Special asteroidal quadruple on directed path graph non rooted path graph

An asteroidal triple in a graph G is a set of three non- adjacent vertices such that for any two of them there exists a path be- tween them that does not intersect the neighborhood of the third. Special asteroidal triple in a graph G is an asteroidal triple such that each pair is linked by a special connection. A special asteroidal triples play a central role in a characterization of directed path graphs by Cameron, Hoáng and Lévêque. They also introduce a related notion of asteroidal quadru- ple and conjecture a characterization of rooted path graphs. In its original form this conjecture is not complete, still in leafage four, as was showed in. But, as suggested by the conjecture, a characterization by forbidding particular types of asteroidal quadruples may hold. We prove that the conjecture in the original form is true on directed path graphs with leafage four having two minimal separators with multiplicity two. Thus we build the family of forbidden subgraphs in this case.Sociedad Argentina de Informática e Investigación Operativ

Special asteroidal quadruple on directed path graph non rooted path graph

An asteroidal triple in a graph G is a set of three non- adjacent vertices such that for any two of them there exists a path be- tween them that does not intersect the neighborhood of the third. Special asteroidal triple in a graph G is an asteroidal triple such that each pair is linked by a special connection. A special asteroidal triples play a central role in a characterization of directed path graphs by Cameron, Hoáng and Lévêque. They also introduce a related notion of asteroidal quadru- ple and conjecture a characterization of rooted path graphs. In its original form this conjecture is not complete, still in leafage four, as was showed in. But, as suggested by the conjecture, a characterization by forbidding particular types of asteroidal quadruples may hold. We prove that the conjecture in the original form is true on directed path graphs with leafage four having two minimal separators with multiplicity two. Thus we build the family of forbidden subgraphs in this case.Sociedad Argentina de Informática e Investigación Operativ

Extended star graphs

Chordal graphs, which are intersection graph of subtrees of a tree, can be represented on trees. Some representation of a chordal graph often reduces the size of the data structure needed to store the graph, permitting the use of extremely efficient algorithms that take advantage of the compactness of the representation. An extended star graph is the intersection graph of a family of subtrees of a tree that has exactly one vertex of degree at least three. An asteroidal triple in a graph is a set of three non-adjacent vertices such that for any two of them there exists a path between them that does not intersect the neighborhood of the third. Several subclasses of chordal graphs (interval graphs, directed path graphs) have been characterized by forbidden asteroids. In this paper, we define, a subclass of chordal graphs, called extended star graphs, prove a characterization of this class by forbidden asteroids and show open problems

Risposta dinamica strutturale di superyacht: aspetti normativi e verifiche preliminari

Il livello di comfort a bordo dei moderni superyacht \ue8 stato recentemente oggetto di attenzione da parte delle pi\uf9 importanti Societ\ue0 di Classifica che hanno emanato nuove direttive per la valutazione delle vibrazioni e del rumore. Tali direttive, indicate genericamente come "Comfort Class Rules" contengono sia i criteri per la misura delle vibrazioni e del rumore in diverse zone dello scafo, sia i valori massimi entro i quali tali misure devono rientrare affinch\ue8 all'unit\ue0 possa venire assegnata la "Comfort Class". Per quanto riguarda pi\uf9 specificamente le vibrazioni, oggetto del presente studio, tutte le normative sono ispirate alle gi\ue0 esistenti regolamentazioni ISO del 1984, sostituite recentemente dalle norme ISO 2000. Nonostante lo sforzo da parte delle Societ\ue0 di Classifica di mantenere una certa omogeneit\ue0 nei criteri e nei valori massimi ammessi, molte normative presentano ancora differenze che possono mettere in difficolt\ue0 gli operatori. In questo lavoro viene presentata una sintesi delle principali regolamentazioni attualmente esistenti in merito alla Comfort Class per unit\ue0 da diporto. Vengono poi descritte le fasi principali di una indagine numerica condotta su un superyacht di 55 metri di lunghezza avente lo scopo di studiare il comportamento dinamico della parte poppiera dello scafo in acciaio e delle sovrastrutture in alluminio per evidenziarne eventuali criticit\ue0 e confrontare i risultati con i limiti proposti dalle normative. L'indagine prevede anche una conferma sperimentale che sar\ue0 condotta prossimamente in cantiere