85,804 research outputs found
Spatio-temporal Patterns of Indian Monsoon Rainfall
The primary objective of this paper is to analyze a set of canonical spatial
patterns that approximate the daily rainfall across the Indian region, as
identified in the companion paper where we developed a discrete representation
of the Indian summer monsoon rainfall using state variables with
spatio-temporal coherence maintained using a Markov Random Field prior. In
particular, we use these spatio-temporal patterns to study the variation of
rainfall during the monsoon season. Firstly, the ten patterns are divided into
three families of patterns distinguished by their total rainfall amount and
geographic spread. These families are then used to establish `active' and
`break' spells of the Indian monsoon at the all-India level. Subsequently, we
characterize the behavior of these patterns in time by estimating probabilities
of transition from one pattern to another across days in a season. Patterns
tend to be `sticky': the self-transition is the most common. We also identify
most commonly occurring sequences of patterns. This leads to a simple seasonal
evolution model for the summer monsoon rainfall. The discrete representation
introduced in the companion paper also identifies typical temporal rainfall
patterns for individual locations. This enables us to determine wet and dry
spells at local and regional scales. Lastly, we specify sets of locations that
tend to have such spells simultaneously, and thus come up with a new
regionalization of the landmass
Spatial and Temporal Patterns of the Macrobenthic Assemblages in Relation to Environmental Variables
This study focuses on the effect of fallowing of southern blue-fin tuna farms in southern Spencer Gulf, South Australia, on macrobenthic assemblage comparing spatial and temporal patterns of distribution and abundance at eight control sites and eight fallowed pontoon sites, during the period October 2002 to October 2003. Two stations at each site were sampled five times throughout the year with four replicates. Polychaetes were the most abundant organisms both at control sites (76.4%) and fallowed pontoon sites (80.5%). Five dominant taxa (Capitellidae, Cirratullidae, Lumbrineridae, Nephtyidae, and Spionidae), relatively tolerant to organic enrichment, were generally recorded in higher numbers at the fallowed sites than at control sites.Assessed using univariate and multivariate analyses, a significant difference in abundance between the control and fallowed pontoon sites was found, which also showed a significant effect of time. A slight decreased in diversity, number of taxa, and evenness at fallowed pontoon sites compared to those at control sites was observed. Seasonal fluctuations caused by natural variability, especially hydrodynamic conditions and sediment characteristics, are likely to be responsible for the observed changes of the assemblages
Spatio-temporal patterns in the Hantavirus infection
We present a model of the infection of Hantavirus in deer mouse, Peromyscus
maniculatus, based on biological observations of the system in the North
American Southwest. The results of the analysis shed light on relevant
observations of the biological system, such as the sporadical disappearance of
the infection, and the existence of foci or ``refugia'' that perform as
reservoirs of the virus when environmental conditions are less than optimal.Comment: 6 pages, 5 inlined figures, RevTeX 4 forma
Detecting multineuronal temporal patterns in parallel spike trains
We present a non-parametric and computationally efficient method that detects spatiotemporal firing patterns and pattern sequences in parallel spike trains and tests whether the observed numbers of repeating patterns and sequences on a given timescale are significantly different from those expected by chance. The method is generally applicable and uncovers coordinated activity with arbitrary precision by comparing it to appropriate surrogate data. The analysis of coherent patterns of spatially and temporally distributed spiking activity on various timescales enables the immediate tracking of diverse qualities of coordinated firing related to neuronal state changes and information processing. We apply the method to simulated data and multineuronal recordings from rat visual cortex and show that it reliably discriminates between data sets with random pattern occurrences and with additional exactly repeating spatiotemporal patterns and pattern sequences. Multineuronal cortical spiking activity appears to be precisely coordinated and exhibits a sequential organization beyond the cell assembly concept
Spatial and spatio-temporal patterns in a cell-haptotaxis model
We investigate a cell-haptotaxis model for the generation of spatial and spatio-temporal patterns in one dimension. We analyse the steady state problem for specific boundary conditions and show the existence of spatially hetero-geneous steady states. A linear analysis shows that stability is lost through a Hopf bifurcation. We carry out a nonlinear multi-time scale perturbation procedure to study the evolution of the resulting spatio-temporal patterns. We also analyse the model in a parameter domain wherein it exhibits a singular dispersion relation
Spatio-temporal patterns driven by autocatalytic internal reaction noise
The influence that intrinsic local density fluctuations can have on solutions
of mean-field reaction-diffusion models is investigated numerically by means of
the spatial patterns arising from two species that react and diffuse in the
presence of strong internal reaction noise. The dynamics of the Gray-Scott (GS)
model with constant external source is first cast in terms of a continuum field
theory representing the corresponding master equation. We then derive a
Langevin description of the field theory and use these stochastic differential
equations in our simulations. The nature of the multiplicative noise is
specified exactly without recourse to assumptions and turns out to be of the
same order as the reaction itself, and thus cannot be treated as a small
perturbation. Many of the complex patterns obtained in the absence of noise for
the GS model are completely obliterated by these strong internal fluctuations,
but we find novel spatial patterns induced by this reaction noise in regions of
parameter space that otherwise correspond to homogeneous solutions when
fluctuations are not included.Comment: 12 pages, 18 figure
The dynamical strength of social ties in information spreading
We investigate the temporal patterns of human communication and its influence
on the spreading of information in social networks. The analysis of mobile
phone calls of 20 million people in one country shows that human communication
is bursty and happens in group conversations. These features have opposite
effects in information reach: while bursts hinder propagation at large scales,
conversations favor local rapid cascades. To explain these phenomena we define
the dynamical strength of social ties, a quantity that encompasses both the
topological and temporal patterns of human communication
Spatio-Temporal Patterns for a Generalized Innovation Diffusion Model
We construct a model of innovation diffusion that incorporates a spatial
component into a classical imitation-innovation dynamics first introduced by F.
Bass. Relevant for situations where the imitation process explicitly depends on
the spatial proximity between agents, the resulting nonlinear field dynamics is
exactly solvable. As expected for nonlinear collective dynamics, the imitation
mechanism generates spatio-temporal patterns, possessing here the remarkable
feature that they can be explicitly and analytically discussed. The simplicity
of the model, its intimate connection with the original Bass' modeling
framework and the exact transient solutions offer a rather unique theoretical
stylized framework to describe how innovation jointly develops in space and
time.Comment: 20 pages, 4 figure
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