529,192 research outputs found
From brain to earth and climate systems: Small-world interaction networks or not?
We consider recent reports on small-world topologies of interaction networks
derived from the dynamics of spatially extended systems that are investigated
in diverse scientific fields such as neurosciences, geophysics, or meteorology.
With numerical simulations that mimic typical experimental situations we have
identified an important constraint when characterizing such networks:
indications of a small-world topology can be expected solely due to the spatial
sampling of the system along with commonly used time series analysis based
approaches to network characterization
Quantifying long-range correlations in complex networks beyond nearest neighbors
We propose a fluctuation analysis to quantify spatial correlations in complex
networks. The approach considers the sequences of degrees along shortest paths
in the networks and quantifies the fluctuations in analogy to time series. In
this work, the Barabasi-Albert (BA) model, the Cayley tree at the percolation
transition, a fractal network model, and examples of real-world networks are
studied. While the fluctuation functions for the BA model show exponential
decay, in the case of the Cayley tree and the fractal network model the
fluctuation functions display a power-law behavior. The fractal network model
comprises long-range anti-correlations. The results suggest that the
fluctuation exponent provides complementary information to the fractal
dimension
Analysis and minimization of bending losses in discrete quantum networks
We study theoretically the transfer of quantum information along bends in
two-dimensional discrete lattices. Our analysis shows that the fidelity of the
transfer decreases considerably, as a result of interactions in the
neighbourhood of the bend. It is also demonstrated that such losses can be
controlled efficiently by the inclusion of a defect. The present results are of
relevance to various physical implementations of quantum networks, where
geometric imperfections with finite spatial extent may arise as a result of
bending, residual stress, etc
The effects of spatial constraints on the evolution of weighted complex networks
Motivated by the empirical analysis of the air transportation system, we
define a network model that includes geographical attributes along with
topological and weight (traffic) properties. The introduction of geographical
attributes is made by constraining the network in real space. Interestingly,
the inclusion of geometrical features induces non-trivial correlations between
the weights, the connectivity pattern and the actual spatial distances of
vertices. The model also recovers the emergence of anomalous fluctuations in
the betweenness-degree correlation function as first observed by Guimer\`a and
Amaral [Eur. Phys. J. B {\bf 38}, 381 (2004)]. The presented results suggest
that the interplay between weight dynamics and spatial constraints is a key
ingredient in order to understand the formation of real-world weighted
networks
Hydrological controls on river network connectivity
This study proposes a probabilistic approach for the quantitative assessment of reach- and network-scale hydrological connectivity as dictated by river flow space–time variability. Spatial dynamics of daily streamflows are estimated based on climatic and morphological features of the contributing catchment, integrating a physically based approach that accounts for the stochasticity of rainfall with a water balance framework and a geomorphic recession flow analysis. Ecologically meaningful minimum stage thresholds are used to evaluate the connectivity of individual stream reaches, and other relevant network-scale connectivity metrics. The framework allows a quantitative description of the main hydrological causes and the ecological consequences of water depth dynamics experienced by river networks. The analysis shows that the spatial variability of local-scale hydrological connectivity is strongly affected by the spatial and temporal distribution of climatic variables. Depending on the underlying climatic settings and the critical stage threshold, loss of connectivity can be observed in the headwaters or along the main channel, thereby originating a fragmented river network. The proposed approach provides important clues for understanding the effect of climate on the ecological function of river corridors
On the Spatial Pattern of Input-Output Metrics for a Network Synchronization Process
A graph-theoretic analysis is undertaken for a compendium of input-output
(transfer) metrics of a standard discrete-time linear synchronization model,
including lp gains, frequency responses, frequency-band energy, and Markov
parameters. We show that these transfer metrics exhibit a spatial degradation,
such that they are monotonically nonincreasing along vertex cutsets away from
an exogenous input. We use this spatial analysis to characterize
signal-to-noise ratios (SNRs) in diffusive networks driven by process noise,
and to develop a notion of propagation stability for dynamical networks.
Finally, the formal results are illustrated through an example
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