4,858 research outputs found
A stochastic SIRI epidemic model with LĂ©vy noise
Some diseases such as herpes, bovine and human tuberculosis exhibit
relapse in which the recovered individuals do not acquit permanent immunity
but return to infectious class. Such diseases are modeled by SIRI models.
In this paper, we establish the existence of a unique global positive solution
for a stochastic epidemic model with relapse and jumps. We also investigate
the dynamic properties of the solution around both disease-free and endemic
equilibria points of the deterministic model. Furthermore, we present some
numerical results to support the theoretical work
Spatial Epidemics: Critical Behavior in One Dimension
In the simple mean-field SIS and SIR epidemic models, infection is
transmitted from infectious to susceptible members of a finite population by
independent p-coin tosses. Spatial variants of these models are proposed, in
which finite populations of size N are situated at the sites of a lattice and
infectious contacts are limited to individuals at neighboring sites. Scaling
laws for these models are given when the infection parameter p is such that the
epidemics are critical. It is shown that in all cases there is a critical
threshold for the numbers initially infected: below the threshold, the epidemic
evolves in essentially the same manner as its branching envelope, but at the
threshold evolves like a branching process with a size-dependent drift. The
corresponding scaling limits are super-Brownian motions and Dawson-Watanabe
processes with killing, respectively
Weak convergence of marked point processes generated by crossings of multivariate jump processes. Applications to neural network modeling
We consider the multivariate point process determined by the crossing times
of the components of a multivariate jump process through a multivariate
boundary, assuming to reset each component to an initial value after its
boundary crossing. We prove that this point process converges weakly to the
point process determined by the crossing times of the limit process. This holds
for both diffusion and deterministic limit processes. The almost sure
convergence of the first passage times under the almost sure convergence of the
processes is also proved. The particular case of a multivariate Stein process
converging to a multivariate Ornstein-Uhlenbeck process is discussed as a
guideline for applying diffusion limits for jump processes. We apply our
theoretical findings to neural network modeling. The proposed model gives a
mathematical foundation to the generalization of the class of Leaky
Integrate-and-Fire models for single neural dynamics to the case of a firing
network of neurons. This will help future study of dependent spike trains.Comment: 20 pages, 1 figur
Copepods encounter rates from a model of escape jump behaviour in turbulence
A key ecological parameter for planktonic copepods studies is their
interspecies encounter rate which is driven by their behaviour and is strongly
influenced by turbulence of the surrounding environment. A distinctive feature
of copepods motility is their ability to perform quick displacements, often
dubbed jumps, by means of powerful swimming strokes. Such a reaction has been
associated to an escape behaviour from flow disturbances due to predators or
other external dangers. In the present study, the encounter rate of copepods in
a developed turbulent flow with intensity comparable to the one found in
copepods' habitat is numerically investigated. This is done by means of a
Lagrangian copepod (LC) model that mimics the jump escape reaction behaviour
from localised high-shear rate fluctuations in the turbulent flows. Our
analysis shows that the encounter rate for copepods of typical perception
radius of ~ {\eta}, where {\eta} is the dissipative scale of turbulence, can be
increased by a factor up to ~ 100 compared to the one experienced by passively
transported fluid tracers. Furthermore, we address the effect of introducing in
the LC model a minimal waiting time between consecutive jumps. It is shown that
any encounter-rate enhancement is lost if such time goes beyond the dissipative
time-scale of turbulence, {\tau}_{\eta}. Because typically in the ocean {\eta}
~ 0.001m and {\tau}_{\eta} ~ 1s, this provides stringent constraints on the
turbulent-driven enhancement of encounter-rate due to a purely mechanical
induced escape reaction.Comment: 11 pages, 10 figure
Bosonic reaction-diffusion processes on scale-free networks
Reaction-diffusion processes can be adopted to model a large number of
dynamics on complex networks, such as transport processes or epidemic
outbreaks. In most cases, however, they have been studied from a fermionic
perspective, in which each vertex can be occupied by at most one particle.
While still useful, this approach suffers from some drawbacks, the most
important probably being the difficulty to implement reactions involving more
than two particles simultaneously. Here we introduce a general framework for
the study of bosonic reaction-diffusion processes on complex networks, in which
there is no restriction on the number of interacting particles that a vertex
can host. We describe these processes theoretically by means of continuous time
heterogeneous mean-field theory and divide them into two main classes: steady
state and monotonously decaying processes. We analyze specific examples of both
behaviors within the class of one-species process, comparing the results
(whenever possible) with the corresponding fermionic counterparts. We find that
the time evolution and critical properties of the particle density are
independent of the fermionic or bosonic nature of the process, while
differences exist in the functional form of the density of occupied vertices in
a given degree class k. We implement a continuous time Monte Carlo algorithm,
well suited for general bosonic simulations, which allow us to confirm the
analytical predictions formulated within mean-field theory. Our results, both
at the theoretical and numerical level, can be easily generalized to tackle
more complex, multi-species, reaction-diffusion processes, and open a promising
path for a general study and classification of this kind of dynamical systems
on complex networks.Comment: 15 pages, 7 figure
Fluctuation effects in metapopulation models: percolation and pandemic threshold
Metapopulation models provide the theoretical framework for describing
disease spread between different populations connected by a network. In
particular, these models are at the basis of most simulations of pandemic
spread. They are usually studied at the mean-field level by neglecting
fluctuations. Here we include fluctuations in the models by adopting fully
stochastic descriptions of the corresponding processes. This level of
description allows to address analytically, in the SIS and SIR cases, problems
such as the existence and the calculation of an effective threshold for the
spread of a disease at a global level. We show that the possibility of the
spread at the global level is described in terms of (bond) percolation on the
network. This mapping enables us to give an estimate (lower bound) for the
pandemic threshold in the SIR case for all values of the model parameters and
for all possible networks.Comment: 14 pages, 13 figures, final versio
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