382 research outputs found
Correlations between climate network and relief data
Peer reviewedPublisher PD
Correlations between climate network and relief data
Peer reviewedPublisher PD
Statistical pairwise interaction model of stock market
Financial markets are a classical example of complex systems as they comprise
many interacting stocks. As such, we can obtain a surprisingly good description
of their structure by making the rough simplification of binary daily returns.
Spin glass models have been applied and gave some valuable results but at the
price of restrictive assumptions on the market dynamics or others are
agent-based models with rules designed in order to recover some empirical
behaviours. Here we show that the pairwise model is actually a statistically
consistent model with observed first and second moments of the stocks
orientation without making such restrictive assumptions. This is done with an
approach based only on empirical data of price returns. Our data analysis of
six major indices suggests that the actual interaction structure may be thought
as an Ising model on a complex network with interaction strengths scaling as
the inverse of the system size. This has potentially important implications
since many properties of such a model are already known and some techniques of
the spin glass theory can be straightforwardly applied. Typical behaviours, as
multiple equilibria or metastable states, different characteristic time scales,
spatial patterns, order-disorder, could find an explanation in this picture.Comment: 11 pages, 8 figure
Spectral Theory of Sparse Non-Hermitian Random Matrices
Sparse non-Hermitian random matrices arise in the study of disordered
physical systems with asymmetric local interactions, and have applications
ranging from neural networks to ecosystem dynamics. The spectral
characteristics of these matrices provide crucial information on system
stability and susceptibility, however, their study is greatly complicated by
the twin challenges of a lack of symmetry and a sparse interaction structure.
In this review we provide a concise and systematic introduction to the main
tools and results in this field. We show how the spectra of sparse
non-Hermitian matrices can be computed via an analogy with infinite dimensional
operators obeying certain recursion relations. With reference to three
illustrative examples --- adjacency matrices of regular oriented graphs,
adjacency matrices of oriented Erd\H{o}s-R\'{e}nyi graphs, and adjacency
matrices of weighted oriented Erd\H{o}s-R\'{e}nyi graphs --- we demonstrate the
use of these methods to obtain both analytic and numerical results for the
spectrum, the spectral distribution, the location of outlier eigenvalues, and
the statistical properties of eigenvectors.Comment: 60 pages, 10 figure
Refining trait resilience: identifying engineering, ecological, and adaptive facets from extant measures of resilience
The current paper presents a new measure of trait resilience derived from three common
mechanisms identified in ecological theory: Engineering, Ecological and Adaptive (EEA)
resilience. Exploratory and confirmatory factor analyses of five existing resilience scales
suggest that the three trait resilience facets emerge, and can be reduced to a 12-item scale.
The conceptualization and value of EEA resilience within the wider trait and well-being psychology
is illustrated in terms of differing relationships with adaptive expressions of the traits
of the five-factor personality model and the contribution to well-being after controlling for
personality and coping, or over time. The current findings suggest that EEA resilience is a
useful and parsimonious model and measure of trait resilience that can readily be placed
within wider trait psychology and that is found to contribute to individual well-bein
Bayesian analysis of Jolly-Seber type models; Incorporating heterogeneity in arrival and departure
We propose the use of finite mixtures of continuous distributions in modelling the process by which new individuals, that arrive in groups, become part of a wildlife population. We demonstrate this approach using a data set of migrating semipalmated sandpipers (Calidris pussila) for which we extend existing stopover models to allow for individuals to have different behaviour in terms of their stopover duration at the site. We demonstrate the use of reversible jump MCMC methods to derive posterior distributions for the model parameters and the models, simultaneously. The algorithm moves between models with different numbers of arrival groups as well as between models with different numbers of behavioural groups. The approach is shown to provide new ecological insights about the stopover behaviour of semipalmated sandpipers but is generally applicable to any population in which animals arrive in groups and potentially exhibit heterogeneity in terms of one or more other processes
Legumes as food ingredient: characterization, processing, and applications
Editores: Jiménez-López, José Carlos (CSIC); Clemente, Alfonso (CSIC
Constraints on the intergalactic magnetic field using Fermi-LAT and H.E.S.S. blazar observations
Magnetic fields in galaxies and galaxy clusters are believed to be the result
of the amplification of intergalactic seed fields during the formation of
large-scale structures in the universe. However, the origin, strength, and
morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower
limits on (or indirect detection of) the IGMF can be obtained from observations
of high-energy gamma rays from distant blazars. Gamma rays interact with the
extragalactic background light to produce electron-positron pairs, which can
subsequently initiate electromagnetic cascades. The -ray signature of
the cascade depends on the IGMF since it deflects the pairs. Here we report on
a new search for this cascade emission using a combined data set from the Fermi
Large Area Telescope and the High Energy Stereoscopic System. Using
state-of-the-art Monte Carlo predictions for the cascade signal, our results
place a lower limit on the IGMF of G for a coherence
length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed.
This improves on previous lower limits by a factor of 2. For longer duty cycles
of () yr, IGMF strengths below G
( G) are excluded, which rules out specific models for IGMF
generation in the early universe.Comment: 20 pages, 7 figures, 4 tables. Accepted for publication in ApJ
Letters. Auxiliary data is provided in electronic format at
https://zenodo.org/record/801431
Optical Dissection of Neural Circuits Responsible for Drosophila Larval Locomotion with Halorhodopsin
Halorhodopsin (NpHR), a light-driven microbial chloride pump, enables silencing of neuronal function with superb temporal and spatial resolution. Here, we generated a transgenic line of Drosophila that drives expression of NpHR under control of the Gal4/UAS system. Then, we used it to dissect the functional properties of neural circuits that regulate larval peristalsis, a continuous wave of muscular contraction from posterior to anterior segments. We first demonstrate the effectiveness of NpHR by showing that global and continuous NpHR-mediated optical inhibition of motor neurons or sensory feedback neurons induce the same behavioral responses in crawling larvae to those elicited when the function of these neurons are inhibited by Shibirets, namely complete paralyses or slowed locomotion, respectively. We then applied transient and/or focused light stimuli to inhibit the activity of motor neurons in a more temporally and spatially restricted manner and studied the effects of the optical inhibition on peristalsis. When a brief light stimulus (1–10 sec) was applied to a crawling larva, the wave of muscular contraction stopped transiently but resumed from the halted position when the light was turned off. Similarly, when a focused light stimulus was applied to inhibit motor neurons in one or a few segments which were about to be activated in a dissected larva undergoing fictive locomotion, the propagation of muscular constriction paused during the light stimulus but resumed from the halted position when the inhibition (>5 sec) was removed. These results suggest that (1) Firing of motor neurons at the forefront of the wave is required for the wave to proceed to more anterior segments, and (2) The information about the phase of the wave, namely which segment is active at a given time, can be memorized in the neural circuits for several seconds
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