897 research outputs found
Universality in percolation of arbitrary Uncorrelated Nested Subgraphs
The study of percolation in so-called {\em nested subgraphs} implies a
generalization of the concept of percolation since the results are not linked
to specific graph process. Here the behavior of such graphs at criticallity is
studied for the case where the nesting operation is performed in an
uncorrelated way. Specifically, I provide an analyitic derivation for the
percolation inequality showing that the cluster size distribution under a
generalized process of uncorrelated nesting at criticality follows a power law
with universal exponent . The relevance of the result comes from
the wide variety of processes responsible for the emergence of the giant
component that fall within the category of nesting operations, whose outcome is
a family of nested subgraphs.Comment: 5 pages, no figures. Mistakes found in early manuscript have been
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Evolución durante el Cuaternario del Barranco de Tirajana, Gran Canaria
[Resumen] El barranco de Tirajana en su evolución ha pasado por diferentes etapas. Se ha podido constatar que ya funcionaba en el Mioceno superior pero su evolución principal se ha desarrollado en el Cuaternario entre los 0.6 m.a. y los 125.000 años. En este periodo se produce la depresión de Tirajana, que es la cuenca superior actual, como resultado de la producción de grandes deslizamientos de terreno (Lomoschitz y Corominas, 1992a y b; YLomoschitz, 1995). Asimismo, se ha comprobado que el desalojo hacia el mar de los materiales deslizados es lo que justifica la formación del complejo deltaico de Juan Grande,
que es el único depósito de estas características de la isla.[Abstract] The evolution of the Barranco de Tirajana has followed different stages. We conclude that it was already active in upper Miocene although the main development ocurred in the Quaternary, 0.6 m.y. to 125.000 years ago. In this period Tirajana's Depression was originated, which is nowadays the upper basin, due to the triggering of large landslides in the area (Lomoschitz & Corominas, 1992a and b; Lomoschitz, 1995). Due the mobilization of the slide material to the sea it has built a complex deltaic formation named Juan Grande, unique in Gran Canaria
Switcher-random-walks: a cognitive-inspired mechanism for network exploration
Semantic memory is the subsystem of human memory that stores knowledge of
concepts or meanings, as opposed to life specific experiences. The organization
of concepts within semantic memory can be understood as a semantic network,
where the concepts (nodes) are associated (linked) to others depending on
perceptions, similarities, etc. Lexical access is the complementary part of
this system and allows the retrieval of such organized knowledge. While
conceptual information is stored under certain underlying organization (and
thus gives rise to a specific topology), it is crucial to have an accurate
access to any of the information units, e.g. the concepts, for efficiently
retrieving semantic information for real-time needings. An example of an
information retrieval process occurs in verbal fluency tasks, and it is known
to involve two different mechanisms: -clustering-, or generating words within a
subcategory, and, when a subcategory is exhausted, -switching- to a new
subcategory. We extended this approach to random-walking on a network
(clustering) in combination to jumping (switching) to any node with certain
probability and derived its analytical expression based on Markov chains.
Results show that this dual mechanism contributes to optimize the exploration
of different network models in terms of the mean first passage time.
Additionally, this cognitive inspired dual mechanism opens a new framework to
better understand and evaluate exploration, propagation and transport phenomena
in other complex systems where switching-like phenomena are feasible.Comment: 9 pages, 3 figures. Accepted in "International Journal of
Bifurcations and Chaos": Special issue on "Modelling and Computation on
Complex Networks
Computational modelling of hydrogen assisted fracture in polycrystalline materials
We present a combined phase field and cohesive zone formulation for hydrogen
embrittlement that resolves the polycrystalline microstructure of metals.
Unlike previous studies, our deformation-diffusion-fracture modelling framework
accounts for hydrogen-microstructure interactions and explicitly captures the
interplay between bulk (transgranular) fracture and intergranular fracture,
with the latter being facilitated by hydrogen through mechanisms such as grain
boundary decohesion. We demonstrate the potential of the theoretical and
computational formulation presented by simulating inter- and trans-granular
cracking in relevant case studies. Firstly, verification calculations are
conducted to show how the framework predicts the expected qualitative trends.
Secondly, the model is used to simulate recent experiments on pure Ni and a
Ni-Cu superalloy that have attracted particular interest. We show that the
model is able to provide a good quantitative agreement with testing data and
yields a mechanistic rationale for the experimental observations
Matching structure and bargaining outcomes in buyer–seller networks
We examine the relationship between the matching structure of a bipartite (buyer-seller) network and the (expected) shares of the unit surplus that each connected pair in this network can create. We show that in different bargaining environments, these shares are closely related to the Gallai-Edmonds Structure Theorem. This theorem characterizes the structure of maximum matchings in an undirected graph. We show that the relationship between the (expected) shares and the tructure Theorem is not an artefact of a particular bargaining mechanism or trade centralization. However, this relationship does not necessarily generalize to non-bipartite networks or to networks with heterogeneous link values
Robustness of the European power grids under intentional attack
The power grid defines one of the most important technological networks of
our times and sustains our complex society. It has evolved for more than a
century into an extremely huge and seemingly robust and well understood system.
But it becomes extremely fragile as well, when unexpected, usually minimal,
failures turn into unknown dynamical behaviours leading, for example, to sudden
and massive blackouts. Here we explore the fragility of the European power grid
under the effect of selective node removal. A mean field analysis of fragility
against attacks is presented together with the observed patterns. Deviations
from the theoretical conditions for network percolation (and fragmentation)
under attacks are analysed and correlated with non topological reliability
measures.Comment: 7 pages, 4 figure
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