Buscador

Encontrado(s) 2108138 resultado(s)
Encontrada(s) 210814 página(s)

Gromov hiperbolicity in graphs

  • Carballosa Torres, Walter
If X is a geodesic metric space and x1, x2, x3 ∈ X, a geodesic triangle T = {x1, x2, x3} is the union of the three geodesics [x1x2], [x2x3] and [x3x1] in X. The space X is δ-hyperbolic (in the Gromov sense) if any side of T is contained in the δ-neighborhood of the union of the two other sides, for every geodesic triangle T in X. We denote by δ(X) the sharp hyperbolicity constant of X, i.e., δ(X) := inf{δ ≥ 0 : X is δ-hyperbolic } . The study of hyperbolic graphs is an interesting topic since the hyperbolicity of a geodesic metric space is equivalent to the hyperbolicity of a graph related to it. One of the main aims of this PhD Thesis is to obtain quantitative information about the distortion of the hyperbolicity constant of the graph G \ e obtained from the graph G by deleting an arbitrary edge e from it. These inequalities allow to obtain other main result, which characterizes in a quantitative way the hyperbolicity of any graph in terms of local hyperbolicity. In this work we also obtain information about the hyperbolicity constant of the line graph L(G) in terms of properties of the graph G. In particular, we prove qualitative results as the following: a graph G is hyperbolic if and only if L(G) is hyperbolic; if {Gn} is a T-decomposition of G ({Gn} are simple subgraphs of G), the line graph L(G) is hyperbolic if and only if supn δ(L(Gn)) is finite. Besides, we obtain quantitative results when k is the length of the edges of G and L(G). Two of them are quantitative versions of our qualitative results. We also prove that g(G)/4 ≤ δ(L(G)) ≤ c(G)/4 + 2k, where g(G) is the girth of G and c(G) is its circumference. We show that δ(L(G)) ≥ sup{L(g) : g is an isometric cycle in G}/4. Besides, we obtain bounds for δ(G) + δ(L(G)). Also, we characterize the graphs G with δ(L(G)) < k. Furthermore, we consider G with edges of arbitrary lengths, and L(G) with edges of non-constant lengths. In particular, we prove that a cycle of the graph G is transformed isometrically into a cycle of the graph L(G) with the same length. We also prove that δ(G) ≤ δ(L(G)) ≤ 5δ(G) + 3lmax, where lmax := supe∈E(G) L(e). This result implies the monotony of the hyperbolicity constant under a non-trivial transformation (the line graph of a graph). Also, we obtain criteria which allow us to decide, for a large class of graphs, whether they are hyperbolic or not. We are especially interested in the planar graphs which are the “boundary” (the 1-skeleton) of a tessellation of the Euclidean plane. Furthermore, we prove that a graph obtained as the 1-skeleton of a general CW 2-complex is hyperbolic if and only if its dual graph is hyperbolic. One of the main problems on this subject is to relate the hyperbolicity with other properties on graph theory. We extend in two ways (edge-chordality and path-chordality) the classical definition of chordal graphs in order to relate this property with Gromov hyperbolicity. In fact, we prove that every edge-chordal graph is hyperbolic and that every hyperbolic graph is path-chordal. Furthermore, we prove that every path-chordal cubic graph (with small path-chordality constant) is hyperbolic. Some previous works characterize the hyperbolic product graphs (for the Cartesian product, strong product and lexicographic product) in terms of properties of the factor graphs. Finally, we characterize the hyperbolic product graphs for two important kinds of products: the graph join G1 ⊎G2 and the corona G1 ⋄G2. The graph join G1 ⊎G2 is always hyperbolic, and G1 ⋄ G2 is hyperbolic if and only if G1 is hyperbolic. Furthermore, we obtain simple formulae for the hyperbolicity constant of the graph join G1 ⊎ G2 and the corona G1 ⋄ G2. ------------------------------------------------------------------------------, Sea X un espacio métrico geodésico y x1, x2, x3 ∈ X. Un triángulo geodésico T = {x1, x2, x3} es la unión de tres geodésicas [x1x2], [x2x3] y [x3x1] de X. El espacio X es δ- hiperbólico (en el sentido de Gromov) si todo lado de T está contenido en la δ-vecindad de la unión de los otros dos lados, para todo triángulo geodésico T de X. Se denota por δ(X) a la constante de hiperbolicidad óptima de X, es decir, δ(X) := inf{δ ≥ 0 : X es δ-hiperbólico }. El estudio de los grafos hiperbólicos es un tema interesante dado que la hiperbolicidad de un espacio métrico geodésico es equivalente a la hiperbolicidad de un grafo más sencillo asociado al espacio. Uno de los principales objetivos de esta Tesis Doctoral es obtener información cuantitativa sobre la variación de la constante de hiperbolicidad del grafo G \ e que se obtiene del grafo G mediante la eliminación de una arista arbitraria e de él. Estas desigualdades permiten caracterizar, de forma cuantitativa, la hiperbolicidad de cualquier grafo en términos de su hiperbolicidad local. En esta memoria se obtene información acerca de la constante de hiperbolicidad del grafo línea L(G) en términos de propiedades del grafo G. En particular, se obtienen los siguientes resultados cualitativos: un grafo G es hiperbólico si y sólo si L(G) es hiperbólico; si {Gn} es una T-descomposición de G, el grafo línea L(G) es hiperbólico si y sólo si supn δ(L(Gn)) es finito. Además, se obtienen resultados cuantitativos cuando las aristas de G y L(G) tienen longitud k. Se demuestra que g(G)/4 ≤ δ(L(G)) ≤ c(G)/4 + 2k, donde g(G) es el cuello de G y c(G) es su circunferencia. También se prueba que δ(L(G)) ≥ sup{L(g) : g es un ciclo isométrico de G}/4. Igualmente, se obtienen cotas para δ(G) + δ(L(G)) y se caracterizan los grafos G tales que δ(L(G)) < k. Por otra parte, se consideran grafos G con aristas de longitudes arbitrarias, y L(G) con aristas de longitudes no constante. En particular, se demuestra que los ciclos de G se transforman isométricamente en ciclos de L(G) con la misma longitud. También se obtiene la relación δ(G) ≤ δ(L(G)) ≤ 5δ(G) + 3lmax, donde lmax := supe∈E(G) L(e). Este resultado prueba la monotonía de la constante de hiperbolicidad bajo una transformación no trivial (el grafo línea de un grafo). También, se obtienen criterios que permiten decidir, para una clase amplia de grafos, cuando son estos hiperbólicos o no. Se presta especial atención en los grafos planares que son la “frontera” (el 1-esqueleto) de una teselación del plano euclídeo. Además, se prueba que los grafos que se obtienen como 1-esqueleto de un CW 2-complejo general son hiperbólicos si y sólo si su grafo dual es hiperbólico. Uno de los principales problemas en este área es relacionar la hiperbolicidad de un grafo con otras propiedades de la teoría de grafos. En este trabajo se extiende de dos maneras (arista-cordalidad y camino-cordalidad) la definición clásica de cordalidad con el fin de relacionar esta propiedad con la hiperbolicidad. De hecho, se demuestra que todo grafo arista-cordal es hiperbólico y que todo grafo hiperbólico es camino-cordal. También, se demuestra que todo grafo cúbico camino-cordal (con constante pequeña de camino-cordalidad) es hiperbólico. Algunos trabajos previos caracterizan la hiperbolicidad de productos de grafos (para el producto cartesiano, el producto fuerte y el producto lexicográfico) en términos de propiedades de los grafos factores. En el último capítulo, se caracteriza la hiperbolicidad de dos productos de grafos: el grafo join G1 ⊎ G2 y el corona G1 ⋄ G2. El grafo join G1 ⊎ G2 siempre es hiperbólico, y el corona G1 ⋄ G2 es hiperbólico si y sólo si G1 es hiperbólico. Además, obtenemos fórmulas sencillas para la constante de hiperbolicidad del grafo join G1 ⊎ G2 y del corona G1 ⋄ G2.
Proyecto:


La novela picaresca y Pirandello, The picaresque novel and Pirandello

  • Estévez Regidor, Francisco Aurelio
La noción de "literatura picaresca" se sitúa entra las más errantes y brumosas de la literatura comparada. El deseo de ampliar tan estricto coto ha redefinido el concepto en un sentido de "tradición picaresca", o incluso en los términos utilizados por Guillén o Blackburn, de un "mito picaresco". Visto entonces de modo dialéctico, y por vía del círculo hermenéutico, el género se enriquece y modifica continuamente con nuevas novelas. El difunto Matías Pascal, de Luigi Pirandello, exhibe elementos icónicos que remiten a la novela picaresca original y satisface los criterios mayores de dicha categoría crítica amplia. El protagonista de la novela, desde la poética del personaje picaresco y en clave evolutiva, después del intervalo romántico de héroes en su mayoría más homogéneos, redescubre el prototipo antitético de la novela crítica del seiscientos, de molde y ascendencia picaresca., The idea about picaresque novel got a place inside the most misty and wandering of the compared literature. With the purpose of expanding on that strict field, the concept has been redefine in a sense of "tradición picaresca", or even in terms used by Guillén or Blackburn, of a "mito picaresco". Then, in a dialectic way, and through the hermeutic circle, the genre is continuously enriched and modified with new novels. El difunto Matías Paseal, of Luigi Pirandello, shows iconic elements that refers to the original picaresque novel and satisfies the higher criteria of that enlarge critic category. The main character of the novel, from the poetic of the picaresque character and in a evolved key, after the romantic heroes interval mostly homogeneous, rediscover the opposite prototype of the 17th century critic novel, of origin and picaresque background., Publicado
Proyecto:


Recombining partitions via unimodality tests

  • Álvarez, Adolfo
  • Peña, Daniel
In this article we propose a recombination procedure for previously split data. It is basedon the study of modes in the density of the data, since departing from unimodality canbe a sign of the presence of clusters. We develop an algorithm that integrates a splitting process inherited from the SAR algorithm (Peña et al., 2004) with unimodality tests such as the dip test proposed by Hartigan and Hartigan (1985), and finally, we use anetwork configuration to visualize the results. We show that this can be a useful tool to detect heterogeneity in the data, but limited to univariate data because of the nature of the dip test. In a second stage we discuss the use of multivariate mode detection tests to avoid dimensionality reduction techniques such as projecting multivariate data into one dimension. The results of the application of multivariate unimodality tests show that is possible to detect the cluster structure of the data, although more research can be oriented to estimate the proper fine-tuning of some parameters of the test for a given dataset or distribution., Work partially supported by Spanish Ministry of Science and Innovation, research projects SEJ2007-64500 and ECO2012-38442
Proyecto:


Selecting and combining experts from survey forecasts

  • Fuentes, Julieta
  • Poncela, Pilar
  • Rodríguez, Julio
Combining multiple forecasts provides gains in prediction accuracy. Therefore, with the aim of finding an optimal weighting scheme, several combination techniques have been proposed in the forecasting literature. In this paper we propose the use of sparse partial least squares (SPLS) as a method to combine selected individual forecasts from economic surveys. SPLS chooses the forecasters with more predictive power about the target variable, discarding the panelists with redundant information. We employ the Survey of Professional Forecasters dataset to explore the performance of different methods for combining forecasts: average forecasts, trimmed mean, regression based methods and regularized methods also in regression. The results show that selecting and combining forecasts yields to improvements in forecasting accuracy compared to the hard to beat average of forecasters.
Proyecto:


Evaluación de la seguridad de sistemas embebidos ante ataques EMA

  • Martínez Bejarano, Roberto
Los sistemas embebidos de bajo consumo y alto rendimiento, cuya principal aplicación son los dispositivos portátiles tales como: teléfonos móviles, tabletas, consolas de juego, reproductores de música, lectores de libros etc. han experimentado un tremendo auge en los últimos años. Estos dispositivos, además de contener información confidencial (contraseñas, fotos, números de teléfono…) permiten, en su gran mayoría, realizar operaciones bajo redes inalámbricas poco seguras: como transacciones, envío de datos, acceso a cuentas personales etc. Por tanto, se hace imprescindible el análisis del nivel de seguridad alcanzado por estos dispositivos. Sin embargo, a la espera de futuros desarrollos de la estadística, todavía no existe un marco de evaluación de la seguridad totalmente satisfactorio e internacionalmente reconocido. Así por primera vez en este trabajo se evalúa la seguridad relativa de varios microprocesadores representativos del mercado de aplicaciones embebidas de bajo consumo, comparando su respuesta ante un ataque por canal lateral electromagnético. Los dispositivos seleccionados para su evaluación son:  8051 con arquitectura de 8 bits evolucionada (C8051F303 de Silicon Labs).  ARM7TDMI-S de 32 bits (LPC2124 de NXP).  Dos ARMCortexM3 de 32 bits nunca antes analizados ante ataques por canal lateral: con diseño de alto rendimiento (LPC1769 de NXP) y bajo consumo (STM32L152 de STMicroelectronics). Para la realización de los experimentos se desarrolla un setup propio de medida, altamente automatizado, robusto ante vibraciones y con una capacidad de muestreo superior a lo publicado hasta ahora en la bibliografía. También se propone una nueva métrica para comparar la respuesta de los dispositivos ante ataques por canal lateral, y que se apoya en la correlación estadística. Uno de los elementos cruciales en un ataque por canal lateral electromagnético es el dispositivo o sonda de medida. Las publicaciones de autores que sugieren la utilización de algún tipo de sonda, no aportan datos concluyentes. Este trabajo compara de forma novedosa la respuesta de tres tipos de sondas: dos fabricadas y comercializadas por Electrometrics EM6995 y Langer MFA-R y una tercera fabricada ad-hoc, y manualmente. Como resultado se concluye que cualquier tipo de sonda es factible de ser usada en un ataque electromagnético, aunque son mejores aquellas de alta precisión como la MFA-R de cabeza milimétrica y preamplificador integrado, que sin embargo requieren una preparación y un setup más elaborado. Como resultado final del estudio, se concluye que los dispositivos actuales ARM Cortex M3, ofrecen una seguridad inherente muy superior a la de otros microprocesadores de diseño menos elaborado, y en consecuencia es recomendable usarlos para aquellas aplicaciones cuyos requisitos de seguridad sean elevados. -------------, The low power and high performance embedded systems used in mobile devices like mobile phones, tablet computers, music readers, handheld game consoles, book readers… have achieved a great success in the last years. These devices contain confidence information (keys, photographs, telephone numbers…) and usually let us doing operations over unsafe wireless networks: banking transactions, sending data, accessing to personal accounts etc. In consequence, the analysis of the security level reached by these devices is indispensable. However, there isn’t a satisfactory and internationally recognized methodology to assess security. For first time, this work assesses the relative security of several representative low power embedded microprocessors, comparing their response against Electromagnetic Side Channel Attack. The selected devices for this evaluation are:  8051 with new 8 bits architecture (Silicon Labs C8051F303).  ARM7TDMI-S of 32 bits (NXP LPC2124).  Two 32 bits ARMCortexM3 never before analysed against Side Channel Attacks: with high performance (NXP LPC1769) and low power specifications (STMicroelectronics STM32L152). A measurement setup has been developed to carry out this study. It’s highly automatized, robustly against vibrations and with a higher sampling rate than rest of setups showed in bibliography. Also, a new metric is proposed. It allows to compare device response against correlation side channel attack using statistical correlation. One of the essential elements of an electromagnetic side channel attack is the near field probe. The authors, whose studies suggest the use of some type of probe, do not include conclusion results. This work compares the response of three probes in a new way: Electrometrics EM6995, Langer MFA-R and ones handmade. It concludes that any type of probe is useful in an electromagnetic attack, although the use of high precision probes is recommended. For example, the MFA-R with tiny head and integrated preamplifier. Nevertheless, it requires more training and a precise setup. This study finds out that the updated devices ARM Cortex M3, have a very high security, higher than traditional ones. Therefore, the use of this type of devices in sensitive applications is advisable.
Proyecto:


Los mecanismos nacionales de prevención de la tortura previstos por el protocolo facultativo a la Convención de Naciones Unidas contra la tortura y otros tratos o penas crueles, inhumanos o degradantes : el mecanismo nacional de prevención de la tortura en España

  • Pino Gamero, Esther
Máster Oficial en Estudios Avanzados en Derechos Humanos, Presidente: Francisco Javier Ansuátegui; Vocal: Emilio Pajares; Secretario: Ignacio Campoy Cervera
Proyecto:


A Cloud-Based Architecture for an Affective Recommender System of Learning Resources

  • Leony, Derick
  • Pardo Sánchez, Abelardo
  • Parada Gélvez, Hugo A.
  • Delgado Kloos, Carlos
Proceedings of: 1st International Workshop on Cloud Education Environments (WCLOUD 2012), Antigua, Guatemala, November 15-16, 2012., One of the most common functionalities in cloudbased learning environments is the recommendation of learning resources. Many approaches have been proposed to deploy recommender systems into an educational environment. Currently, there is an increasing interest in including affective information into the process to generate the recommendations for the learner. In this paper, we propose a cloud-based architecture for a system that recommends learning resources according to the affective state of the learner. Furthermore, we provide the details of an implementation of the architecture along with a discussion on the advantages and disadvantages of the proposal., Work partially funded by the EEE project, “Plan Nacional de I+D+I TIN2011-28308-C03-01”, the “Emadrid: Investigación y desarrollo de tecnologías para el e-learning en la Comunidad de Madrid” project (S2009/TIC-1650), and “Consejo Social - Universidad Carlos III de Madrid”., Publicado
Proyecto:


Architecture for Collaborative Learning Activities in Hybrid Learning Environments

  • Ibáñez, María Blanca
  • Maroto, David
  • García Rueda, José Jesús
  • Leony, Derick
  • Delgado Kloos, Carlos
3D virtual worlds are recognized as collaborative learning environments. However, the underlying technology is not sufficiently mature and the virtual worlds look cartoonish, unlinked to reality. Thus, it is important to enrich them with elements from the real world to enhance student engagement in learning activities. Our approach is to build learning environments where participants can either be in the real world or in its mirror world while sharing the same hybrid space in a collaborative learning experience. This paper focuses on the system architecture and a usability study of a proof-of-concept for these hybrid learning environments. The architecture allows the integration of the real world and its 3D virtual mirror; the exchange and geolocalization of multimodal information, and also the orchestration of learning activities. The results of the usability evaluation show positive engagement effects on participants in the mirror world and, to a lesser extent, on those in the real world., This research has been partially supported by the following projects: “España Virtual” within the Ingenio 2010 program, subcontracted by Elecnor Deimos, "EEE" (TIN2011-28308-C03-01) funded by the Spanish National Plan of Research, Development and Innovation, and "eMadrid", S2009/TIC-1650 “Investigación y Desarrollo de tecnologías para el e-learning en la Comunidad de Madrid” funded by the Region of Madrid., Publicado
Proyecto:


Maggie: A Social Robot as a Gaming Platform

  • González Pacheco, Víctor
  • Ramey, Arnaud
  • Alonso Martín, Fernando
  • Castro González, Álvaro
  • Salichs Sánchez-Caballero, Miguel
Edutainment robots are robots designed to participate in people's education and in their entertainment. One of the tasks of edutainment robots is to play with their human partners, but most of them offer a limited pool of games. Moreover, it is difficult to add new games to them. This lack of flexibility could shorten their life cycle. This paper presents a social robot on which several robotic games have been developed. Our robot uses a flexible and modular architecture that allows the creation of new skills by the composition of existing and simpler skills. With this architecture, the development of a new game mainly consists in the composition of the skills that are needed for this specific game. In this paper, we present the robot, its hardware and its software architecture, including its interaction capabilities. We also provide a detailed description of the development of five of the games the robot can play., The authors gratefully acknowledge the funds provided by the Spanish MICINN (Ministry of Science and Innovation) through the project "A new Approach to Social Robotics (AROS)". The research leading to these results has also received funding from the RoboCity2030-II-CM project(S2009/DPI-1559), funded by Programas de Actividades I+D en la Comunidad de Madrid and cofunded by Structural Funds ofthe EU.
Proyecto:


A Distributed Collaborative System for Flexible Learning Content Production and Management

  • Pardo Sánchez, Abelardo
  • Arias Fisteus, Jesús
  • Delgado Kloos, Carlos
Authoring learning content is an area under pressure due to conflicting requirements. Adaptive, templatebased, highly interactive, multimedia-rich content is desired for current learning environments. At the same time, authors need a system supporting collaboration, easy re-purposing, and continuous updates with a lower adoption barrier to keep the production process simple, specially for high enrollment learning scenarios. Other areas such as software development have adopted effective methodologies to cope with a similar increase in complexity. In this paper an authoring system is presented to support a community of authors in the creation of learning content. A set of pre-defined production rules and templates are offered. Following the single source approach, authors create documents that are then automatically processed to obtain various derived resources. The toolkit allows for simple continuous updates, the re-use and re-purpose of course material, as well as the adaptation of resources to different target groups and scenarios. The toolkit has been validated by analyzing its use over a three year period in two high enrollment engineering courses. The results show effective support and simplification of the production process as well as its sustainability over time., Work partially funded by the EEE project, “Plan Nacional de I+D+I TIN2011-28308-C03-01”, and the “Emadrid: Investigación y desarrollo de tecnologías para el e-learning en la Comunidad de Madrid” project (S2009/TIC-1650)., Publicado
Proyecto:


Buscador avanzado