457 research outputs found
Benchmark Graphs for Practical Graph Isomorphism
The state-of-the-art solvers for the graph isomorphism problem can readily
solve generic instances with tens of thousands of vertices. Indeed, experiments
show that on inputs without particular combinatorial structure the algorithms
scale almost linearly. In fact, it is non-trivial to create challenging
instances for such solvers and the number of difficult benchmark graphs
available is quite limited. We describe a construction to efficiently generate
small instances for the graph isomorphism problem that are difficult or even
infeasible for said solvers. Up to this point the only other available
instances posing challenges for isomorphism solvers were certain incidence
structures of combinatorial objects (such as projective planes, Hadamard
matrices, Latin squares, etc.). Experiments show that starting from 1500
vertices our new instances are several orders of magnitude more difficult on
comparable input sizes. More importantly, our method is generic and efficient
in the sense that one can quickly create many isomorphism instances on a
desired number of vertices. In contrast to this, said combinatorial objects are
rare and difficult to generate and with the new construction it is possible to
generate an abundance of instances of arbitrary size. Our construction hinges
on the multipedes of Gurevich and Shelah and the Cai-F\"{u}rer-Immerman gadgets
that realize a certain abelian automorphism group and have repeatedly played a
role in the context of graph isomorphism. Exploring limits of such
constructions, we also explain that there are group theoretic obstructions to
generalizing the construction with non-abelian gadgets.Comment: 32 page
An Improved Isomorphism Test for Bounded-Tree-Width Graphs
We give a new fpt algorithm testing isomorphism of n-vertex graphs of tree width k in time 2^{k polylog(k)} poly n, improving the fpt algorithm due to Lokshtanov, Pilipczuk, Pilipczuk, and Saurabh (FOCS 2014), which runs in time 2^{O(k^5 log k)}poly n. Based on an improved version of the isomorphism-invariant graph decomposition technique introduced by Lokshtanov et al., we prove restrictions on the structure of the automorphism groups of graphs of tree width k. Our algorithm then makes heavy use of the group theoretic techniques introduced by Luks (JCSS 1982) in his isomorphism test for bounded degree graphs and Babai (STOC 2016) in his quasipolynomial isomorphism test. In fact, we even use Babai\u27s algorithm as a black box in one place. We give a second algorithm which, at the price of a slightly worse run time 2^{O(k^2 log k)}poly n, avoids the use of Babai\u27s algorithm and, more importantly, has the additional benefit that it can also be used as a canonization algorithm
L'ozone en Franche-Comté
Depuis près de 20 ans, l'ozone apparaît fréquemment à la une de nos quotidiens : " trou d'ozone " dans la stratosphère, trop d'ozone dans les basses couches de l'atmosphère... Ces problèmes méritent que l'on s'y intéresse car l'ozone est, à bien des titres, un composant important de la physico-chimie et de la qualité de l'air. Avant de nous pencher sur la situation en Franche-Comté, il nous est apparu souhaitable de présenter un court récapitulatif sur le sujet
Cuerpo, materia y ausencia
Body, matter and absence is a project that reflects about body and contemporary being, generating an unprecedented artwork through sculpture and drawing. Artistic research is based on the contributions of art, literary and philosophical references. The metaphorical body exploration generates a process of abstraction that’s possible by technical resCuerpo, materia y ausencia es un proyecto que reflexiona sobre el cuerpo y el ser contemporáneo generando obra plástica inĂ©dita que se vehicula a travĂ©s de la escultura y el dibujo. La investigaciĂłn plástica se acompaña y fundamenta a partir de las aportaciones de referentes artĂsticos, literarios y filosĂłficos. La exploraciĂłn metafĂłrica del cuerpoSchweitzer, D. (2014). Cuerpo, materia y ausencia. http://hdl.handle.net/10251/51097.Archivo delegad
Experimentelle und simulative Untersuchung der Wasserdampfvergasung von Klärschlamm und weiteren biogenen Brennstoffen
Die allotherme Zweibett-Wirbelschichtwasserdampfvergasung ist ein thermochemisches Konversionsverfahren zur Umwandlung eines festen Brennstoffes in ein wasserstoffreiches und hochqualitatives Produktgas. In dieser Arbeit wird mittels experimenteller und simulativer Methoden der Einfluss verschiedener kostengünstiger biogener Brennstoffe wie Klärschlamm, Rinder- und Schweinegülle sowie Holzpellets auf den Vergasungsprozess untersucht.
Die experimentellen Untersuchungen haben gezeigt, dass die Wasserdampfvergasung dieser biogenen Brennstoffe möglich ist: Die Untersuchungen zeigten, dass eine hohe Produktgasausbeute erreicht werden kann. Ebenso zeigte sich, dass sich die Zusammensetzung des Produktgases zwischen den verschiedenen Brennstoffen nur leicht unterscheidet. Zu berücksichtigen ist allerdings eine deutlich erhöhte Konzentration an Begleitgasen wie Teere, NH3, H2S oder HCl im Produktgas bei der Vergasung von biogenen Brennstoffen.
Basierend auf den experimentellen Ergebnissen wurde ein Prozessmodell der Wasserdampfvergasung von Klärschlamm erstellt. Mittels der Prozesssimulation konnten Kaltgaswirkungsgrade von nahezu 70 % berechnet werden
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