arXiv subjects

Zhigui Lin

Publications and source records attributed to Zhigui Lin.

34 records · Page 2Linked to original sources

arXiv2020

Spatial diffusion and periodic evolving of domain in an SIS epidemic model

In order to explore the impact of periodically evolving domain on the transmission of disease, we study a SIS reaction-diffusion model with logistic term on a periodically evolving domain. The basic reproduction number ${\mathcal{R}}_0$ is given by the next generation infection operator, and relies on the evolving rate of the periodically evolving domain, diffusion coefficient of infected individuals $d_I$ and size of the space. The monotonicity of ${\mathcal{R}}_0$ with respect to $d_I$, evolving rate $ρ(t)$ and interval length $L$ are derived, and asymptotic property of ${\mathcal{R}}_0$ if $d_I$ or $L$ is small enough or large enough in one-dimensional space are discussed. ${\mathcal{R}}_0$ as threshold can be used to characterize whether the disease-free equilibrium is stable or not. Our theoretical results and numerical simulations indicate that small evolving rate, small diffusion of infected individuals and small interval length have positive impact on prevention and control of disease.

math.AP↗

arXiv2020

Four-tier response system and spatial propagation of COVID-19 in China by a network model

In order to investigate the effectiveness of lockdown and social distancing restrictions, which have been widely carried out as policy choice to curb the ongoing COVID-19 pandemic around the world, we formulate and discuss a staged and weighed networked system based on a classical SEAIR epidemiological model. Five stages have been taken into consideration according to four-tier response to Public Health Crisis, which comes from the National Contingency Plan in China. Staggered basic reproduction number has been derived and we evaluate the effectiveness of lockdown and social distancing policies under different scenarios among 19 cities/regions in mainland China. Further, we estimate the infection risk associated with the sequential release based on population mobility between cities and the intensity of some non-pharmaceutical interventions. Our results reveal that Level I public health emergency response is necessary for high-risk cities, which can flatten the COVID-19 curve effectively and quickly. Moreover, properly designed staggered-release policies are extremely significant for the prevention and control of COVID-19, furthermore, beneficial to economic activities and social stability and development.

physics.soc-ph↗

arXiv2020

Dynamics of a diffusive competitive model on a periodically evolving domain

In this paper, we are concerned with a two-species competitive model with diffusive terms on a periodically evolving domain and study the impact of the spatial periodic evolution on the dynamics of the model. The Lagrangian transformation approach is adopted to convert the model from a changing domain to a fixed one with the assumption that the evolution of habitat is uniform and isotropic. The ecological reproduction indexes of the linearized model are given as thresholds to reveal the dynamic behaviour of the competitive model by discussing the relations between the initial boundary value problem and its corresponding periodic problem. Our theoretical results show that a lager evolving rate benefits the persistence of competitive populations for both sides in the long run. Numerical experiments illustrate that two competitive species, one of which survive and the other vanish on a fixed domain, both survive on a domain with a large evolving rate and both vanish on a domain with a small evolving rate.

math.AP↗

arXiv2020

Effects of depth and evolving rate on phytoplankton growth in a periodically evolving environment

In this paper, we consider a single phytoplankton species which relies on the light for maintaining the metabolism of life in a periodically evolving environment, where the light intensity and the death rate depend on the water column depth triggered by seasonal variation. Based on the basic reproduction number $\mathcal{R}_0$, a threshold type result on the dynamics of the model is established. Especially, various features of $\mathcal{R}_0$ with respect to the vertical turbulent diffusion rate, the buoyant or sinking rate, and the evolving rate of water column depth are derived. Our theoretical results and numerical simulations show that big evolving rate, vertical diffusion rate and water column depth all have an adverse effect on survival of phytoplankton.

math.AP↗

arXiv2018

The spatial-temporal risk index and spreading dynamics for a time-periodic diffusive WNv model

This paper is concerned with a simplified epidemic model for West Nile virus in a heterogeneous time-periodic environment. By means of the model, we will explore the impact of spatial heterogeneity of environment and temporal periodicity on the persistence and eradication of West Nile virus. The free boundary is employed to represent the moving front of the infected region. The basic reproduction number $R_0^D$ and the spatial-temporal risk index $R_0^F(t)$, which depend on spatial heterogeneity, temporal periodicity and spatial diffusion, are defined by considering the associated linearized eigenvalue problem. Sufficient conditions for the spreading and vanishing of West Nile virus are presented for the spatial dynamics of the virus.

math.AP↗

arXiv2017

The invasive dynamics of Aedes aegypti mosquito in a heterogenous environment

A reaction-diffusion-advection model is proposed and investigated to understand the invasive dynamics of Aedes aegypti mosquitoes. The free boundary is introduced to model the expanding front of the invasive mosquitoes in a heterogenous environment. The threshold $R^D_0$ for the model with Dirichlet boundary condition is defined and the threshold $R^F_0(t)$ for the free boundary problem is introduced, and the long-time behavior of positive solutions to the reaction-diffusion-advection system is discussed. Sufficient conditions for the mosquitoes to be eradicated or to spread are given. We show that, if $R^F_0(\infty)\leq 1$, the mosquitoes always vanish, and if $R^F_0(t_0)\geq 1$ for some $t_0\geq 0$, the mosquitoes must spread, while if $R^F_0(0)<1<R^F_0(\infty)$, the spreading or vanishing of the mosquitoes depends on the initial number of mosquitoes, or mosquitoes' invasive ability on the free boundary.

math.AP↗

arXiv2017

Spatial spreading model and dynamics of West Nile virus in birds and mosquitoes with free boundary

In this paper, a reaction-diffusion system is proposed to model the spatial spreading of West Nile virus in vector mosquitoes and host birds in North America. Infection dynamics are based on a simplified model for cross infection between mosquitoes and birds, and the free boundary is introduced to model and explore the expanding front of the infective region. The spatial-temporal risk index $R_0^F(t)$, which involves time and characters of the region, is defined for the simplified model with the free boundary to compare with other related threshold values, including the usual basic reproduction number $R_0$. Sufficient conditions for the virus to vanish or spread are given. Our results suggest that the virus will be in a scenario of vanishing if $R_0\leq 1$, and the virus will spread to the whole region if $R_{0}^F(t_0)\geq 1$ for some $t_0\geq 0$, while if $R^F_0(0)<1<R_0$, the spreading or vanishing of the virus depends on the initial numbers of infected mosquitoes and birds, the area of the infected region and diffusion rates. Moreover, some remarks on the basic reproduction numbers and the spreading speed are presented and compared.

math.AP↗

arXiv2016

Spreading and vanishing in a West Nile virus model with expanding fronts

In this paper, we study a simplified version of a West Nile virus model discussed by Lewis et al. [28], which was considered as a first approximation for the spatial spread of WNv. The basic reproduction number $R_0$ for the non-spatial epidemic model is defined and a threshold parameter $R_0 ^D$ for the corresponding problem with null Dirichlet boundary condition is introduced. We consider a free boundary problem with coupled system, which describes the diffusion of birds by a PDE and the movement of mosquitoes by a ODE. The risk index $R_0^F (t)$ associated with the disease in spatial setting is represented. Sufficient conditions for the WNv to eradicate or to spread are given. The asymptotic behavior of the solution to system when the spreading occurs are considered. It is shown that the initial number of infected populations, the diffusion rate of birds and the length of initial habitat exhibit important impacts on the vanishing or spreading of the virus. Numerical simulations are presented to illustrate the analytical results.

math.AP↗

arXiv2015

Reproduction numbers and the expanding fronts for a diffusion-advection SIS model in heterogeneous time-periodic environment

This paper deals with a simplified SIS model, which describes the transmission of the disease in time-periodic heterogeneous environment. To understand the impact of spatial heterogeneity of environment and small advection on the persistence and eradication of an infectious disease, the left and right free boundaries are introduced to represent the expanding fronts. The basic reproduction numbers $R_0^D$ and $R_0^F(t)$, which depends on spatial heterogeneity, temporal periodicity and advection, are introduced. A spreading-vanishing dichotomy is established and sufficient conditions for the spreading and vanishing of the disease are given. The asymptotic spreading speeds for the left and right fronts are also presented.

math.AP↗

arXiv2015

A SIS reaction-diffusion-advection model in a low-risk and high-risk domain

A simplified SIS reaction-diffusion-advection model is proposed and investigated to understand the impact of spatial heterogeneity of environment and advection on the persistence and eradication of an infectious disease. The free boundary is introduced to model the contact transmission at the spreading front of the disease. The behavior of positive solutions to a reaction-diffusion-advection system are discussed. The basic reproduction number $R_0^F(t)$ associated with the diseases in the spatial setting is introduced for this diffusive SIS model with the free boundary, we prove that fast diffusion, small expanding rate and small initial infected domain are benefit for the control of the spatial spread of the disease. Sufficient conditions for the disease to be eradicated or to spread are also given, our result shows that the disease will spread to the whole area if there exists a $t_0\geq 0$ such that $R_{0}^F(t_0)\geq 1$, that is, if the spreading domain is high-risk at some time, the disease will continue to spread till the whole area is infected; while if $R_{0}^F(0)<1$, the disease may be vanishing or keep spreading depends on the expanding rate and the initial number of the infective individuals. The spreading speeds are also given when spreading happens, and numerical simulations are also given to illustrate the impacts of the advection and the expanding rate on the spreading fronts.

math.AP↗

arXiv2014

The spreading fronts of an infective environment in a man-environment-man epidemic model

A reaction-diffusion model is investigated to understand infective environments in a man-environment-man epidemic model. The free boundary is introduced to describe the expanding front of an infective environment induced by fecally-orally transmitted disease. The basic reproduction number $R^F_0(t)$ for the free boundary problem is introduced, and the behavior of positive solutions to the reaction-diffusion system is discussed. Sufficient conditions for the bacteria to vanish or spread are given. We show that, if $R_0\leq 1$, the bacteria always vanish, and if $R^F_0(t_0)\geq 1$ for some $t_0\geq 0$, the bacteria must spread, while if $R^F_0(0)<1<R_0$, the spreading or vanishing of the bacteria depends on the initial number of bacteria, the length of the initial habitat, the diffusion rate, and other factors. Moreover, some sharp criteria are given.

math.AP↗

arXiv2014

The spreading front of invasive species in favorable habitat or unfavorable habitat

Spatial heterogeneity and habitat characteristic are shown to determine the asymptotic profile of the solution to a reaction-diffusion model with free boundary, which describes the moving front of the invasive species. A threshold value $R_0^{Fr}(D,t)$ is introduced to determine the spreading and vanishing of the invasive species. We prove that if $R_0^{Fr}(D,t_0)\geq 1$ for some $t_0\geq 0$, the spreading must happen; while if $R_0^{Fr}(D,0)<1$, the spreading is also possible. Our results show that the species in the favorable habitat can establish itself if the diffusion is slow or the occupying habitat is large. In an unfavorable habitat, the species dies out if the initial value of the species is small. However, big initial number of the species is benefit for the species to survive. When the species spreads in the whole habitat, the asymptotic spreading speed is given. Some implications of these theoretical results are also discussed.

math.AP↗

arXiv2013

The diffusive competition model with a free boundary: Invasion of a superior or inferior competitor

In this paper we consider the diffusive competition model consisting of an invasive species with density $u$ and a native species with density $v$, in a radially symmetric setting with free boundary. We assume that $v$ undergoes diffusion and growth in $\R^N$, and $u$ exists initially in a ball $\{r 0$ is a given constant and $u(t,h(t))=0$. Thus the population range of $u$ is the expanding ball $\{r<h(t)\}$, while that for $v$ is $\R^N$. In the case that $u$ is a superior competitor (determined by the reaction terms), we show that a spreading-vanishing dichotomy holds, namely, as $t\to\infty$, either $h(t)\to\infty$ and $(u,v)\to (u^*,0)$, or $\lim_{t\to\infty} h(t)<\infty$ and $(u,v)\to (0,v^*)$, where $(u^*,0)$ and $(0, v^*)$ are the semitrivial steady-states of the system. Moreover, when spreading of $u$ happens, some rough estimates of the spreading speed are also given. When $u$ is an inferior competitor, we show that $(u,v)\to (0,v^*)$ as $t\to\infty$.

math.AP↗

arXiv2013

Different Asymptotic Spreading Speeds Induced by Advection in a Diffusion Problem with Free Boundaries

In this paper, we consider a Fisher-KPP equation with an advection term and two free boundaries, which models the behavior of an invasive species in one dimension space. When spreading happens (that is, the solution converges to a positive constant), we use phase plane analysis and upper/lower solutions to prove that the rightward and leftward asymptotic spreading speeds exist, both are positive constants. Moreover, one of them is bigger and the other is smaller than the spreading speed in the corresponding problem without advection term.

math.AP↗

arXiv2013

An SIR epidemic model with free boundary

An SIR epidemic model with free boundary is investigated. This model describes the transmission of diseases. The behavior of positive solutions to a reaction-diffusion system in a radially symmetric domain is investigated. The existence and uniqueness of the global solution are given by the contraction mapping theorem. Sufficient conditions for the disease vanishing or spreading are given. Our result shows that the disease will not spread to the whole area if the basic reproduction number $R_{0}<1$ or the initial infected radius $h_0$ is sufficiently small even that $R_{0}>1$. Moreover, we prove that the disease will spread to the whole area if $R_{0}>1$ and the initial infected radius $h_0$ is suitably large.

math.AP↗

arXiv2010

Traveling wave solutions for delayed reaction-diffusion systems

This paper is concerned with the traveling waves of delayed reaction-diffusion systems where the reaction function possesses the mixed quasimonotonicity property. By the so-called monotone iteration scheme and Schauder's fixed point theorem, it is shown that if the system has a pair of coupled upper and lower solutions, then there exists at least a traveling wave solution. More precisely, we reduce the existence of traveling waves to the existence of an admissible pair of coupled quasi-upper and quasi-lower solutions which are easy to construct in practice.

math.AP↗