DSpace Community:
http://hdl.handle.net/2117/3178
20141023T03:15:43Z

Quantum Google in a complex network
http://hdl.handle.net/2117/24220
Title: Quantum Google in a complex network
Authors: Paparo, Giuseppe Davide; Muller, Markus; Comellas Padró, Francesc de Paula; Martin Delgado, Miguel Angel
Abstract: We investigate the behaviour of the recently proposed Quantum PageRank algorithm, in large complex networks. We find that the algorithm is able to univocally reveal the underlying topology of the network and to identify and order the most relevant nodes. Furthermore, it is capable to clearly highlight the structure of secondary hubs and to resolve the degeneracy in importance of the low lying part of the list of rankings. The quantum algorithm displays an increased stability with respect to a variation of the damping parameter, present in the Google algorithm, and a more clearly pronounced powerlaw behaviour in the distribution of importance, as compared to the classical algorithm. We test the performance and confirm the listed features by applying it to real world examples from the WWW. Finally, we raise and partially address whether the increased sensitivity of the quantum algorithm persists under coordinated attacks in scalefree and random networks.
20141002T17:35:16Z

On the representability of the biuniform matroid
http://hdl.handle.net/2117/24101
Title: On the representability of the biuniform matroid
Authors: Ball, Simeon Michael; Padró Laimon, Carles; Weiner, Zsuzsa; Xing, Chaoping
Abstract: Every biuniform matroid is representable over all sufficiently large fields. But it is not known exactly over which finite fields they are representable, and the existence of efficient methods to find a representation for every given biuniform matroid has not been proved. The interest of these problems is due to their implications to secret sharing. The existence of efficient methods to find representations for all biuniform matroids is proved here for the first time. The previously known efficient constructions apply only to a particular class of biuniform matroids, while the known general constructions were not proved to be efficient. In addition, our constructions provide in many cases representations over smaller finite fields.
© 2013, Society for Industrial and Applied Mathematics
20140918T16:05:12Z

The degreediameter problem in maximal bipartite planar graphs
http://hdl.handle.net/2117/24097
Title: The degreediameter problem in maximal bipartite planar graphs
Authors: Dalfó Simó, Cristina; Huemer, Clemens; Salas, Julian
Abstract: The (A ,D) (degree/diameter) problem consists of finding the largest possible number of vertices n among all the graphs with maximum degree and diameter D. We consider the (A ,D) problem for maximal planar bipartite graphs, that are simple planar graphs in which every face is a quadrangle. We obtain that for the ( , 2) problem, the number of vertices is n = + 2; and for the ( , 3) problem, n = 3 1 if is odd and n = 3 2 if is even. Then, we study the general case ( A ,D) and obtain that an upper bound on n is approximately 3(2D+1)( 2)bD/2c,
and another one is C(  2)bD/2c if D and C is a sufficiently large constant.
Our upper bounds improve for our kind of graphs the one given by Fellows, Hell and Seyffarth for general planar graphs. We also give a lower bound on n for maximal planar bipartite graphs, which is approximately (  2)k if D = 2k, and 3(  3)k if D = 2k + 1, for and D sufficiently large in both cases.
20140918T10:55:22Z

A bound for the maximum weight of a linear code
http://hdl.handle.net/2117/24092
Title: A bound for the maximum weight of a linear code
Authors: Ball, Simeon Michael; Blokhuis, Aart
Abstract: It is shown that the parameters of a linear code over Fq of length n, dimension k, minimum weight d, and maximum weight m satisfy a certain congruence relation. In the case that q = p is a prime, this leads to the bound m &le (nd)pe(p1), where e {0, 1,.., k2} is maximal with the property that (nde) 0 (mod pk1e). Thus, if C contains a codeword of weight n, then nd/(p1)+d+e. The results obtained for linear codes are translated into corresponding results for (n, t)arcs and tfold blocking sets of AG(k1, q). The bounds obtained in these spaces are better than the known bounds for these geometrical objects for many parameters
20140917T17:03:50Z

Simulation of cable dynamics for moored ocean platforms: modeling aids design of large, underwater power cable
http://hdl.handle.net/2117/23616
Title: Simulation of cable dynamics for moored ocean platforms: modeling aids design of large, underwater power cable
Authors: Prat Farran, Joana d'Arc; Zaragoza Monroig, M. Luisa; Río Fernandez, Joaquín del
20140725T10:56:15Z

Perfect edgemagic graphs
http://hdl.handle.net/2117/22939
Title: Perfect edgemagic graphs
Authors: López Masip, Susana Clara; Muntaner Batle, Francesc Antoni; Rius Font, Miquel
Abstract: The study of the possible valences for edgemagic labelings of graphs has motivated us to introduce the concept of perfect edgemagic graphs. Intuitively speaking, an edgemagic graph is perfect edgemagic if all possible theoretical valences occur. In particular, we prove that for each integer m > 0, that is the power of an odd prime, and for each natural number n, the crown product Cm circle dot (Kn) over bar is perfect edgemagic. Related results are also provided concerning other families of unicyclic graphs. Furthermore, several open questions that suggest interesting lines for future research are also proposed.
20140509T09:45:58Z

The (Delta,D) and (Delta,N) problems in doublestep digraphs with unilateral distance
http://hdl.handle.net/2117/22938
Title: The (Delta,D) and (Delta,N) problems in doublestep digraphs with unilateral distance
Authors: Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel
Abstract: We study the (delta;D) and (delta;N) problems for doublestep digraphs considering the unilateral distance, which is the minimum between the distance in the digraph and the distance in its converse digraph, the latter obtained by changing the directions of all the arcs. The first problem consists of maximizing the number of vertices N of a digraph, given the
maximum degree and the unilateral diameter D , whereas the second one (somehow dual of the first) consists of minimizing the unilateral diameter given the maximum degree and the number of vertices. We solve the first problem for every value of the unilateral diameter and the second one
for infinitely many values of the number of vertices. Moreover, we compute the mean unilateral distance of the digraphs in the families considered.
20140509T09:30:19Z

Corrigendum to "Algebraic characterizations of regularity properties in bipartite graphs" Eur. J. Combin. 34 (2013) 12231231
http://hdl.handle.net/2117/22446
Title: Corrigendum to "Algebraic characterizations of regularity properties in bipartite graphs" Eur. J. Combin. 34 (2013) 12231231
Authors: Abiad, Aida; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel
Description: Corrigendum d'un article anteriorment publicat
20140331T10:03:52Z

The (Delta,D) and (Delta,N) problems in doublestep digraphs with unilateral diameter
http://hdl.handle.net/2117/22316
Title: The (Delta,D) and (Delta,N) problems in doublestep digraphs with unilateral diameter
Authors: Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel
Abstract: We study the (D;D) and (D;N) problems for doublestep digraphs considering
the unilateral distance, which is the minimum between the distance in the digraph
and the distance in its converse digraph, obtained by changing the directions
of all the arcs.
The first problem consists of maximizing the number of vertices N of a digraph,
given the maximum degree D and the unilateral diameter D , whereas the
second one consists of minimizing the unilateral diameter given the maximum
degree and the number of vertices. We solve the first problem for every value
of the unilateral diameter and the second one for some infinitely many values of
the number of vertices.
Miller and Sirán [4] wrote a comprehensive survey about (D;D) and (D;N)
problems. In particular, for the doublestep graphs considering the standard
diameter, the first problem was solved by Fiol, Yebra, Alegre and Valero [3],
whereas Bermond, Iliades and Peyrat [2], and also Beivide, Herrada, Balcázar
and Arruabarrena [1] solved the (D;N) problem. In the case of the doublestep
digraphs, also with the standard diameter, Morillo, Fiol and Fàbrega [5] solved
the (D;D) problem and provided some infinite families of digraphs which solve
the (D;N) problem for their corresponding numbers of vertices
20140320T13:31:57Z

Algebraic Characterizations of Regularity Properties in Bipartite Graphs
http://hdl.handle.net/2117/22312
Title: Algebraic Characterizations of Regularity Properties in Bipartite Graphs
Authors: Abiad Monge, Aida; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel
Abstract: Regular and distanceregular characterizations of general graphs are wellknown. In particular, the spectral excess theorem states that a connected graph GG is distanceregular if and only if its spectral excess (a number that can be computed from the spectrum) equals the average excess (the mean of the numbers of vertices at extremal distance from every vertex). The aim of this paper is to derive new characterizations of regularity and distanceregularity for the more restricted family of bipartite graphs. In this case, some characterizations of (bi)regular bipartite graphs are given in terms of the mean degrees in every partite set and the Hoffman polynomial. Moreover, it is shown that the conditions for having distanceregularity in such graphs can be relaxed when compared with general graphs. Finally, a new version of the spectral excess theorem for bipartite graphs is presented.
20140320T12:40:12Z

Edgedistanceregular graphs are distanceregular
http://hdl.handle.net/2117/22307
Title: Edgedistanceregular graphs are distanceregular
Authors: Cámara Vallejo, Marc; Dalfó Simó, Cristina; Delorme, Charles; Fiol Mora, Miquel Àngel; Suzuki, Hiroshi
Abstract: A graph is edgedistanceregular when it is distanceregular around each of its edges and it has the same intersection numbers for any edge taken as a root. In this paper we give some (combinatorial and algebraic) proofs of the fact that every edgedistanceregular graph Γ is distanceregular and homogeneous. More precisely, Γ is edgedistanceregular if and only if it is bipartite distanceregular or a generalized odd graph. Also, we obtain the relationships between some of their corresponding parameters, mainly, the distance polynomials and the intersection numbers.
20140320T10:40:00Z

Energy and carbon emissions aware services allocation with delay for Data Centers
http://hdl.handle.net/2117/22066
Title: Energy and carbon emissions aware services allocation with delay for Data Centers
Authors: Guillén, Bernat; Hesselbach Serra, Xavier; Muñoz López, Francisco Javier; Klingert, Sonja
Abstract: This paper presents a new approach to service
assignment in Data Centers (DC), relating it to a classical
combinatory problem called Bin Packing Problem and adding
the possibility of delay and collaboration with users and energy
providers. This possibility proves to reduce in much the energy
consumption of the DC as well as the CO2 emissions.
20140314T13:05:00Z

Connectivity: properties and structure
http://hdl.handle.net/2117/22004
Title: Connectivity: properties and structure
Authors: Balbuena Martínez, Maria Camino Teófila; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel
Abstract: Connectivity is one of the central concepts of graph theory, from both a theoret ical and a practical point of view. Its theoretical implications are mainly based on the existence of nice maxmin characterization results, such as Menger’s theorems. In these theorems, one condition which is clearly necessary also turns out to be sufficient. Moreover, these results are closely related to some other key theorems in graph theory: Ford and Fulkerson’s theorem about flows and Hall’s theorem on perfect matchings. With respect to the applications, the study of connectivity parameters of graphs and digraphs is of great interest in the design of reliable and faulttolerant interconnection or communication networks.
Since graph connectivity has been so widely studied, we limit ourselves here to the presentation of some of the key results dealing with finite simple graphs and digraphs. For results about infinite graphs and connectivity algorithms the reader can consult, for instance, Aharoni and Diestel [AhDi94], Gibbons [Gi85], Halin [Ha00], Henzinger, Rao, and Gabow [HeRaGa00], Wigderson [Wi92]. For further details, we refer the reader to some of the good textbooks and surveys available on the subject: Berge [Be76], Bermond, Homobono, and Peyrat [BeHoPe89], Frank [Fr90, Fr94, Fr95], Gross and Yellen [GrYe06], Hellwig and Volkmann [HeVo08], Lov ´asz [Lo93], Mader [Ma79], Oellermann [Oe96], Tutte [Tu66].
20140312T12:00:55Z

Further topics in connectivity
http://hdl.handle.net/2117/22000
Title: Further topics in connectivity
Authors: Balbuena Martínez, Maria Camino Teófila; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel
Abstract: Continuing the study of connectivity, initiated in §4.1 of the Handbook, we survey here some (sufficient) conditions under which a graph or digraph has a given connectivity or edgeconnectivity. First, we describe results concerning maximal (vertex or edge) connectivity. Next, we deal with conditions for having (usually lower) bounds for the connectivity parameters. Finally, some other general connectivity measures, such as one instance of the socalled “conditional connectivity,” are considered.
For unexplained terminology concerning connectivity, see §4.1.
20140312T11:17:54Z

From clutters to matroids
http://hdl.handle.net/2117/21963
Title: From clutters to matroids
Authors: Fàbrega Canudas, José; Martí Farré, Jaume; Muñoz López, Francisco Javier
Abstract: This paper deals with the question of completing a monotone increasing family of subsets to obtain the dependent sets of a matroid. More precisely, we provide several natural ways of transforming the clutter of the inclusion minimal subsets of the family into the set of circuits of a matroid.
20140310T12:57:39Z