共查询到20条相似文献,搜索用时 62 毫秒
1.
H. Fukś A. T. Lawniczak R. Duchesne 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):209-214
We study dynamics of spread of epidemics of SIR
type in a realistic spatially-explicit geographical region, Southern and
Central Ontario, using census data obtained from Statistics Canada, and
examine the role of population mixing in epidemic processes. Our model
incorporates the random nature of disease transmission, the discreteness and
heterogeneity of distribution of host population.We find that introduction
of a long-range interaction destroys spatial correlations very easily if
neighbourhood sizes are homogeneous. For inhomogeneous neighbourhoods, very
strong long-range coupling is required to achieve a similar effect. Our work
applies to the spread of influenza during a single season. 相似文献
2.
N. Ananikian H. Lazaryan M. Nalbandyan 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(7):1-6
On the basis of experimental data on interactions between humans we have investigated the process of epidemic spreading in a social network. We found that the distribution of the number of contacts maintained in one day is exponential. Data on frequency and duration of interpersonal interactions are presented. They allow us to simulate the spread of droplet-/-air-borne infections and to investigate the influence of human dynamics on the epidemic spread. Specifically, we investigated the influence of the distribution of frequency and duration of those contacts on magnitude, epidemic threshold and peak timing of epidemics propagating in respective networks. It turns out that a large increase in the magnitude of an epidemic and a decrease in epidemic threshold are visible if and only if both are taken into account. We have found that correlation between contact frequency and duration strongly influences the effectiveness of control measures like mass immunization campaigns. 相似文献
3.
Disease spread in most biological populations requires the proximity of agents. In populations where the individuals have spatial mobility, the contact graph is generated by the “collision dynamics” of the agents, and thus the evolution of epidemics couples directly to the spatial dynamics of the population. We first briefly review the properties and the methodology of an agent-based simulation (EPISIMS) to model disease spread in realistic urban dynamic contact networks. Using the data generated by this simulation, we introduce the notion of dynamic proximity networks which takes into account the relevant time-scales for disease spread: contact duration, infectivity period, and rate of contact creation. This approach promises to be a good candidate for a unified treatment of epidemic types that are driven by agent collision dynamics. In particular, using a simple model, we show that it can account for the observed qualitative differences between the degree distributions of contact graphs of diseases with short infectivity period (such as air-transmitted diseases) or long infectivity periods (such as HIV). 相似文献
4.
Epidemics in small world networks 总被引:1,自引:0,他引:1
M.M. Telo da Gama A. Nunes 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):205-208
For many infectious diseases, a small-world network on an underlying regular
lattice is a suitable simplified model for the contact structure of the host
population. It is well known that the contact network, described in this
setting by a single parameter, the small-world parameter p, plays an
important role both in the short term and in the long term dynamics of
epidemic spread.
We have studied the effect of the network structure on models of immune
for life diseases and found that in addition to the reduction of the
effective transmission rate, through the screening of infectives, spatial
correlations may strongly enhance the stochastic fluctuations. As a
consequence, time series of unforced Susceptible-Exposed-Infected-Recovered
(SEIR) models provide patterns of recurrent epidemics with realistic
amplitudes, suggesting that these models together with complex networks of
contacts are the key ingredients to describe the prevaccination dynamical
patterns of diseases such as measles and pertussis.
We have also studied the role of the host contact strucuture in
pathogen antigenic variation, through its effect on the
final outcome of an invasion by a viral strain of a population where a
very similar virus is endemic. Similar viral strains are modelled
by the same infection and reinfection parameters, and by a given degree of
cross immunity that represents the antigenic distance between the
competing strains. We have found, somewhat surprisingly, that clustering
on the network decreases the potential to sustain pathogen diversity. 相似文献
5.
B. Dybiec 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(3):377-383
We study an extended and modified SIR model of epidemic spread in which susceptible agents during interactions with infectious
neighbors are exposed to the disease and can consequently become infectious. The studied model is extended to include heterogeneity
of interactions which is modelled assuming random character of the dose accumulated by susceptible agents in every interaction
with infectious neighbors. When the accumulated exposure is larger than the individual’s resistance, an agent becomes infectious
and consequently introduces a new source of an epidemic which is capable of passing the disease further. We study statistical
properties characterizing the course of an epidemic. The examination of the modified SIR model reveals a possible “resonant
activation”-like behavior of the system in the duration of the epidemic outbreak and a possible bistable behavior of the model
with accumulated exposure. Furthermore, the linear scaling of the duration of the epidemic with the system size for a wide
range of the model parameters is recorded. 相似文献
6.
In this paper we present a model
with spatial heterogeneity based on cellular automata (CA). In the
model we consider the relevant heterogeneity of host (susceptible)
mixing and the natural birth rate. We divide the susceptible
population into three groups according to the immunity of each
individual based on the classical susceptible--infected--removed
(SIR) epidemic models, and consider the spread of an infectious
disease transmitted by direct contact among humans and vectors
that have not an incubation period to become infectious. We test
the local stability and instability of the disease-free
equilibrium by the spectrum radii of Jacobian. The simulation
shows that the structure of the nearest neighbour size of the cell
(or the degree of the scale-free networks) plays a very important
role in the spread properties of infectious disease. The positive
equilibrium of the infections versus the neighbour size follows
the third power law if an endemic equilibrium point exists.
Finally, we analyse the feature of the infection waves for the
homogeneity and heterogeneous cases respectively. 相似文献
7.
Considering the spread of an epidemic among a population of mobile agents that can get infected and maintain the infection for a period, we investigate the variation in the homogeneity of the distribution of the epidemic with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that the inhomogeneity of epidemic distribution increases with an increase in τ for very low v, while it decreases with an increase in τ for moderate v. The epidemic distribution also tends to a homogeneous state as both v and α increase. 相似文献
8.
Stochastic epidemics and rumours on finite random networks 总被引:3,自引:0,他引:3
In this paper, we investigate the stochastic spread of epidemics and rumours on networks. We focus on the general stochastic (SIR) epidemic model and a recently proposed rumour model on networks in Nekovee et al. (2007) [3], and on networks with different random structures, taking into account the structure of the underlying network at the level of the degree–degree correlation function. Using embedded Markov chain techniques and ignoring density correlations between neighbouring nodes, we derive a set of equations for the final size of the epidemic/rumour on a homogeneous network that can be solved numerically, and compare the resulting distribution with the solution of the corresponding mean-field deterministic model. The final size distribution is found to switch from unimodal to bimodal form (indicating the possibility of substantial spread of the epidemic/rumour) at a threshold value that is higher than that for the deterministic model. However, the difference between the two thresholds decreases with the network size, n, following a n−1/3 behaviour. We then compare results (obtained by Monte Carlo simulation) for the full stochastic model on a homogeneous network, including density correlations at neighbouring nodes, with those for the approximating stochastic model and show that the latter reproduces the exact simulation results with great accuracy. Finally, further Monte Carlo simulations of the full stochastic model are used to explore the effects on the final size distribution of network size and structure (using homogeneous networks, simple random graphs and the Barabasi–Albert scale-free networks). 相似文献
9.
It was reported by Cummings ef al. [Nature 427 (2004) 344] that there are periodic waves in the spatiotemporal data of epidemics. For understanding the mechanism, we study the epidemic spreading on community networks by both the SIS model and the SIRS model. We find that with the increase of infection rate, the number of total infected nodes may be stabilized at a fixed point, oscillatory waves, and periodic cycles. Moreover, the epidemic spreading in the SIS model can be explained by an analytic map. 相似文献
10.
考虑网络交通流量对病毒传播行为的影响,基于平均场理论研究无标度网络上的病毒免疫策略,提出一种改进的熟人免疫机理.理论分析表明,在考虑网络交通流量影响的情况下,当免疫节点密度较小时,随机免疫几乎不能降低病毒的传播速率,而对网络实施目标免疫则能够有效抑制病毒的传播,并且选择度最大的节点进行免疫与选择介数最大的节点进行免疫的效果基本相同.研究还发现,对于网络全局信息未知的情况,与经典熟人免疫策略相比,所提出的免疫策略能够获得更好的免疫效果.通过数值仿真对理论分析进行了验证.
关键词:
无标度网络
病毒传播
交通流量
免疫策略 相似文献
11.
In this paper we extend a compartmental model to the case of a homogenous network epidemic model for a study of the dynamics of obese populations. The social epidemic network-based approach developed here uses different algorithms and points of views regarding the simulation of the dynamics of the network. First, Monte Carlo simulations for homogeneous networks using a traditional constant probability transition rates and a mean-field-like approach are presented. We show that these networks evolve towards an approximately stationary state, which coincides with the one obtained by the underlying classical compartmental continuous model. A mean-field-like approach is applied in order to reduce the large computation time required when dealing with large contact networks. We also investigate, using homogenous contact networks, the effect of the realistic assumption that the waiting times between subpopulations follow a gamma distribution instead of the traditional exponential distribution. It is concluded that careful attention must be paid to the distributions assumed for the state periods. 相似文献
12.
The ubiquity of portable wireless-enabled computing and communications devices has stimulated the emergence of malicious codes (wireless worms) that are capable of spreading between spatially proximal devices. The potential exists for worms to be opportunistically transmitted between devices as they move around, so human mobility patterns will have an impact on epidemic spread. The scenario we address in this paper is proximity attacks from fleetingly in-contact wireless devices with short-range communication range, such as Bluetooth-enabled smart phones.An individual-based model of mobile devices is introduced and the effect of population characteristics and device behaviour on the outbreak dynamics is investigated. The model uses straight-line motion to achieve population, though it is recognised that this is a highly simplified representation of human mobility patterns. We show that the contact rate can be derived from the underlying mobility model and, through extensive simulation, that mass-action epidemic models remain applicable to worm spreading in the low density regime studied here. The model gives useful analytical expressions against which more refined simulations of worm spread can be developed and tested. 相似文献
13.
A model based on a thermodynamic approach is proposed for predicting the dynamics of communicable epidemics assumed to be governed by controlling eforts of multiple scales so that an entropy is associated with the system.All the epidemic details are factored into a single and time-dependent coefcient,the functional form of this coefcient is found through four constraints,including notably the existence of an inflexion point and a maximum.The model is solved to give a log-normal distribution for the spread rate,for which a Shannon entropy can be defined.The only parameter,that characterizes the width of the distribution function,is uniquely determined through maximizing the rate of entropy production.This entropy-based thermodynamic(EBT)model predicts the number of hospitalized cases with a reasonable accuracy for SARS in the year 2003.This EBT model can be of use for potential epidemics such as avian influenza and H7N9 in China. 相似文献
14.
Considering the epidemic spread among a population of mobile agents which can get infected and maintain the infection for a period, we investigate the variation of the homogeneity of the epidemic distribution with the remaining time of infection τ, the velocity modulus of the agent v, and the infection rate α. We find that the distribution of the infected cluster size is always exponential. By analyzing the variation of the characteristic infected cluster size coefficient, we show that, the inhomogeneity of the epidemic distribution increases with the increase of τ for very low v, while decreases with the increase of τ for moderate v. And the epidemic distribution tends to a homogeneous state as both v and α increase. 相似文献
15.
Grain segregation mechanism in aeolian sand ripples 总被引:2,自引:0,他引:2
H.A. Makse 《The European physical journal. E, Soft matter》2000,1(2-3):127-135
Many sedimentary rocks are formed by migration of sand ripples. Thin layers of coarse and fine sand are present in these rocks,
and understanding how layers in sandstone are created has been a longstanding question. Here, we propose a mechanism for the
origin of the most common layered sedimentary structures such as inverse graded climbing ripple lamination and cross-stratification
patterns. The mechanism involves a competition between three segregation processes: (i) size-segregation and (ii) shape-segregation
during transport and rolling, and (iii) size segregation due to different hopping lengths of the small and large grains. We
develop a discrete model of grain dynamics which incorporates the coupling between moving grains and the static sand surface,
as well as the different properties of grains, such as size and roughness, in order to test the plausibility of this physical
mechanism.
Received 19 July 1999 and Received in final form 4 August 1999 相似文献
16.
We propose a modified susceptible-infected-refractory-susceptible (SIRS) model to investigate the global oscillations of the epidemic spreading inWatts-Strogatz (WS) small-world networks. It is found that when an individual immunity does not change or decays slowly in an immune period, the system can exhibit complex transition from an infecting stationary state to a large amplitude sustained oscillation or an absorbing state with no infection. When the immunity decays rapidly in the immune period, the transition to the global oscillation disappears and there is no oscillation. Furthermore, based on thespatio-temporal evolution patterns and the phase diagram, it is disclosed that a long immunity period takes an important role in the emergence of the global oscillation in small-world networks. 相似文献
17.
基于元胞自动机,研究传播延迟对复杂网络病毒传播动力学行为的影响,提出一种新的易染状态-感染状态-易染状态(SIS)传播模型.研究表明,传播延迟的存在显著降低了网络的传播临界值,增强了网络中病毒爆发的危险性.研究还发现,随着传播延迟的增大,病毒的感染程度以及传播速率都明显增大.此外,SIS传播模型不仅能够反映病毒的平均传播趋势,而且可以描述病毒随时间的动态演化过程以及病毒的爆发和消亡等概率事件,从而有效地克服了利用平均场方法构建的微分方程模型只能反映病毒平均传播趋势的局限性.同时,还给出有效控制网络中病毒传
关键词:
复杂网络
病毒传播
元胞自动机
传播延迟 相似文献
18.
We investigate the effects of delaying the time to recovery (delayed recovery) and of nonuniform transmission on the propagation of diseases on structured populations. Through a mean-field approximation and large-scale numerical simulations, we find that postponing the transition from the infectious to the recovered states can largely reduce the epidemic threshold, therefore promoting the outbreak of epidemics. On the other hand, if we consider nonuniform transmission among individuals, the epidemic threshold increases, thus inhibiting the spreading process. When both mechanisms are at work, the latter might prevail, hence resulting in an increase of the epidemic threshold with respect to the standard case, in which both ingredients are absent. Our findings are of interest for a better understanding of how diseases propagate on structured populations and to a further design of efficient immunization strategies. 相似文献
19.
We study the susceptible–infected–recovered (SIR) model in complex networks, considering that not all individuals in the population interact in the same way. This heterogeneity between contacts is modeled by a continuous disorder. In our model, the disorder represents the contact time or the closeness between individuals. We find that the duration time of an epidemic has a crossover with the system size, from a power-law regime to a logarithmic regime depending on the transmissibility related to the strength of the disorder. Using percolation theory, we find that the duration of the epidemic scales as the average length of the branches of the infection. Our theoretical findings, supported by simulations, explains the crossover between the two regimes. 相似文献
20.
M. Medo J. Smrek 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):273-278
We investigate a network model based on an infinite regular
square lattice embedded in the Euclidean plane where the node
connection probability is given by the geometrical distance of
nodes. We show that the degree distribution in the basic model
is sharply peaked around its mean value. Since the model was
originally developed to mimic the social network of
acquaintances, to broaden the degree distribution we propose
its generalization. We show that when heterogeneity is
introduced to the model, it is possible to obtain fat tails of
the degree distribution. Meanwhile, the small-world phenomenon
present in the basic model is not affected. To support our
claims, both analytical and numerical results are obtained. 相似文献