3,242 research outputs found
Synchronization of networks with variable local properties
We study the synchronization transition of Kuramoto oscillators in scale-free
networks that are characterized by tunable local properties. Specifically, we
perform a detailed finite size scaling analysis and inspect how the critical
properties of the dynamics change when the clustering coefficient and the
average shortest path length are varied. The results show that the onset of
synchronization does depend on these properties, though the dependence is
smooth. On the contrary, the appearance of complete synchronization is
radically affected by the structure of the networks. Our study highlights the
need of exploring the whole phase diagram and not only the stability of the
fully synchronized state, where most studies have been done up to now.Comment: 5 pages and 3 figures. APS style. Paper to be published in IJBC
(special issue on Complex Networks' Structure and Dynamics
Explosive Synchronization Transitions in Scale-free Networks
The emergence of explosive collective phenomena has recently attracted much
attention due to the discovery of an explosive percolation transition in
complex networks. In this Letter, we demonstrate how an explosive transition
shows up in the synchronization of complex heterogeneous networks by
incorporating a microscopic correlation between the structural and the
dynamical properties of the system. The characteristics of this explosive
transition are analytically studied in a star graph reproducing the results
obtained in synthetic scale-free networks. Our findings represent the first
abrupt synchronization transition in complex networks thus providing a deeper
understanding of the microscopic roots of explosive critical phenomena.Comment: 6 pages and 5 figures. To appear in Physical Review Letter
Dynamical Organization of Cooperation in Complex Topologies
In this Letter, we study how cooperation is organized in complex topologies
by analyzing the evolutionary (replicator) dynamics of the Prisoner's Dilemma,
a two-players game with two available strategies, defection and cooperation,
whose payoff matrix favors defection. We show that, asymptotically, the
population is partitioned into three subsets: individuals that always cooperate
({\em pure cooperators}), always defect ({\em pure defectors}) and those that
intermittently change their strategy. In fact the size of the latter set is the
biggest for a wide range of the "stimulus to defect" parameter. While in
homogeneous random graphs pure cooperators are grouped into several clusters,
in heterogeneous scale-free (SF) networks they always form a single cluster
containing the most connected individuals (hubs). Our results give further
insights into why cooperation in SF networks is favored.Comment: 4 pages and 4 figures. Final version as published in Physical Review
Letter
Base de Datos de Investigación en Agricultura para el Desarrollo: Resultados preliminares
Comunicación presentada en el I Congreso Investigación en Agricultura para el Desarrollo, celebrado en Madrid el 17 y 18 de octubre de 2011.La investigación en agricultura para el desarrollo en España carece de un organismo o una estructura que coordine la información y la producción científica. El único informe previo donde se analizó la actividad en este ámbito fue el "Informe sobre la Cooperación Universitaria al Desarrollo en al Ámbito Agroalimentario - El caso español", realizado por las fundaciones Triptolemos y Cultura de Paz, correspondiente al año 2006-2007.Este trabajo está financiado por el proyecto AECID CAP10-0080 y la ayuda INIA AC2010-00037.Peer Reviewe
Paths to Synchronization on Complex Networks
The understanding of emergent collective phenomena in natural and social
systems has driven the interest of scientists from different disciplines during
decades. Among these phenomena, the synchronization of a set of interacting
individuals or units has been intensively studied because of its ubiquity in
the natural world. In this paper, we show how for fixed coupling strengths
local patterns of synchronization emerge differently in homogeneous and
heterogeneous complex networks, driving the process towards a certain global
synchronization degree following different paths. The dependence of the
dynamics on the coupling strength and on the topology is unveiled. This study
provides a new perspective and tools to understand this emerging phenomena.Comment: Final version published in Physical Review Letter
Synchronization in Random Geometric Graphs
In this paper we study the synchronization properties of random geometric
graphs. We show that the onset of synchronization takes place roughly at the
same value of the order parameter that a random graph with the same size and
average connectivity. However, the dependence of the order parameter with the
coupling strength indicates that the fully synchronized state is more easily
attained in random graphs. We next focus on the complete synchronized state and
show that this state is less stable for random geometric graphs than for other
kinds of complex networks. Finally, a rewiring mechanism is proposed as a way
to improve the stability of the fully synchronized state as well as to lower
the value of the coupling strength at which it is achieved. Our work has
important implications for the synchronization of wireless networks, and should
provide valuable insights for the development and deployment of more efficient
and robust distributed synchronization protocols for these systems.Comment: 5 pages, 4 figure
No-tillage permanent bed planting and controlled traffic in a maize-cotton irrigated system under Mediterranean conditions: Effects on soil compaction, crop performance and carbon sequestration
11 páginas.-- 8 figuras.-- 2 tablas.-- 66 referenciasUnder irrigated Mediterranean conditions, no-tillage permanent bed planting (PB) is a promising agriculture system for improving soil protection and for soil carbon sequestration. However, soil compaction may increase with time up to levels that reduce crop yield. The aim of this study was to evaluate the mid-term effects of PB on soil compaction, root growth, crop yield and carbon sequestration compared with conventionally tilled bed planting (CB) and with a variant of PB that had partial subsoiling (DPB) in a Typic Xerofluvents soil (Soil Survey Staff, 2010) in southern Spain. Traffic was controlled during the whole study and beds, and furrows with (F+T) and without traffic (F-T), were spatially distinguished during measurements. Comparisons were made during a crop sequence of maize (Zea mays L.)-cotton (Gossypium hirsutum L.)-maize, corresponding to years 4-6 since trial establishment. After six years, soil compaction was higher in PB than in CB, particularly under the bed (44 and 27% higher in top 0.3- and 0.6-m soil layers, respectively). Around this time, maize root density at early grain filling was 17% lower in PB than in CB in the top 0.6-m layer. In DPB, the subsoiling operation was not effective in increasing root density. Nevertheless, root density appeared to maintain above-ground growth and yield in both PB and DPB compared to CB. Furthermore, at the end of the study, more soil organic carbon was stocked in PB than in CB and the difference increased significantly with a depth down to 0.5 m (5.7 Mg ha-1 increment for the top 0.5-m soil layer). Residues tended to accumulate on furrows, and this resulted in spatial and temporal differences in superficial soil organic carbon concentration (SOC) in the permanent planting systems. In PB, SOC in the top 0.05-m layer increased with time faster in furrows than on beds, and reached higher stable values (1.67 vs. 1.09% values, respectively). In CB, tillage homogenized the soil and reduced SOC in the top 0.05-m layer (average stable value of 0.96% on average for beds and furrows).This work has been supported by the Spanish Ministry of Economy and Competitiveness (Project AGL2010-22050-CO3) and FEDER funds. P. Cid received a grant from the Junta de Ampliación de Estudios (CSIC, Spain).Peer reviewe
Enhancing Transport Efficiency by Hybrid Routing Strategy
Traffic is essential for many dynamic processes on real networks, such as
internet and urban traffic systems. The transport efficiency of the traffic
system can be improved by taking full advantage of the resources in the system.
In this paper, we propose a dual-strategy routing model for network traffic
system, to realize the plenary utility of the whole network. The packets are
delivered according to different "efficient routing strategies" [Yan, et al,
Phys. Rev. E 73, 046108 (2006)]. We introduce the accumulate rate of packets,
{\eta} to measure the performance of traffic system in the congested phase, and
propose the so-called equivalent generation rate of packet to analyze the
jamming processes. From analytical and numerical results, we find that, for
suitable selection of strategies, the dual- strategy system performs better
than the single-strategy system in a broad region of strategy mixing ratio. The
analytical solution to the jamming processes is verified by estimating the
number of jammed nodes, which coincides well with the result from simulation.Comment: 6 pages, 3 figure
Bounds for the time to failure of hierarchical systems of fracture
For years limited Monte Carlo simulations have led to the suspicion that the
time to failure of hierarchically organized load-transfer models of fracture is
non-zero for sets of infinite size. This fact could have a profound
significance in engineering practice and also in geophysics. Here, we develop
an exact algebraic iterative method to compute the successive time intervals
for individual breaking in systems of height in terms of the information
calculated in the previous height . As a byproduct of this method,
rigorous lower and higher bounds for the time to failure of very large systems
are easily obtained. The asymptotic behavior of the resulting lower bound leads
to the evidence that the above mentioned suspicion is actually true.Comment: Final version. To appear in Phys. Rev. E, Feb 199
Local versus Global Knowledge in the Barabasi-Albert scale-free network model
The scale-free model of Barabasi and Albert gave rise to a burst of activity
in the field of complex networks. In this paper, we revisit one of the main
assumptions of the model, the preferential attachment rule. We study a model in
which the PA rule is applied to a neighborhood of newly created nodes and thus
no global knowledge of the network is assumed. We numerically show that global
properties of the BA model such as the connectivity distribution and the
average shortest path length are quite robust when there is some degree of
local knowledge. In contrast, other properties such as the clustering
coefficient and degree-degree correlations differ and approach the values
measured for real-world networks.Comment: Revtex format. Final version appeared in PR
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