclue dans cette thèse est la stabilité de la conjecture de Baum-Connes forte par produit en couronne libre. Pour cela, nous réalisons une complète classification des actions de torsion pour un produit libre quantique, ce qui permet de donner une formulation adéquate de la conjecture de Baum-Connes forte pour un produit en couronne libre inspirés par le travail pionnier de C. Voigt. Une application majeure est un calcul explicite de K-théorie, dans trois situations pertinentes, pour le groupe quantique compact de Lemeux-Tarrago qui est monoïdallement équivalent à un produit en couronne libre. Cette propriété de stabilité pour un produit en couronne libre ainsi que les calculs de K-théorie s'intègrent dans un travail en collaboration avec A. Freslon. Pour conclure, nous nous questionnons sur les résultats obtenus afin de proposer une liste de questions, problems et objectifs que l'auteur a rencontré durant l'intégralité de la période de recherche de cette thèse et qui rassemblent quelques unes des lignes de travail pour ses projets futures de recherche / The present dissertation is focused on the Baum-Connes conjecture for quantum groups. The main purpose of this work is the study of the Baum-Connes conjecture stability under some constructions of discrete quantum groups. In a first phase, we carry out a detailed and extensive study about the categorical reformulation of the Baum-Connes conjecture according to the results of R. Meyer and R. Nest. Next, we apply these techniques to the specific case of torsion-free discrete quantum groups. We carry out an exhaustive study of crossed products in order to handle them comfortably in connexion with the Baum-Connes conjecture. Notably, we give a proof of the universal property satisfied by a reduced crossed product by a discrete quantum group. We analyze as well some important properties for this dissertation. Let us mention in particular the associativity property of the crossed product with respect to a semi-direct product. Being inspired by the pionneer work of J. Chabert, we perform a generalization for discrete quantum groups of the invariance property of the Baum-Connes conjecture under the semi-direct product construction. Two permanence properties of own interest are studied as well. Namely, the torsion-freeness and the K-amenability. We observe that the torsion-freeness assumption forces a compact bicrossed product to be a torsion-free quantum semi-direct product, so that the corresponding Baum-Connes conjecture does not give any relevant information in this case. The general strategy used to accomplish such a generalization consists in defining a “decomposition” functor between the corresponding Kasparov categories in accordance with the semi-direct product operation. Thus, we observe that this strategy can be extrapolate to other (quantum) group constructions. Namely, to a quantum direct product. In this case, we state a connexion with the Künneth formula as pointed out by J. Chabert, S. Echterhoff and H. Oyono-Oyono for classical locally compact groups. The properties of torsion-frenness and K-amenability are also analyzed. It is known, thanks to R. Vergnioux and C. Voigt, that the strong Baum-Connes conjecture is preserved by divisible discrete quantum subgroups. The same is true for the strong torsion-freeness property, thanks to Y. Arano and K. De Commer. Here we show that both the usual Baum-Connes conjecture and the usual torsion-freeness property are preserved by divisible discrete quantum subgroups. The K-amenability property is analyzed too. A notably permanence property included in this dissertation is the invariance of the strong Baum-Connes conjecture under the free wreath product construction. For this, we carry out a complete classification of torsion actions of a quantum free product, which allows to give an appropriated formulation of the strong Baum-Connes conjecture for a free wreath product inspired by the pioneer work of C. Voigt. A major application is an explicit K-theory computation, in three relevant situations, for the Lemeux-Tarrago's compact quantum group which is monoidally equivalent to a free wreath product. Both this stability property for a free wreath product and the K-theory computations are part of a collaboration work with A. Freslon. To conclude, we question ourselves about the results obtained in order to suggest a list of questions, problems and goals that the author has encountered during the whole research period of the present dissertation and that are part of his future research projects

An odd open dominating set of a graph is a subset of the graph’s vertices with the property that the open neighborhood of each vertex in the graph contains an odd number of vertices in the subset. An odd closed r-dominating set is a subset of the graph’s vertices with the property that the closed r-ball centered at each vertex in the graph contains an odd number of vertices in the subset. We first prove that the n-fold direct product of simple graphs has an odd open dominating set if and only if each factor has an odd open dominating set. Secondly, we prove that the n-fold strong product of simple graphs has an odd closed r-dominating set if and only if each factor has an odd closed r-dominating set.