Startseite Analysis of a vector-borne disease model with vector-bias mechanism in advective heterogeneous environment
Artikel Open Access

Analysis of a vector-borne disease model with vector-bias mechanism in advective heterogeneous environment

  • Jiaxing Liu und Jinliang Wang EMAIL logo
Veröffentlicht/Copyright: 15. Oktober 2024

Abstract

This study proposed and analyzed a vector-borne reaction–diffusion–advection model with vector-bias mechanism and heterogeneous parameters in one-dimensional habitat. The basic reproduction number R 0 in connection with principal eigenvalue of elliptic eigenvalue problem is characterized as the role of determining the threshold dynamics of the system. The main objective of this study is to investigate the asymptotic profiles and monotonicity of R 0 with respect to diffusion rates and advection rates under certain conditions. Through exploring the level set of R 0 , we also find that there exists a unique surface separating the dynamics. Our results also reveal that the infected hosts and vectors will aggregate at the downstream end if the ratio of advection rates and diffusion rates is sufficiently large.

MSC 2010: 35K57; 35J57; 35B40; 92D25

1 Introduction

Some well-known vector-borne diseases include mosquito-borne diseases (such as dengue fever, chikungunya, West Nile virus, and malaria) [23,31,32,36] and fly-borne diseases, which have become a major concern for national and social development due to environmental change and urbanization. It seems thus imperative to conduct vaccination, health measures, epidemic surveillance, and isolation of infected hosts to control the spread of disease. In recent years, more and more studies indicate that many factors can cause spatial heterogeneity. Specifically, heterogeneity of habitat plays a crucial role in the spread of infectious diseases [1,4,911,15,16,18,19,21,26,27,33]. Among the aforementioned works, Fitzgibbon et al. [9,10] utilized mathematical models that formulated a reaction–diffusion system on non-coincident domains to investigate the circulation of diseases between two host populations. Moreover, in [11], a diffusive vector-borne disease model was formulated to explore the Zika outbreak in Rio De Janeiro. Magal et al. [21,22] further revisited the model in [11], established the threshold dynamics of the model, and studied a deeper characterization of the basic reproduction number (BRN). Let Ω be a bounded domain in R n with smooth boundary Ω . Let H i H i ( x , t ) , V u V u ( x , t ) , and V i V i ( x , t ) be, respectively, the density of infected hosts, uninfected vectors, and infected vectors at location x and time t ; we list the model studied in [11,21,22]:

t H i δ 1 ( x ) H i = λ ( x ) H i + σ 1 ( x ) H u ( x ) V i , x Ω , t > 0 , t V u δ 2 ( x ) V u = σ 2 ( x ) V u ( x ) H i + β ( x ) ( V u + V i ) μ ( x ) ( V u + V i ) V u , x Ω , t > 0 , t V i δ 2 ( x ) V i = σ 2 ( x ) V u ( x ) H i μ ( x ) ( V u + V i ) V i , x Ω , t > 0 , n H i = n H i = n V i , x Ω , t > 0 , ( H i ( , 0 ) , V u ( , 0 ) , V i ( , 0 ) ) = ( H i 0 , V u 0 , V i 0 ) C ( Ω ¯ ; R + 3 ) ,

where δ 1 ( x ) and δ 2 ( x ) C 1 + α ( Ω ¯ ; R ) represent the diffusion rates of the hosts and vectors, respectively; λ ( x ) represents the loss rate of the infected hosts; μ ( x ) stands for the loss rate of the vectors due to environmental crowding at location x ; σ 1 ( x ) and σ 2 ( x ) denote the transmission rates, respectively; and β ( x ) stands for the breeding rate of the vectors. The flux of new infected hosts is denoted as σ 1 ( x ) H u ( x ) V i , where H u ( x ) is the density of uninfected hosts and is assumed to be (almost) not affected by the epidemic (see also in [3]).

Recent studies [2,29,30] revealed that mosquitoes are more likely to select infected hosts than those who are uninfected to bite (called vector-bias mechanism). Denote by p (resp. l ) the probability that a vector randomly arrives at a host and picks the host if he is infected (resp. uninfected). Based on the works in [11,21,29], Wang and Chen [30] analyzed the following model incorporating vector-bias mechanism and heterogeneous parameters:

(1.1) t H i d 1 ( x ) H i = λ ( x ) H i + a β 1 ( x ) l H u ( x ) V i p H i + l H u ( x ) , x Ω , t > 0 , t V u d 2 ( x ) V u = b β 2 ( x ) p H i V u p H i + l H u ( x ) + α ( x ) ( V u + V i ) μ ( x ) ( V u + V i ) V u , x Ω , t > 0 , t V i d 2 ( x ) V i = b β 2 ( x ) p H i V u p H i + l H u ( x ) μ ( x ) ( V u + V i ) V i , x Ω , t > 0 , n H i = n H i = n V i , x Ω , t > 0 , ( H i ( x , 0 ) , V u ( x , 0 ) , V i ( x , 0 ) ) = ( H i 0 ( x ) , V u 0 ( x ) , V i 0 ( x ) ) C ( Ω ¯ ; R + 3 ) ,

where β 1 ( x ) (resp. β 2 ( x ) ) is the biting rate of infected vectors (resp. uninfected vectors), and a (resp. b ) is the transmission probability from an infected vector (resp. host) to an uninfected host (resp. vector). The main conclusions of [30] concern the stability of the disease-free equilibria and threshold dynamics in terms of the BRN.

The aforementioned works adopt the general reaction–diffusion model to study the spread of vector-borne diseases. But, as is known to all, due to the influence of water flow or wind, hosts and vectors may take passive movement in specific directions under some circumstances, which will bring a useful insight for studying the spread of disease. This phenomenon can be described as advection terms into the model. Based on the model of Allen et al. [1], Cui et al. [6,7], and Cui and Lou [8] considered a reaction–diffusion–advection susceptible-infective-susceptible (SIS) model in a spatially heterogeneous environment, and the asymptotic profiles of the BRN and the aggregation phenomenon of endemic equilibrium (EE) were addressed. It should be pointed out that only one associated eigenvalue problem consisting of one equation was used to determine the stability of the disease-free equilibrium. Furthermore, Zhao et al. [31] formulated a reaction–diffusion–advection model and explored the aggregation phenomenon of EE. Specifically, the asymptotic behaviors and monotonicity of the BRN with respect to (w.r.t.) the advection and diffusion rates were studied.

Inspired by the aforementioned works, it thus imperative to understand the possible impacts of the advection and diffusion rates on the BRN and aggregation phenomenon of EE of the model, although incorporating advection effects can make the analysis more difficult and complex. This study is a continuation of [30], and the main objective of this study is to carry out a thorough analysis on the effect of spatial heterogeneity, diffusion rates, and advection rates in a reaction–diffusion–advection system and to explore the asymptotic profiles and monotonicity of BRN and the level set classification of BRN. Moreover, consider the effects of vector-bias on disease transmission. Consider the model of [30] from another perspective, which can help us to understand the influence of different factors on disease transmission, such as diffusion coefficients, advection coefficients, and vector-bias; through the in-depth analysis and research in this article the conclusions in [30] are supplemented. Compared with the existing results, it should be pointed out that the main innovation of this study is the level set of BRN w.r.t. diffusion and advection rates is classified, the aggregation phenomenon is investigated, and the monotonicity of BRN w.r.t. p l is also obtained.

The remainder of this article is organized as follows: in Section 2, we formulate our model with advection terms and vector-bias and present the the well-posedness, threshold dynamics, asymptotic profiles, classification of level set of the BRN, and aggregation phenomenon of EE. The proof of the main results is given in Section 3. We concluded this article in Section 4.

2 Mathematical model and main results

We revisit the model in [30] in an advective heterogeneous environment. To make things simple, we assume that the diffusion rates of hosts and vectors are positive constants, which are written as d 1 and d 2 , respectively; the advection rates of hosts and vectors are positive constants, which are written as c 1 and c 2 , respectively. All hosts and vectors live in an one-dimensional domain [ 0 , L ] with no-flux boundary condition. Here, x = L (resp. x = 0 ) stands for the downstream (resp. upstream) end of the habitat. Thus, the reaction–diffusion–advection model in this study is given as follows:

(2.1) H i t d 1 H i x x + c 1 H i x = λ ( x ) H i + a β 1 ( x ) l H u ( x ) V i p H i + l H u ( x ) , x ( 0 , L ) , t > 0 , V u t d 2 V u x x + c 2 V u x = α ( x ) ( V u + V i ) μ ( x ) ( V u + V i ) V u b β 2 ( x ) p H i V u p H i + l H u ( x ) , x ( 0 , L ) , t > 0 , V i t d 2 V i x x + c 2 V i x = μ ( x ) ( V u + V i ) V i + b β 2 ( x ) p H i V u p H i + l H u ( x ) , x ( 0 , L ) , t > 0 , d 1 H i x c 1 H i = d 2 V u x c 2 V u = d 2 V i x c 2 V i = 0 , x = 0 , L , t > 0 , H i ( 0 , x ) = υ 1 ( x ) 0 , V u ( 0 , x ) = υ 2 ( x ) 0 , V i ( 0 , x ) = υ 3 ( x ) 0 , x ( 0 , L ) .

For u { H i , V u , V i } , u x and u x x represent the first- and second-order derivatives w.r.t. x , respectively. The other parameters of (2.1) are Hölder continuous functions in C z [ 0 , L ] with z ( 0 , 1 ) . For ease of notations, we introduce the following notations:

R 0 loc ( x ) R 0 v h ( x ) R 0 h v ( x ) and R 0 a R 0 a v h R 0 a h v ,

where

R 0 v h ( x ) = a β 1 ( x ) λ ( x ) , R 0 h v ( x ) = b β 2 ( x ) p l H u ( x ) μ ( x )

and

R 0 a v h = 0 L a β 1 ( x ) d x 0 L λ ( x ) d x , R 0 a h v = 0 L b β 2 ( x ) p V l H u ( x ) d x 0 L μ ( x ) V d x .

Biologically, at location x , R 0 loc ( x ) is called the local BRN of (2.1). Specifically, like in [22], R 0 v h ( x ) (resp. R 0 h v ( x ) ) accounts for the impact of an infected vector (resp. host) on uninfected hosts (resp. vectors). Furthermore, if R 0 a > 1 (resp. R 0 a < 1 ), then the habitat is called a high-risk (resp. low-risk) area.

For any x [ 0 , L ] , we denote by

HR { x ( 0 , L ) : R 0 loc ( x ) > 1 }

the high-risk (HR) sites and

LR { x ( 0 , L ) : R 0 loc ( x ) < 1 }

the low-risk (LR) sites, respectively. Upon these settings, we then consider (2.1) under two scenarios:

  1. (H1) For any x 0 HR and y 0 LR, then x 0 < y 0 Figure 1(a).

  2. (H2) For any x 0 HR and y 0 LR, then x 0 > y 0 Figure 1(b).

Figure 1 
               Schematic representation of 
                     
                        
                        
                           
                              
                                 R
                              
                              
                                 0
                              
                              
                                 loc
                              
                           
                           
                              (
                              
                                 x
                              
                              )
                           
                           ‒
                           1
                        
                        {{\mathfrak{R}}}_{0}^{{\rm{loc}}}\left(x)&#x2012;1
                     
                   in 
                     
                        
                        
                           x
                           ∈
                           
                              (
                              
                                 0
                                 ,
                                 L
                              
                              )
                           
                        
                        x\in \left(0,L)
                     
                  : (a) case (H1) and (b) case (H2).
Figure 1

Schematic representation of R 0 loc ( x ) 1 in x ( 0 , L ) : (a) case (H1) and (b) case (H2).

Remark 2.1

Biologically, (H1) (resp. (H2)) indicate that the upstream and downstream end belong to a high-risk (resp. low-risk) site and a low-risk (resp. high-risk) site, respectively.

For mathematically tractable, we further assume that:

  1. (A1) d 1 , d 2 and c 1 , c 2 satisfy c 1 d 1 = c 2 d 2 = σ .

  2. (A2) For x ( 0 , L ) , HR and LR are nonempty, and R 0 loc ( x ) 1 = 0 has only one solution.

Remark 2.2

Mathematically, (A1) is a technical condition. From a biological perspective, this seems reasonable since the hosts and vectors may employ the proportional mobility strategy. (A2) measures that we can find only one low-risk area and one high-risk area in [ 0 , L ] .

2.1 Well-posedness

To proceed, we set X C ( [ 0 , L ] , R 3 ) , which is the Banach space with the supreme norm and define its positive cone by X + C ( [ 0 , L ] , R + 3 ) . For simplicity, let L ( ( 0 , L ) ) , υ ( υ 1 , υ 2 , υ 3 ) and u ( H i , V u , V i ) . For h { β 1 , β 2 , α , μ , H u } and x [ 0 , L ] , we denote h + = max { h ( x ) } and h = min { h ( x ) } . The main result in this subsection reads as follows.

Theorem 2.1

For every υ X + , system (2.1) admits a nonnegative solution u ( t , ; υ ) on [ 0 , ) × [ 0 , L ] , which is unique and eventually lies in

Ω { u X + 0 H i C 1 e c 1 d 1 L , 0 V u C 2 e c 2 d 2 L , 0 V i C 2 e c 2 d 2 L } ,

for C 1 > 0 and C 2 > 0 . Furthermore, the solution semiflow P ( t ) υ u ( t , ; υ ) has a compact attractor in X + .

2.2 Threshold dynamics

The total vectors V = V u + V i satisfy a diffusive and advection logistic equation, which has a globally stable positive equilibrium V ( x ) (see, e.g., [5]) (for simplicity, let us use V as the abbreviation for V ( x ) ). Obviously, system (2.1) has a trivial equilibrium E 0 = ( 0 , 0 , 0 ) and a semi-trivial equilibrium E 1 = ( 0 , V , 0 ) . Throughout of this study, we denote a β 1 ( x ) as g 1 ( x ) and b β 2 ( x ) p V l H u ( x ) as g 2 ( x ) . Obviously, we can see that linearized system (2.1) at E 1 reads as follows:

(2.2) H ^ i t d 1 H ^ i x x + c 1 H ^ i x = λ ( x ) H ^ i + g 1 ( x ) V ^ i , x ( 0 , L ) , t > 0 , V ^ i t d 2 V ^ i x x + c 2 V ^ i x = μ ( x ) V V ^ i + g 2 ( x ) H ^ i , x ( 0 , L ) , t > 0 , d 1 H ^ i x c 1 H ^ i = d 2 V ^ i x c 2 V ^ i , x = 0 , L , t > 0 .

To derive the BRN of (2.1), we define the operators F , B : Y Y by

F ( x ) = 0 g 1 ( x ) g 2 ( x ) 0 , -B ( x ) = d 1 x 2 c 1 x λ ( x ) 0 0 d 2 x 2 c 2 x μ ( x ) V ,

where Y C ( [ 0 , L ] , R 2 ) and x and x 2 denote the first- and second-order derivative operators w.r.t. x , respectively. Let T ˜ ( t ) be the semigroup generated by d v d t = B v , which is associated with no-flux boundary condition. Let φ ( x ) be the initial distribution of infected components at x and

L [ φ ] ( x ) 0 F ( x ) T ˜ ( t ) φ ( x ) d x .

By [28], the BRN of (2.1) can be defined by

(2.3) R 0 ( d 1 , d 2 , c 1 , c 2 ) = r ( L ) ,

the spectral radius of L . Hence, we have the following conclusions.

Lemma 2.1

Assume that (A1) holds. Let k 0 be the positive eigenvalue of

(2.4) d 1 η 1 x x + c 1 η 1 x + λ ( x ) η 1 = k a β 1 ( x ) η 3 , x ( 0 , L ) , d 2 η 3 x x + c 2 η 3 x + μ ( x ) V η 3 = k b β 2 ( x ) p V l H u ( x ) η 1 , x ( 0 , L ) , d 1 η 1 x + c 1 η 1 = d 2 η 3 x + c 1 η 3 = 0 , x = 0 , L ,

with a positive eigenfunction. Then, k 0 is unique and R 0 = 1 k 0 .

Lemma 2.2

Assume that (A1) holds. We then have sign ( k 1 ) = sign ( R 0 1 ) .

With Lemmas 2.1 and 2.2, the global dynamical results of (2.1) read as follows.

Theorem 2.2

Let R 0 be defined in (2.3). The following statements hold:

  1. E 0 is unstable;

  2. If R 0 < 1 , then E 1 is globally asymptotically stable (g.a.s.) and unstable if R 0 > 1 ;

  3. If R 0 > 1 , then we can find a constant ε > 0 such that

    liminf t H i ( , t ) , V u ( , t ) , V i ( , t ) E i ε , i = 0 , 1 ,

uniformly for x [ 0 , L ] . Furthermore, (2.1) has at least one EE.

In what follows, we will use “system (2.1) is UP-EE” as short form for “system (2.1) is uniformly persistent and admits at least one EE.”

2.3 Asymptotic profiles of R 0

Now, we focus on the characterization of R 0 = R 0 ( d 1 , d 2 , c 1 , c 2 ) . We first characterize the asymptotic profiles of R 0 without advection effect and then investigate the asymptotic profiles of R 0 with advection effect.

2.3.1 For the case c 1 = c 2 = 0

When c 1 = c 2 = 0, we write R 0 of (2.1) as R ˜ 0 = R ˜ 0 ( d 1 , d 2 ) .

Theorem 2.3

If c 1 = c 2 = 0, then

  1. Fix d 2 > 0 . If λ ( x ) C 2 [ 0 , L ] and n λ ( x ) = 0 on x = 0 , L , then R ˜ 0 1 γ 1 as d 1 0 , where γ 1 is the smallest eigenvalue of

    (2.5) d 2 ρ 3 x x + μ ( x ) V ρ 3 = γ 1 2 g 1 ( x ) g 2 ( x ) λ ( x ) ρ 3 , x ( 0 , L ) , ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 , x ( 0 , L ) .

    Moreover, if μ ( x ) V μ V and g 1 ( x ) g 1 are positive constants in ( 0 , L ) , then R ˜ 0 g 1 0 L g 2 ( x ) d x μ V 0 L λ ( x ) d x as d 1 ;

  2. Fix d 1 > 0 . If μ ( x ) V C 2 [ 0 , L ] and n μ ( x ) V = 0 on x = 0 , L , then R ˜ 0 1 γ 2 as d 2 0 , where γ 2 is the smallest eigenvalue of

    (2.6) d 1 ρ 1 x x + λ ( x ) ρ 1 = γ 2 2 g 1 ( x ) g 2 ( x ) μ ( x ) V ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = 0 , x ( 0 , L ) .

    Moreover, if λ ( x ) λ and g 2 ( x ) g 2 are positive constants in ( 0 , L ) , then R ˜ 0 g 2 0 L g 1 ( x ) d x λ 0 L μ ( x ) V d x as d 2 ;

  3. As d 1 0 and d 2 0 , then R ˜ 0 max { R 0 loc ( x ) , x [ 0 , L ] } ;

  4. As d 1 and d 2 0 , then R ˜ 0 R 0 a 1 0 L g 1 ( x ) g 2 ( x ) μ ( x ) V d x 0 L λ ( x ) d x ;

  5. As d 1 0 and d 2 , then R ˜ 0 R 0 a 2 0 L g 1 ( x ) g 2 ( x ) λ ( x ) d x 0 L μ ( x ) V d x ;

  6. As d 1 and d 2 , then R ˜ 0 R 0 a 0 L g 1 ( x ) d x 0 L g 2 ( x ) d x 0 L λ ( x ) d x 0 L μ ( x ) V d x .

Remark 2.3

From Theorem 2.3 ( i ) , we can gain that

R ˜ 0 sup ρ 3 H 1 ( ( 0 , L ) ) , ρ 3 0 0 L g 1 ( x ) g 2 ( x ) λ ( x ) ( ρ 3 ) 2 d x d 2 0 L ( ρ 3 x ) 2 d x + 0 L μ ( x ) V ( ρ 3 ) 2 d x ,

if d 1 tends to zero and d 2 > 0 . Similarly, from (ii), we can obtain

R ˜ 0 sup ρ 1 H 1 ( ( 0 , L ) ) , ρ 1 0 0 L g 1 ( x ) g 2 ( x ) μ ( x ) V ( ρ 1 ) 2 d x d 1 0 L ( ρ 1 x ) 2 d x + 0 L λ ( x ) ( ρ 1 ) 2 d x ,

as d 2 tends to zero and d 1 > 0 . When both d 1 and d 2 tend to zero, we can obtain that R ˜ 0 tends to the maximum of the local BRN as shown in (iii). For Theorem 2.3 (iv) and (v), when d 1 tends to infinity and d 2 tends to zero, R ˜ 0 approaches to 0 L g 1 ( x ) g 2 ( x ) μ ( x ) V d x 0 L λ ( x ) d x , when d 2 is large enough and d 1 is small enough, R ˜ 0 tends to 0 L g 1 ( x ) g 2 ( x ) λ ( x ) d x 0 L μ ( x ) V d x . By (vi), in the case that d 1 and d 2 are sufficiently large, R ˜ 0 tends to R 0 a .

Theorem 2.4

If c 1 = c 2 = 0, λ ( x ) and μ ( x ) V are positive constants in ( 0 , L ) . Then, we have:

  1. If g 2 ( x ) is a constant, then R ˜ 0 is a monotone non-increasing function w.r.t. d 1 . Furthermore, if g 1 ( x ) is non-constant, then R ˜ 0 decreases monotonically w.r.t. d 1 .

  2. If g 1 ( x ) is a constant, then R ˜ 0 is a monotone non-increasing function w.r.t. d 2 . Furthermore, if g 2 ( x ) is non-constant, then R ˜ 0 decreases monotonically w.r.t. d 2 .

Theorem 2.5

If c 1 = c 2 = 0 and g 1 ( x ) g 2 ( x ) for any x [ 0 , L ] , then R ˜ 0 is a monotone non-increasing function of d 1 and d 2 .

Remark 2.4

Theorems 2.4 and 2.5 indicate that under certain conditions, rapid movements of infected vectors or hosts can reduce the risk of disease spread and play a positive effects in disease control. The reason for this may be that it reduces exposure to uninfected hosts.

Theorem 2.6

If c 1 = c 2 = 0, g 1 ( x ) g 2 ( x ) for any x [ 0 , L ] and R 0 v h R 0 h v 1 changes sign in ( 0 , L ) , then

  1. If R 0 a > 1 , then R ˜ 0 > 1 ;

  2. If R 0 a < 1 , then there exists a unique positive point ( d ˜ 1 , d ˜ 2 ) such that R ˜ 0 > 1 for d 1 < d ˜ 1 , d 2 < d ˜ 2 , and R ˜ 0 < 1 for d 1 > d ˜ 1 , d 2 > d ˜ 2 .

Remark 2.5

Theorem 2.6 illustrates that when there are no advection effects, if R 0 a > 1 , the disease will spread; if R 0 a < 1 , whether the disease is break out or not depends on the diffusion rates d 1 and d 2 . More specifically, if the diffusion rates are relatively small to some extent, the disease will spread and the disease will be extinct at relatively large diffusion rates.

2.3.2 For the case c 1 , c 2 > 0

The asymptotic properties of R 0 in the presence of advective effects are as follows:

Theorem 2.7

Assume that (A1) holds. We then have

  1. For d 1 , d 2 > 0 , R 0 R ˜ 0 as c 1 0 and c 2 0 ;

  2. For d 1 , d 2 > 0 , R 0 R 0 loc ( L ) as c 1 and c 2 ;

  3. For c 1 , c 2 > 0 , R 0 R 0 loc ( L ) as d 1 0 and d 2 0 ;

  4. For c 1 , c 2 > 0 , R 0 R 0 a as d 1 and d 2 ;

  5. R 0 R 0 loc ( L ) as c 1 0 , c 2 0 , c 1 2 d 1 , and c 2 2 d 2 .

Remark 2.6

Theorem 2.7 (i) illustrates that when advection rates c 1 and c 2 tend to zero, R 0 tends to R ˜ 0 , i.e., the BRN without advection influence; (ii), (iii), and (v) indicate that if the advection rates dominate compared to diffusion rates, R 0 tends to R 0 loc ( L ) ; (iv) shows that R 0 tends to R 0 a (the spatial average value of local BRN).

2.4 Classification of level set of R 0

With the diffusion rates of hosts and vectors ( d 1 and d 2 ) and advection rates ( c 1 and c 2 ), this subsection is spent on studying the level set classification of BRN.

Let k J ( x ) be the principle eigenvalue of

J ( x ) = e σ x λ ( x ) g 1 ( x ) g 2 ( x ) μ ( x ) V ,

and its positive eigenfunction is denoted by ( e J 1 ( x ) , e J 2 ( x ) ) . Let ( ρ 1 1 , ρ 3 1 ) be the positive eigenfunction of R 0 = 1 of (2.4), and let ( η 1 , η 3 ) = e σ x ( ρ 1 , ρ 3 ) .

Lemma 2.3

Assume that (A1)–(A2) hold. If ( ρ 1 1 ( x ) , ρ 3 1 ( x ) ) = k ( x ) ( e J 1 ( x ) , e J 2 ( x ) ) , x ( 0 , L ) , for some sufficiently smooth positive function k ( x ) , then for x ( 0 , L ) :

  1. Under the case of (H1), ρ 1 x 1 ( x ) < 0 and ρ 3 x 1 ( x ) < 0 ;

  2. Under the case of (H2), ρ 1 x 1 ( x ) > 0 and ρ 3 x 1 ( x ) > 0 .

2.4.1 Classification of dynamics for R 0 a > 1

Theorem 2.8

Under the conditions of Lemma 2.3, assume that (A1)–(A2) hold. For the case that (H1), if R 0 a > 1 , and g 1 ( x ) g 2 ( x ) , x ( 0 , L ) , then for spaces c 1 ( d 1 , d 2 ) and c 2 ( d 1 , d 2 ) , there are unique surfaces

1 = { ( c 1 , Γ 1 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 1 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( 0 , ) 2 }

and

2 = { ( c 2 , Γ 2 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 2 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( 0 , ) 2 } ,

such that, system (2.1) is UP-EE for any c 1 < Γ 1 ( d 1 , d 2 ) or c 2 < Γ 2 ( d 1 , d 2 ) , and E 1 is g.a.s. for any c 1 > Γ 1 ( d 1 , d 2 ) or c 2 > Γ 2 ( d 1 , d 2 ) . Furthermore, Γ 1 ( d 1 , d 2 ) and Γ 2 ( d 1 , d 2 ) : ( 0 , ) 2 ( 0 , ) satisfy

lim d 1 0 , d 2 0 Γ i ( d 1 , d 2 ) = 0 , lim d 1 , d 2 Γ 1 ( d 1 , d 2 ) d 1 = Θ 0 , lim d 1 , d 2 Γ 2 ( d 1 , d 2 ) d 2 = Θ 0 , i = 1 , 2 ,

where Θ 0 is a positive solution of

H ( Θ ) = 0 L e Θ x g 1 ( x ) d x 0 L e Θ x g 2 ( x ) d x 0 L e Θ x λ ( x ) d x 0 L e Θ x μ ( x ) V d x = 0 , Θ [ 0 , ) .

Remark 2.7

From assumption (A1), we know that Γ 2 = d 2 Γ 1 d 1 . For i = 1 , 2 , we defined two regions

Ξ c i S L H = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) < 1 , R 0 loc ( L ) < 1 and R 0 a > 1 }

and

Ξ c i U L H = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) > 1 , R 0 loc ( L ) < 1 and R 0 a > 1 } .

In order to describe Theorem 2.8 more clearly, we use Figure 2 to depict it. Specifically, we can see that when the diffusion rates d 1 and d 2 are fixed and advection rate c 1 (or c 2 ) is sufficiently large, E 1 is g.a.s., and (2.1) is uniformly persistent in connection with sufficiently small c 1 (or c 2 ), i.e., the stability of E 1 will change at least once as c 1 (or c 2 ) varies from 0 to . Correspondingly, the disease will become extinct if c 1 d 1 (or c 2 d 2 ) is large and will outbreak if c 1 d 1 (or c 2 d 2 ) is small.

Figure 2 
                     Classification of dynamics in Theorem 2.8. Here, 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       H
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       >
                                       
                                          
                                             Γ
                                          
                                          
                                             i
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       >
                                       0
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       >
                                       0
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{S&#x2012;LH}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):{c}_{i}\gt {\Gamma }_{i}\left({d}_{1},{d}_{2}),{d}_{1}\gt 0,{d}_{2}\gt 0\right\}
                           
                         and 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       H
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       0
                                       <
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       <
                                       
                                          
                                             Γ
                                          
                                          
                                             i
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       >
                                       0
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       >
                                       0
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{U&#x2012;LH}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):0\lt {c}_{i}\lt {\Gamma }_{i}\left({d}_{1},{d}_{2}),{d}_{1}\gt 0,{d}_{2}\gt 0\right\}
                           
                        , 
                           
                              
                              
                                 i
                                 =
                                 1
                                 ,
                                 2
                              
                              i=1,2
                           
                        : (a) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       1
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{1}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       H
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{S&#x2012;LH}
                           
                        , i.e., the disease will be extinct, and system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       H
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{U&#x2012;LH}
                           
                        , i.e., the disease will be spread and (b) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       2
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{2}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       H
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{U&#x2012;LH}
                           
                         and 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       H
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{S&#x2012;LH}
                           
                        .
Figure 2

Classification of dynamics in Theorem 2.8. Here, Ξ c i S L H = { ( d 1 , d 2 , c i ) : c i > Γ i ( d 1 , d 2 ) , d 1 > 0 , d 2 > 0 } and Ξ c i U L H = { ( d 1 , d 2 , c i ) : 0 < c i < Γ i ( d 1 , d 2 ) , d 1 > 0 , d 2 > 0 } , i = 1 , 2 : (a) in space c 1 ( d 1 , d 2 ) , E 1 is g.a.s. when ( d 1 , d 2 , c 1 ) Ξ c 1 S L H , i.e., the disease will be extinct, and system (2.1) is uniformly persistent when ( d 1 , d 2 , c 1 ) Ξ c 1 U L H , i.e., the disease will be spread and (b) in space c 2 ( d 1 , d 2 ) , system (2.1) is uniformly persistent when ( d 1 , d 2 , c 2 ) Ξ c 2 U L H and E 1 is g.a.s. when ( d 1 , d 2 , c 2 ) Ξ c 2 S L H .

2.4.2 Classification of dynamics for R 0 a < 1

In this section, we explore the classification of R 0 regarding the scenario of R 0 a < 1 . The primary findings can be summarized as follows:

Theorem 2.9

Under the conditions of Lemma 2.3, assume that (A1)–(A2) hold. If R 0 a < 1 , and g 1 ( x ) g 2 ( x ) , x ( 0 , L ) , then there exist unique constants ( d ˜ 1 , d ˜ 2 ) satisfying R ˜ 0 ( d ˜ 1 , d ˜ 2 ) = 1 such that

  1. In the case of (H1), then

    1. As ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) , for spaces c 1 ( d 1 , d 2 ) and c 2 ( d 1 , d 2 ) , there exist unique surfaces

      3 = { ( c 1 , Γ 3 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 3 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) }

      and

      4 = { ( c 2 , Γ 4 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 4 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) } ,

      such that system (2.1)is UP-EE for any c 1 < Γ 3 ( d 1 , d 2 ) or c 2 < Γ 4 ( d 1 , d 2 ) , and E 1 is g.a.s. for any c 1 > Γ 3 ( d 1 , d 2 ) or c 2 > Γ 4 ( d 1 , d 2 ) . Furthermore, Γ i ( d 1 , d 2 ) : ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) ( 0 , ) fulfills

      lim d 1 0 , d 2 0 Γ i ( d 1 , d 2 ) = 0 a n d lim d 1 d ˜ 1 , d 2 d ˜ 2 Γ i ( d 1 , d 2 ) = 0 , i = 3 , 4 ;

    2. As ( d 1 , d 2 ) [ d ˜ 1 , ) × [ d ˜ 2 , ) , E 1 is g.a.s.

  2. In the case of (H2), then

    1. As ( d 1 , d 2 ) ( 0 , d ˜ 1 ] × ( 0 , d ˜ 2 ] , system (2.1) is UP-EE;

    2. As ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) , then for spaces c 1 ( d 1 , d 2 ) and c 2 ( d 1 , d 2 ) , there exist unique surfaces

      5 = { ( c 1 , Γ 5 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 5 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) }

      and

      6 = { ( c 2 , Γ 6 ( d 1 , d 2 ) ) : R 0 ( d 1 , d 2 , Γ 6 ( d 1 , d 2 ) ) = 1 , ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) } ,

      such that when c 1 < Γ 5 ( d 1 , d 2 ) or c 2 < Γ 6 ( d 1 , d 2 ) , E 1 is g.a.s., and when c 1 > Γ 5 ( d 1 , d 2 ) or c 2 > Γ 6 ( d 1 , d 2 ) , system (2.1) is UP-EE. In addition, Γ 5 ( d 1 , d 2 ) and Γ 6 ( d 1 , d 2 ) : ( d ˜ 1 , ) × ( d ˜ 2 , ) ( 0 , ) increase monotonically w.r.t. d 1 and d 2 , and satisfy

      lim d 1 d ˜ 1 + , d 2 d ˜ 2 + Γ j ( d 1 , d 2 ) = 0 , j = 5 , 6 , lim d 1 , d 2 Γ 5 ( d 1 , d 2 ) d 1 = Θ 2

      and

      lim d 1 , d 2 Γ 6 ( d 1 , d 2 ) d 2 = Θ 2 ,

      where Θ 2 is the positive solution of H ( Θ ) , which is defined in Theorem 2.8.

Figure 3 
                     Classification of dynamics in (i) of Theorem 2.9. Here, 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                    
                                 
                                 =
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                       ‒
                                       1
                                    
                                 
                                 ∪
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                       ‒
                                       2
                                    
                                 
                              
                              {\Xi }_{{c}_{i}}^{S&#x2012;LL}={\Xi }_{{c}_{i}}^{S&#x2012;LL&#x2012;1}\cup {\Xi }_{{c}_{i}}^{S&#x2012;LL&#x2012;2}
                           
                        , where 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                       ‒
                                       1
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       >
                                       
                                          
                                             Γ
                                          
                                          
                                             j
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                          
                                          )
                                       
                                       ×
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{S&#x2012;LL&#x2012;1}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):{c}_{i}\gt {\Gamma }_{j}\left({d}_{1},{d}_{2}),\left({d}_{1},{d}_{2})\in \left(0,{\tilde{d}}_{1})\times \left(0,{\tilde{d}}_{2})\right\}
                           
                         and 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                       ‒
                                       2
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       >
                                       0
                                       ,
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          [
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                       ×
                                       
                                          [
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{S&#x2012;LL&#x2012;2}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):{c}_{i}\gt 0,\left({d}_{1},{d}_{2})\in \left[{\tilde{d}}_{1},\infty )\times \left[{\tilde{d}}_{2},\infty )\right\}
                           
                        , and 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       L
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       0
                                       <
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       <
                                       
                                          
                                             Γ
                                          
                                          
                                             j
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                          
                                          )
                                       
                                       ×
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{U&#x2012;LL}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):0\lt {c}_{i}\lt {\Gamma }_{j}\left({d}_{1},{d}_{2}),\left({d}_{1},{d}_{2})\in \left(0,{\tilde{d}}_{1})\times \left(0,{\tilde{d}}_{2})\right\}
                           
                        , 
                           
                              
                              
                                 i
                                 =
                                 1
                                 ,
                                 2
                                 ,
                                 j
                                 =
                                 3
                                 ,
                                 4
                              
                              i=1,2,j=3,4
                           
                        : (a) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       1
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{1}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{S&#x2012;LL}
                           
                        , and system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{U&#x2012;LL}
                           
                         and (b) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       2
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{2}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       L
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{U&#x2012;LL}
                           
                        , and 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       L
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{S&#x2012;LL}
                           
                        .
Figure 3

Classification of dynamics in (i) of Theorem 2.9. Here, Ξ c i S L L = Ξ c i S L L 1 Ξ c i S L L 2 , where Ξ c i S L L 1 = { ( d 1 , d 2 , c i ) : c i > Γ j ( d 1 , d 2 ) , ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) } and Ξ c i S L L 2 = { ( d 1 , d 2 , c i ) : c i > 0 , ( d 1 , d 2 ) [ d ˜ 1 , ) × [ d ˜ 2 , ) } , and Ξ c i U L L = { ( d 1 , d 2 , c i ) : 0 < c i < Γ j ( d 1 , d 2 ) , ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) } , i = 1 , 2 , j = 3 , 4 : (a) in space c 1 ( d 1 , d 2 ) , E 1 is g.a.s. when ( d 1 , d 2 , c 1 ) Ξ c 1 S L L , and system (2.1) is uniformly persistent when ( d 1 , d 2 , c 1 ) Ξ c 1 U L L and (b) in space c 2 ( d 1 , d 2 ) , system (2.1) is uniformly persistent when ( d 1 , d 2 , c 2 ) Ξ c 2 U L L , and E 1 is g.a.s. when ( d 1 , d 2 , c 2 ) Ξ c 2 S L L .

Remark 2.8

To illustrate the dynamical classification in Theorem 2.9(i), we define the regions

Ξ c i S L L = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) < 1 , R 0 loc ( L ) < 1 and R 0 a < 1 }

and

Ξ c i U L L = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) > 1 , R 0 loc ( L ) < 1 and R 0 a < 1 } ,

where i = 1 , 2 . Denote Γ ¯ j max { Γ j ( d 1 , d 2 ) : ( d 1 , d 2 ) [ 0 , d ˜ 1 ] × [ 0 , d ˜ 2 ] } , j = 3 , 4 . Figure 3 depicts the dynamical classification in Theorem 2.9(i), implying that the dynamical classification of R 0 is jointly controlled by diffusion rate and advection rate and not solely by diffusion rate or advection rate. The detailed descriptions are as follows:

In Figure 3, our findings are as follows: if c 1 > Γ ¯ 3 (or c 2 > Γ ¯ 4 ), regardless of d 1 and d 2 , the disease becomes extinct; when c 1 < Γ ¯ 3 (or c 2 < Γ ¯ 4 ), for any sufficiently small or large d 1 and d 2 , E 1 is g.a.s., i.e., the disease will be extinct, and system (2.1) is uniformly persistent if d 1 and d 2 take some intermediate values. In this sense, when the fixed c 1 < Γ ¯ 3 (or c 2 < Γ ¯ 4 ) is adopted and with the increase of d 1 and d 2 , the stability of E 1 will change at least twice. From a biological perspective, both the sufficiently small and large diffusion rate accelerate the extinction of the disease. On the one hand, x = L is a low-risk site ( R 0 loc ( L ) < 1 ), for sufficiently small diffusion rates, under the influence of advection, the hosts and vectors are transported to the downstream end, and the disease will become extinct. On the other hand, for sufficiently large diffusion rates, it is noted that the habit ( 0 , L ) is a low-risk area ( R 0 a < 1 ), and the disease will also become extinct. In addition, in terms of intermediate values of diffusion rate, whether the disease persists or not depends on diffusion and advection rates.

Figure 4 
                     Classification of dynamics in (ii) of Theorem 2.9. Here, 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       H
                                       L
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       <
                                       
                                          
                                             Γ
                                          
                                          
                                             j
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          (
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                       ×
                                       
                                          (
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{S&#x2012;HL}=\{\left({d}_{1},{d}_{2},{c}_{i}):{c}_{i}\lt {\Gamma }_{j}\left({d}_{1},{d}_{2}),\left({d}_{1},{d}_{2})\in \left({\tilde{d}}_{1},\infty )\times \left({\tilde{d}}_{2},\infty )\}
                           
                         and 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                    
                                 
                                 =
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                       ‒
                                       1
                                    
                                 
                                 ∪
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                       ‒
                                       2
                                    
                                 
                              
                              {\Xi }_{{c}_{i}}^{U&#x2012;HL}={\Xi }_{{c}_{i}}^{U&#x2012;HL&#x2012;1}\cup {\Xi }_{{c}_{i}}^{U&#x2012;HL&#x2012;2}
                           
                        , where 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                       ‒
                                       1
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                       >
                                       
                                          
                                             Γ
                                          
                                          
                                             j
                                          
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ,
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          (
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                       ×
                                       
                                          (
                                          
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             ∞
                                          
                                          )
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{U&#x2012;HL&#x2012;1}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):{c}_{i}\gt {\Gamma }_{j}\left({d}_{1},{d}_{2}),\left({d}_{1},{d}_{2})\in \left({\tilde{d}}_{1},\infty )\times \left({\tilde{d}}_{2},\infty )\right\}
                           
                         and 
                           
                              
                              
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             i
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                       ‒
                                       2
                                    
                                 
                                 =
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                       ∈
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   1
                                                
                                             
                                          
                                          )
                                       
                                       ×
                                       
                                          (
                                          
                                             0
                                             ,
                                             
                                                
                                                   
                                                      
                                                         d
                                                      
                                                      
                                                         ˜
                                                      
                                                   
                                                
                                                
                                                   2
                                                
                                             
                                          
                                          )
                                       
                                    
                                    }
                                 
                                 ∪
                                 
                                    {
                                    
                                       
                                          (
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   1
                                                
                                             
                                             ,
                                             
                                                
                                                   d
                                                
                                                
                                                   2
                                                
                                             
                                             ,
                                             
                                                
                                                   c
                                                
                                                
                                                   i
                                                
                                             
                                          
                                          )
                                       
                                       :
                                       
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       =
                                       
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   ˜
                                                
                                             
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       =
                                       
                                          
                                             
                                                
                                                   d
                                                
                                                
                                                   ˜
                                                
                                             
                                          
                                          
                                             2
                                          
                                       
                                    
                                    }
                                 
                              
                              {\Xi }_{{c}_{i}}^{U&#x2012;HL&#x2012;2}=\left\{\left({d}_{1},{d}_{2},{c}_{i}):\hspace{1em}\left({d}_{1},{d}_{2})\in \left(0,{\tilde{d}}_{1})\times \left(0,{\tilde{d}}_{2})\right\}\cup \left\{\left({d}_{1},{d}_{2},{c}_{i}):\hspace{1em}{d}_{1}={\tilde{d}}_{1},{d}_{2}={\tilde{d}}_{2}\right\}
                           
                        , 
                           
                              
                              
                                 i
                                 =
                                 1
                                 ,
                                 2
                                 ,
                                 j
                                 =
                                 5
                                 ,
                                 6
                              
                              i=1,2,j=5,6
                           
                        : (a) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       1
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{1}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       H
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{S&#x2012;HL}
                           
                        , and system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             1
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{1})\in {\Xi }_{{c}_{1}}^{U&#x2012;HL}
                           
                         and (b) in space 
                           
                              
                              
                                 
                                    
                                       c
                                    
                                    
                                       2
                                    
                                 
                                 ‒
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                              
                              {c}_{2}&#x2012;\left({d}_{1},{d}_{2})
                           
                        , 
                           
                              
                              
                                 
                                    
                                       E
                                    
                                    
                                       1
                                    
                                 
                              
                              {E}_{1}
                           
                         is g.a.s. when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       S
                                       ‒
                                       H
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{S&#x2012;HL}
                           
                        , and system (2.1) is uniformly persistent when 
                           
                              
                              
                                 
                                    (
                                    
                                       
                                          
                                             d
                                          
                                          
                                             1
                                          
                                       
                                       ,
                                       
                                          
                                             d
                                          
                                          
                                             2
                                          
                                       
                                       ,
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    )
                                 
                                 ∈
                                 
                                    
                                       Ξ
                                    
                                    
                                       
                                          
                                             c
                                          
                                          
                                             2
                                          
                                       
                                    
                                    
                                       U
                                       ‒
                                       H
                                       L
                                    
                                 
                              
                              \left({d}_{1},{d}_{2},{c}_{2})\in {\Xi }_{{c}_{2}}^{U&#x2012;HL}
                           
                        .
Figure 4

Classification of dynamics in (ii) of Theorem 2.9. Here, Ξ c i S H L = { ( d 1 , d 2 , c i ) : c i < Γ j ( d 1 , d 2 ) , ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) } and Ξ c i U H L = Ξ c i U H L 1 Ξ c i U H L 2 , where Ξ c i U H L 1 = { ( d 1 , d 2 , c i ) : c i > Γ j ( d 1 , d 2 ) , ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) } and Ξ c i U H L 2 = { ( d 1 , d 2 , c i ) : ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) } { ( d 1 , d 2 , c i ) : d 1 = d ˜ 1 , d 2 = d ˜ 2 } , i = 1 , 2 , j = 5 , 6 : (a) in space c 1 ( d 1 , d 2 ) , E 1 is g.a.s. when ( d 1 , d 2 , c 1 ) Ξ c 1 S H L , and system (2.1) is uniformly persistent when ( d 1 , d 2 , c 1 ) Ξ c 1 U H L and (b) in space c 2 ( d 1 , d 2 ) , E 1 is g.a.s. when ( d 1 , d 2 , c 2 ) Ξ c 2 S H L , and system (2.1) is uniformly persistent when ( d 1 , d 2 , c 2 ) Ξ c 2 U H L .

Remark 2.9

To illustrate the dynamical classification in Theorem 2.9(ii), we define the regions

Ξ c i S H L = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) < 1 , R 0 loc ( L ) > 1 and R 0 a < 1 }

and

Ξ c i U H L = { ( d 1 , d 2 , c i ) : R 0 ( d 1 , d 2 , c i ) > 1 , R 0 loc ( L ) > 1 and R 0 a < 1 } ,

where i = 1 , 2 . Figure 4 depicts the dynamical classification in Theorem 2.9(ii). The detailed descriptions are as follows:

In Figure 4, our findings are as follows: the disease will break out as ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) , for any c 1 and c 2 , i.e., regulating the movement of hosts and vectors will not control the spread of disease. When ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) with small enough c 1 (or c 2 ), the disease will be eliminated because the upstream end is located in a low-risk site ( R 0 loc ( 0 ) < 1 ). When ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) with large enough c 1 (or c 2 ), the disease will spread because the downstream end is a high-risk site ( R 0 loc ( L ) > 1 ).

2.5 Aggregation phenomenon of EE

Theorem 2.10

Assume that ( A1 ) holds. Under the case of (H2), there is C 4 > 0 such that for any σ , c 1 2 d 1 , c 2 2 d 2 > C 4 , system (2.1) has at least an EE. We further have

  1. When H i ( L ) > V i ( L ) , then there is C 5 > 0 ensuring that

    (2.7) H i ( x ) H i ( L ) e c 1 d 1 ( L x ) C 5 d 1 c 1 2 e c 1 2 d 1 ( L x ) , x [ 0 , L ] .

  2. When H i ( L ) < V i ( L ) , then there is C 6 > 0 ensuring that

    (2.8) V i ( x ) V i ( L ) e c 2 d 2 ( L x ) C 6 d 2 c 2 2 e c 2 2 d 2 ( L x ) , x [ 0 , L ] .

  3. When H i ( L ) = V i ( L ) , then (2.7) and (2.8) hold.

Theorem 2.11

Under the conditions of Theorem 2.10, we then have

  1. When H i ( L ) > V i ( L ) ,

    (2.9) lim c 1 d 1 , c 1 2 d 1 c 1 d 1 H i ( L ) 0 L H i ( x ) d x = 1 .

  2. When H i ( L ) < V i ( L ) ,

    (2.10) lim c 2 d 2 , c 2 2 d 2 c 2 d 2 V i ( L ) 0 L V i ( x ) d x = 1 .

  3. When H i ( L ) = V i ( L ) , then (2.9) and (2.10) hold.

Remark 2.10

Biologically, both Theorems 2.10 and 2.11 demonstrate that if c 1 d 1 or c 2 d 2 is large enough, then aggregation phenomenon occurs at downstream end x = L .

3 Proof of the main results

3.1 Well-posedness: Proof of Theorem 2.1

Taking a transformation

(3.1) ( H i , V u , V i ) = ( e c 1 d 1 x H ¯ i , e c 2 d 2 x V ¯ u , e c 2 d 2 x V ¯ i )

and plugging it into (2.1) obtains

(3.2) H ¯ i t d 1 H ¯ i x x c 1 H ¯ i x = λ ( x ) H ¯ i + a β 1 ( x ) l H u ( x ) V ¯ i p e c 1 d 1 x H ¯ i + l H u ( x ) , V ¯ u t d 2 V ¯ u x x c 2 V ¯ u x = α ( x ) ( V ¯ u + V ¯ i ) μ 1 ( x ) ( V ¯ u + V ¯ i ) V ¯ u b β 3 ( x ) p H ¯ i V ¯ u p e c 1 d 1 x H ¯ i + l H u ( x ) , V ¯ i t d 2 V ¯ i x x c 2 V ¯ i x = μ 1 ( x ) ( V ¯ u + V ¯ i ) V ¯ i + b β 3 ( x ) p H ¯ i V ¯ u p e c 1 d 1 x H ¯ i + l H u ( x ) ,

for x ( 0 , L ) , t > 0 , with

H ¯ i x = V ¯ u x = V ¯ i x = 0 , x = 0 , L , t > 0 , H ¯ i ( 0 , x ) = e c 1 d 1 x υ 1 ( x ) , V ¯ u ( 0 , x ) = e c 2 d 2 x υ 2 ( x ) , V ¯ i ( 0 , x ) = e c 2 d 2 x υ 3 ( x ) , x ( 0 , L ) ,

where β 3 ( x ) = β 2 ( x ) e c 1 d 1 x , and μ 1 ( x ) = μ ( x ) e c 2 d 2 x . For any υ ¯ ( υ ¯ 1 , υ ¯ 2 , υ ¯ 3 ) = ( e c 1 d 1 x υ 1 , e c 2 d 2 x υ 2 , e c 2 d 2 x υ 3 ) X + , using the local existence theorem of quasi-linear parabolic equations, we can find t m > 0 such that system (3.2) has a unique positive solution on [ 0 , t m ) × ( 0 , L ) with t m < . In the following, we estimate the boundedness of the solution of system (3.2) and thus obtain t m = + .

Denote V ¯ = V ¯ u + V ¯ i , which represents the total density of vectors. Then, V ¯ satisfies

(3.3) V ¯ t d 2 V ¯ x x c 2 V ¯ x = α ( x ) V ¯ μ 1 ( x ) V ¯ 2 , x ( 0 , L ) , t > 0 , V ¯ x = 0 , x = 0 , L , t > 0 , V ¯ ( 0 , x ) = e c 2 d 2 x ( υ 2 ( x ) + υ 3 ( x ) ) = V ¯ 0 ( x ) .

According to [5], system (3.3) admits a unique global classical solution V ¯ satisfying

(3.4) d 2 V ¯ x x c 2 V ¯ x = α ( x ) V ¯ μ 1 ( x ) V ¯ 2 , x ( 0 , L ) , V ¯ x = 0 , x = 0 , L .

Furthermore, for all ( t , x ) ( 0 , ) × [ 0 , L ] , we have V ¯ ( x ) > 0 and lim t V ¯ ( t , ) V ¯ ( x ) = 0 .

Based on equation (3.3), we obtain a constant C 2 = max { V ¯ 0 + , α + μ 1 } , such that

(3.5) V ¯ u , V ¯ i C 2 , for any  υ ¯ X + , t 0 .

Consider the following system:

(3.6) H ˜ i t = d 1 H ˜ i x x + c 1 H ˜ i x λ ( x ) H ˜ i + a β 1 ( x ) C 2 , x ( 0 , L ) , t > 0 , H ˜ i x ( t , 0 ) = H ˜ i x ( t , L ) = 0 , t > 0 .

Using the arguments in [35, Lemma 2.1] and [12, Theorem 2.2], it is readily seen that system (3.6) possesses a unique, global attractive and positive steady state A ( x ) in C ( [ 0 , L ] , R ) . Hence, by the comparison principle, we gain

limsup t H ¯ i ( t , ) limsup t H ˜ i ( t , ) = A ( ) , uniformly in ( 0 , L ) .

Then, we can obtain a constant C 1 = A ( ) > 0 , independent of υ ¯ , such that

(3.7) H ¯ i ( t , x ) C 1 , for any  υ ¯ X + , t [ 0 , t m ) .

Therefore, from (3.5) and (3.7), the solution of (3.2) exists globally and lies in the invariant region Ω ¯ , wherein

Ω ¯ { ( H ¯ i , V ¯ u , V ¯ i ) X + 0 H ¯ i C 1 , 0 V ¯ u C 2 , 0 V ¯ i C 2 } .

Based on the transformation (3.1) and [13], the assertions stated in Theorem 2.1 hold. This completes the proof of Theorem 2.1.

It is easy to see from (3.3) that V ¯ u + V ¯ i = V ¯ or V ¯ u + V ¯ i = 0 . Thus, system (3.2) admits a trivial equilibrium E ¯ 0 = ( 0 , 0 , 0 ) and a semi-trivial equilibrium E ¯ 1 = ( 0 , V ¯ , 0 ) , which in turn implies that system (2.1) has a trivial equilibrium E 0 = ( 0 , 0 , 0 ) and a semi-trivial equilibrium E 1 = ( 0 , V , 0 ) in x [ 0 , L ] with V = e c 2 d 2 x V ¯ .

3.2 Threshold dynamics: Proof of Lemmas 2.1 and 2.2 and Theorem 2.2

Proof of Lemma 2.1

Assume that ( η 1 , η 3 ) is the eigenfunction of k 0 of (2.4), and let ( η 1 , η 3 ) = e σ x ( ρ 1 , ρ 3 ) . By straightforward calculations, ( ρ 1 , ρ 3 ) fulfills

(3.8) d 1 ρ 1 x x c 1 ρ 1 x + λ ( x ) ρ 1 = k 0 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x c 2 ρ 3 x + μ ( x ) V ρ 3 = k 0 g 2 ( x ) ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 .

Like in [28], it is essential to show the uniqueness of k 0 . With the help of [24, Lemma 2.2], let k ¯ 0 be another eigenvalue with positive eigenfunction ( ρ ¯ 1 , ρ ¯ 3 ) such that

(3.9) d 1 ρ ¯ 1 x x c 1 ρ ¯ 1 x + λ ( x ) ρ ¯ 1 = k ¯ 0 g 2 ( x ) ρ ¯ 3 , x ( 0 , L ) , d 2 ρ ¯ 3 x x c 2 ρ ¯ 3 x + μ ( x ) V ρ ¯ 3 = k ¯ 0 g 1 ( x ) ρ ¯ 1 , x ( 0 , L ) , ρ ¯ 1 x ( 0 ) = ρ ¯ 1 x ( L ) = ρ ¯ 3 x ( 0 ) = ρ ¯ 3 x ( L ) = 0 .

Multiplying the η 1 -equation of (2.4) by ρ ¯ 1 and the ρ ¯ 1 -equation of (3.9) by η 1 , respectively, and integrating by parts over ( 0 , L ) , one gains

d 1 0 L η 1 x ρ ¯ 1 x d x c 1 0 L η 1 ρ ¯ 1 x d x + 0 L λ ( x ) η 1 ρ ¯ 1 d x = k 0 0 L g 1 ( x ) η 3 ρ ¯ 1 d x , d 1 0 L η 1 x ρ ¯ 1 x d x c 1 0 L η 1 ρ ¯ 1 x d x + 0 L λ ( x ) η 1 ρ ¯ 1 d x = k ¯ 0 0 L g 2 ( x ) ρ ¯ 3 η 1 d x .

Subtracting the aforementioned two equations gives

(3.10) k 0 0 L g 1 ( x ) η 3 ρ ¯ 1 d x k ¯ 0 0 L g 2 ( x ) ρ ¯ 3 η 1 d x = 0 .

Likewise, we multiply the η 3 -equation of (2.4) by ρ ¯ 3 and the ρ ¯ 3 -equation of (3.9) by η 3 , respectively, yielding that

(3.11) k 0 0 L g 2 ( x ) ρ ¯ 3 η 1 d x k ¯ 0 0 L g 1 ( x ) ρ ¯ 1 η 3 d x = 0 .

Then, combining (3.10) and (3.11), we obtain

( k 0 k ¯ 0 ) 0 L g 1 ( x ) ρ ¯ 1 η 3 d x + 0 L g 2 ( x ) η 1 ρ ¯ 3 d x = 0 .

By the positivity of g i ( x ) , i = 1 , 2 , ρ ¯ j , η j , j = 1 , 3 , k 0 = k ¯ 0 . Then R 0 = 1 k 0 can be directly obtained using the similar method in [28]. This proves Lemma 2.1.□

Proof of Lemma 2.2

Letting ( H ^ i , V ^ u , V ^ i ) ( t , x ) = e k t ( φ , ϕ , ψ ) ( x ) and substituting it into (2.2), we obtain

k φ d 1 φ x x + c 1 φ x + λ ( x ) φ g 1 ( x ) ψ = 0 , x ( 0 , L ) , k ϕ d 2 ϕ x x + c 2 ϕ x α ( x ) ( ϕ + ψ ) + 2 μ ( x ) V ϕ + μ ( x ) V ψ + g 2 ( x ) φ = 0 , x ( 0 , L ) , k ψ d 2 ψ x x + c 2 ψ x g 2 ( x ) φ + μ ( x ) V ψ = 0 , x ( 0 , L ) , d 1 φ x c 1 φ = d 2 ϕ x c 2 ϕ = d 2 ψ x c 2 ψ = 0 , x = 0 , L .

Let ( φ , ϕ , ψ ) ( x ) = e σ x ( φ ¯ , ϕ ¯ , ψ ¯ ) ( x ) , then ( φ ¯ , ϕ ¯ , ψ ¯ ) ( x ) satisfies

(3.12) k φ ¯ d 1 φ ¯ x x c 1 φ ¯ x + λ ( x ) φ ¯ g 1 ( x ) ψ ¯ = 0 , x ( 0 , L ) , k ϕ ¯ d 2 ϕ ¯ x x c 2 ϕ ¯ x α ( x ) ( ϕ ¯ + ψ ¯ ) + 2 μ ( x ) V ϕ ¯ + μ ( x ) V ψ ¯ + g 2 ( x ) φ ¯ = 0 , x ( 0 , L ) , k ψ ¯ d 2 ψ ¯ x x c 2 ψ ¯ x g 2 ( x ) φ ¯ + μ ( x ) V ψ ¯ = 0 , x ( 0 , L ) , φ ¯ x ( 0 ) = φ ¯ x ( L ) = ϕ ¯ x ( 0 ) = ϕ ¯ x ( L ) = ψ ¯ x ( 0 ) = ψ ¯ x ( L ) = 0 .

Consider the following problem:

(3.13) k φ ¯ d 1 φ ¯ x x c 1 φ ¯ x + λ ( x ) φ ¯ g 1 ( x ) ψ ¯ = 0 , x ( 0 , L ) , k ψ ¯ d 2 ψ ¯ x x c 2 ψ ¯ x g 2 ( x ) φ ¯ + μ ( x ) V ψ ¯ = 0 , x ( 0 , L ) , φ ¯ x ( 0 ) = φ ¯ x ( L ) = ψ ¯ x ( 0 ) = ψ ¯ x ( L ) = 0 .

It is thus observed from the Krein-Rutman theorem that problem (3.13) has a unique principal eigenvalue k 1 , i.e., k 1 is real and simple with positive eigenfunction ( φ ¯ , ψ ¯ ) and the real parts of other eigenvalues are strictly smaller than k 1 .

Let k 1 be the principle eigenvalue of the adjoint problem of (3.13), which is associated with positive eigenfunction ( φ ˜ , ψ ˜ ) . Then, ( φ ˜ , ψ ˜ ) fulfills

(3.14) k 1 φ ˜ d 1 φ ˜ x x c 1 φ ˜ x + λ ( x ) φ ˜ g 2 ( x ) ψ ˜ = 0 , x ( 0 , L ) , k 1 ψ ˜ d 2 ψ ˜ x x c 2 ψ ˜ x g 1 ( x ) φ ˜ + μ ( x ) V ψ ˜ = 0 , x ( 0 , L ) , φ ˜ x ( 0 ) = φ ˜ x ( L ) = ψ ˜ x ( 0 ) = ψ ˜ x ( L ) = 0 .

Multiplying the η 1 -equation of (2.4) by φ ˜ and the φ ˜ -equation of (3.14) by η 1 , respectively, and then integrating give

d 1 0 L φ ˜ x η 1 x d x c 1 0 L φ ˜ x η 1 d x + 0 L λ ( x ) φ ˜ η 1 d x = 1 R 0 0 L g 1 ( x ) φ ˜ η 3 d x , x ( 0 , L ) , d 1 0 L φ ˜ x η 1 x d x c 1 0 L φ ˜ x η 1 d x + 0 L λ ( x ) φ ˜ η 1 d x 0 L g 2 ( x ) φ ˜ η 1 d x = k 1 0 L φ ˜ η 1 d x , x ( 0 , L ) .

Subtracting the aforementioned two equations yields that

(3.15) k 1 0 L φ ˜ η 1 d x = 1 R 0 0 L g 1 ( x ) φ ˜ η 3 d x 0 L g 2 ( x ) φ ˜ η 1 d x .

Likewise, relying on the ψ ˜ and η 3 trick onto the second equation of (2.4) and (3.14), we obtain

(3.16) k 1 0 L ψ ˜ η 3 d x = 1 R 0 0 L g 2 ( x ) φ ˜ η 1 d x 0 L g 1 ( x ) φ ˜ η 3 d x .

Combining (3.15) and (3.16) gives

k 1 0 L ψ ˜ η 3 d x + 0 L φ ˜ η 1 d x = 1 R 0 1 0 L g 2 ( x ) ψ ˜ η 1 d x + 0 L g 1 ( x ) φ ˜ η 3 d x .

Since η i , φ ˜ and ψ ˜ , g j , i = 1 , 3 , j = 1 , 2 , are positive on ( 0 , L ) , we have sign ( R 0 1 ) = sign ( k 1 ) . This proves Lemma 2.2.□

Next, we proceed to prove Theorem 2.2.

Proof of (i) of Theorem 2.2

Linearizing system (2.1) at E 0 gives

(3.17) k p 1 d 1 p 1 x x + c 1 p 1 x + λ ( x ) p 1 a β 1 ( x ) p 3 = 0 , x ( 0 , L ) , k p 2 d 2 p 2 x x + c 2 p 2 x α ( x ) ( p 2 + p 3 ) = 0 , x ( 0 , L ) , k p 3 d 2 p 3 x x + c 2 p 3 x = 0 , x ( 0 , L ) , d 1 p 1 x c 1 p 1 = d 2 p 2 x c 2 p 2 = d 2 p 3 x c 2 p 3 = 0 , x = 0 , L .

Let ( p 1 , p 2 , p 3 ) = e σ x ( p ¯ 1 , p ¯ 2 , p ¯ 3 ) . By straightforward calculations, ( p ¯ 1 , p ¯ 2 , p ¯ 3 ) fulfills

(3.18) k p ¯ 1 d 1 p ¯ 1 x x c 1 p ¯ 1 x + λ ( x ) p ¯ 1 a β 1 ( x ) p ¯ 3 = 0 , x ( 0 , L ) , k p ¯ 2 d 2 p ¯ 2 x x c 2 p ¯ 2 x α ( x ) ( p ¯ 2 + p ¯ 3 ) = 0 , x ( 0 , L ) , k p ¯ 3 d 2 p ¯ 3 x x c 2 p ¯ 3 x = 0 , x ( 0 , L ) , p ¯ 1 x ( 0 ) = p ¯ 1 x ( L ) = p ¯ 2 x ( 0 ) = p ¯ 2 x ( L ) = p ¯ 3 x ( 0 ) = p ¯ 3 x ( L ) = 0 .

Denote by k ˜ ( d , c , f ) the principal eigenvalue of

(3.19) k p ¯ 2 d p ¯ 2 x x c p ¯ 2 x f p ¯ 2 = 0 , x ( 0 , L ) , p ¯ 2 x ( 0 ) = p ¯ 2 x ( L ) = 0 ,

where f C ( [ 0 , L ] ) . It is straightforward to see that k ˜ ( d , c , f ) is monotone in the sense that if f 1 f 2 , then k ˜ ( d , c , f 1 ) > k ˜ ( d , c , f 2 ) . Let p ˜ 2 be a positive eigenvector of the eigenvalue k ˜ ( d 2 , c 2 , α ) of (3.19). Obviously, k ˜ ( d 2 , c 2 , α ) is also the eigenvalue of (3.18) with ( 0 , p ˜ 2 , 0 ) . Since k ˜ ( d 2 , c 2 , 0 ) > 0 (see, [4]), E 0 is unstable. This proves (i) of Theorem 2.2.□

Proof of (ii) of Theorem 2.2

From (3.19) and (3.4), we know that k ˜ ( d 2 , c 2 , α μ 1 V ¯ ) = 0 . Hence, k ˜ ( d 2 , c 2 , α 2 μ 1 V ¯ ) = k ˜ ( d 2 , c 2 , α 2 μ 1 e c 2 d 2 x V ) < 0 . It then follows that k ˜ ( d 2 , c 2 , α 2 μ V ) < 0 . Let k be the eigenvalue of (3.12). Obviously, k is also an eigenvalue of

k ϕ ¯ d 2 ϕ ¯ x x c 2 ϕ ¯ x α ( x ) ϕ ¯ + 2 μ ( x ) V ϕ ¯ = 0 , x ( 0 , L ) , ϕ ¯ x ( 0 ) = ϕ ¯ x ( L ) = 0 ,

either (3.13). As k 1 < 0 and k ˜ ( d 2 , c 2 , α 2 μ V ) < 0 , we then obtain that k < 0 . Hence, E 1 is stable. On the other hand, if we let ( φ ¯ 0 , ψ ¯ 0 ) be the positive eigenvector of k 1 > 0 , one can directly obtain from the Fredholm alternative and k ˜ ( d 2 , c 2 , α 2 μ V ) < 0 that the problem

k 1 ϕ ¯ d 2 ϕ ¯ x x c 2 ϕ ¯ x α ( x ) ( ϕ ¯ + ψ ¯ 0 ) + 2 μ ( x ) V ϕ ¯ + μ ( x ) V ψ ¯ 0 + b β 2 ( x ) p V l H u ( x ) φ ¯ 0 = 0 , x ( 0 , L ) , ϕ ¯ x ( 0 ) = ϕ ¯ x ( L ) = 0 ,

admits a unique solution ϕ 0 . Consequently, (3.12) has an eigenvector ( φ 0 , ϕ 0 , ψ 0 ) corresponding to k 1 > 0 . Therefore, E 1 is linearly unstable. Next, we represent that E 1 is globally attractive when R 0 < 1 . Choosing a ε > 0 is small enough such that k 2 = k 1 ε ( d 1 , d 2 , c 1 , c 2 , ) < 0 equipped with a positive eigenvector ( φ ε , ψ ε ) . Recall that as t , V ¯ u + V ¯ i V ¯ on [ 0 , L ] . Based on this, there exists t 0 > 0 such that V ¯ ε < V ¯ u + V ¯ i < V ¯ + ε for x [ 0 , L ] and t > t 0 . Hence, ( H ¯ i , V ¯ i ) of (3.2) is a lower solution of

(3.20) H ˇ i t d 1 H ˇ i x x c 1 H ˇ i x = λ ( x ) H ˇ i + a β 1 ( x ) V ˇ i , x ( 0 , L ) , t > t 0 , V ˇ i t d 2 V ˇ i x x c 2 V ˇ i x = b β 3 ( x ) p ( V ¯ + ε ) l H u ( x ) H ˇ i μ 1 ( x ) ( V ¯ ε ) V ˇ i , x ( 0 , L ) , t > t 0 , H ˇ i x = V ˇ i x = 0 , x = 0 , L , H ˇ i ( x , t 0 ) = φ ε ( x ) , V ˇ i ( x , t 0 ) = ψ ε ( x ) , x ( 0 , L ) ,

where is a large enough positive constant such that ( H ¯ i ( x , t 0 ) , V ¯ i ( x , t 0 ) ) ( φ ε ( x ) , ψ ε ( x ) ) . By the comparison principle, we can conclude that

( H ¯ i , V ¯ i ) ( H ˇ i , V ˇ i ) , for all x [ 0 , L ] and t t 0 .

Due to the fact that (3.20) admits a unique solution ( H ˇ i , V ˇ i ) = ( φ ε ( x ) e k 2 t , ψ ε ( x ) e k 2 t ) . It follows from k 2 < 0 that ( H ˇ i , V ˇ i ) ( 0 , 0 ) uniformly for x [ 0 , L ] as t , and so ( H ¯ i , V ¯ i ) ( 0 , 0 ) does. Furthermore, from (3.3), V ¯ u V ¯ uniformly for x [ 0 , L ] as t . This proves (ii) of Theorem 2.2.□

Proof of (iii) of Theorem 2.2

Similar to the arguments in [30, Lemma 4.2 and Theorem 4.2], following a contradictory argument and the persistence theory (see [20, Theorem 3.7]), we can prove (iii) of Theorem 2.2.□

3.3 Asymptotic behaviors of R 0 with no advection effect: Proof of Theorems 2.3–2.6

Before going into details, we first prove the boundedness of R 0 . By Lemma 2.1, 1 R 0 is the principle eigenvalue of (2.4), i.e.,

(3.21) d 1 η 1 x x + c 1 η 1 x + λ ( x ) η 1 = 1 R 0 g 1 ( x ) η 3 , x ( 0 , L ) , d 2 η 3 x x + c 2 η 3 x + μ ( x ) V η 3 = 1 R 0 g 2 ( x ) η 1 , x ( 0 , L ) , d 1 η 1 x + c 1 η 1 = d 2 η 3 x + c 2 η 3 = 0 , x = 0 , L .

Let us integrate the first two equations of (3.21) by parts over ( 0 , L ) , obtaining that

0 L λ ( x ) η 1 d x = 1 R 0 0 L g 1 ( x ) η 3 d x , x ( 0 , L ) , 0 L μ ( x ) V η 3 d x = 1 R 0 0 L g 2 ( x ) η 1 d x , x ( 0 , L ) .

Thus,

R 0 = 0 L g 1 ( x ) η 3 d x 0 L g 2 ( x ) η 1 d x 0 L λ ( x ) η 1 d x 0 L μ ( x ) V η 3 d x .

Hence, we have the following result on the boundedness of R 0 .

Lemma 3.1

For d 1 > 0 , d 2 > 0 , c 1 > 0 , c 2 > 0 , we then have

( g 1 ) ( g 2 ) λ + μ + V + R 0 ( g 1 ) + ( g 2 ) + λ μ V .

Remark 3.1

By the definition of g 2 ( x ) , it is readily seen that R 0 is a monotonically increasing function w.r.t. p l . Therefore, if the impact of vector-bias mechanism on disease spread is ignored, the risk of disease spread might be undervalued.

3.3.1 Proof of Theorem 2.3

Proof of (i) of Theorem 2.3

When c 1 = c 2 = 0 , (3.9) becomes

(3.22) d 1 ρ ¯ 1 x x + λ ( x ) ρ ¯ 1 = 1 R ˜ 0 g 2 ( x ) ρ ¯ 3 , x ( 0 , L ) , d 2 ρ ¯ 3 x x + μ ( x ) V ρ ¯ 3 = 1 R ˜ 0 g 1 ( x ) ρ ¯ 1 , x ( 0 , L ) , ρ ¯ 1 x ( 0 ) = ρ ¯ 1 x ( L ) = ρ ¯ 3 x ( 0 ) = ρ ¯ 3 x ( L ) = 0 .

For the case that d 1 0 , we choose v ( 0 , 1 ) and letting { a C 2 ( [ 0 , L ] ) a x ( 0 ) = a x ( L ) = 0 } be dense in C ( [ 0 , L ] ) . Hence, there exist two positive functions g ˆ 1 ( x ) , g ˜ 1 ( x ) such that

(3.23) g 1 ( x ) 1 + v < g ˆ 1 ( x ) < g 1 ( x ) < g ˜ 1 ( x ) < g 1 ( x ) 1 v .

Let ( ρ ́ 1 , ρ ́ 3 ) = ( γ 1 g ˆ 1 ( x ) λ ( x ) ρ 3 , ρ 3 ) and ( ρ ̀ 1 , ρ ̀ 3 ) = ( γ 1 g ˜ 1 ( x ) λ ( x ) ρ 3 , ρ 3 ) , where ρ 3 is the positive eigenfunction of (2.5). By (3.23), we can choose a τ > 0 small enough such that for 0 < d 1 < τ , the following statements hold true:

(3.24) d 1 ρ ́ 1 x x + λ ( x ) 1 g 1 ( x ) ( 1 + v ) g ˆ 1 ( x ) ρ ́ 1 0 , x ( 0 , L ) , ρ ́ 1 x ( 0 ) = ρ ́ 1 x ( L ) = 0

and

(3.25) d 1 ρ ̀ 1 x x + λ ( x ) 1 g 1 ( x ) ( 1 v ) g ˜ 1 ( x ) ρ ̀ 1 0 , x ( 0 , L ) , ρ ̀ 1 x ( 0 ) = ρ ̀ 1 x ( L ) = 0 .

Moreover, it follows from (2.5) and (3.24) that

d 2 ρ ́ 3 x x + μ ( x ) V ρ ́ 3 γ 1 g 2 ( x ) ρ ́ 1 d 2 ρ ́ 3 x x + μ ( x ) V ρ ́ 3 γ 1 2 g 1 ( x ) g 2 ( x ) λ ( x ) ρ ́ 3 = 0

and

d 1 ρ ́ 1 x x + λ ( x ) ρ ́ 1 λ ( x ) g 1 ( x ) g ˆ ( 1 + v ) ρ ́ 1 = γ 1 g 1 ( x ) 1 + v ρ ́ 3 .

Thus,

(3.26) d 1 ρ ́ 1 x x + λ ( x ) ρ ́ 1 γ 1 g 1 ( x ) 1 + v ρ ́ 3 , x ( 0 , L ) , d 2 ρ ́ 3 x x + μ ( x ) V ρ ́ 3 γ 1 g 2 ( x ) ρ ́ 1 0 , x ( 0 , L ) , ρ ́ 1 x ( 0 ) = ρ ́ 1 x ( L ) = ρ ́ 3 x ( 0 ) = ρ ́ 3 x ( L ) = 0 .

Multiplying the ρ ́ 1 -inequality of (3.26) by ρ ¯ 1 and the ρ ¯ 1 -equation of (3.22) by ρ ́ 1 respectively, and then integrating by parts over ( 0 , L ) obtain that

d 1 0 L ρ ́ 1 x ρ ¯ 1 x d x + 0 L λ ( x ) ρ ́ 1 ρ ¯ 1 d x γ 1 0 L g 1 ( x ) 1 + v ρ ́ 3 ρ ¯ 1 d x , d 1 0 L ρ ́ 1 x ρ ¯ 1 x d x + 0 L λ ( x ) ρ ́ 1 ρ ¯ 1 d x = 1 R ˜ 0 0 L g 2 ( x ) ρ ¯ 3 ρ ́ 1 d x .

Hence,

(3.27) 0 L 1 R ˜ 0 g 2 ( x ) ρ ¯ 3 ρ ́ 1 γ 1 1 + v g 1 ( x ) ρ ́ 3 ρ ¯ 1 d x 0 .

In a similar manner, we can obtain that

(3.28) 0 L 1 R ˜ 0 g 1 ( x ) ρ ¯ 1 ρ ́ 3 γ 1 g 2 ( x ) ρ ́ 1 ρ ¯ 3 d x 0 .

This, together with (3.27) and (3.28), indicates that

1 R ˜ 0 0 L g 1 ( x ) ρ ¯ 1 ρ ́ 3 d x γ 1 0 L g 2 ( x ) ρ ¯ 3 ρ ́ 1 d x γ 1 R ˜ 0 γ 1 1 + v 0 L g 1 ( x ) ρ ¯ 1 ρ ́ 3 d x ,

i.e.,

1 R ˜ 0 2 γ 1 2 1 + v 0 L g 1 ( x ) ρ ¯ 1 ρ ́ 3 d x 0 .

Since γ 1 > 0 , we then have R ˜ 0 1 + v γ 1 . Furthermore, R ˜ 0 1 v γ 1 with the help of (3.25). This combined with the arbitrariness of v indicates that R ˜ 0 1 γ 1 as d 1 0 .

Next, we consider the case that c 1 = c 2 = 0 and d 1 . With the aid of Lemma 3.1, passing to a sequence if necessary, R ˜ 0 R ˇ 0 as d 1 . Without loss of generality, set ρ 1 + ρ 3 = 1 . From (3.8) and L p estimates, the uniform boundedness of ρ 1 W p 2 ( 0 , L ) and ρ 3 W p 2 ( 0 , L ) directly follows for p > 1 . By appealing to the Sobolev embedding theorem, ρ 1 C 1 ( ( 0 , L ) ) and ρ 3 C 1 ( ( 0 , L ) ) are also uniformly bounded. It comes naturally that there exist positive functions ρ ˙ 1 and ρ ˙ 3 C 1 ( [ 0 , L ] ) such that ( ρ 1 , ρ 3 ) ( ρ ˙ 1 , ρ ˙ 3 ) in C 1 ( [ 0 , L ] ) , as d 1 . Then, ρ ˙ 3 satisfies

d 2 ρ ˙ 3 x x + μ V ρ ˙ 3 g 2 ( x ) R ˇ 0 ρ ˙ 1 = 0 , x ( 0 , L ) , ρ ˙ 3 x ( 0 ) = ρ ˙ 3 x ( L ) = 0 .

Using the elliptic regularity estimate to the ρ 1 -equation of (3.8) when c 1 = c 2 = 0 , we find that ρ ˙ 1 is a constant and ρ ˙ 1 = g 1 0 L ρ ˙ 3 d x R ˇ 0 0 L λ ( x ) d x since g 1 ( x ) g 1 . Thus,

d 2 ρ ˙ 3 x x + μ V ρ ˙ 3 g 2 ( x ) R ˇ 0 g 1 0 L ρ ˙ 3 d x R ˇ 0 0 L λ ( x ) d x = 0 , x ( 0 , L ) , ρ ˙ 3 x ( 0 ) = ρ ˙ 3 x ( L ) = 0 .

Since μ ( x ) V μ V and g 1 ( x ) g 1 are positive constants in ( 0 , L ) ,

R ˜ 0 R ˇ 0 = g 1 0 L g 2 ( x ) d x μ V 0 L λ ( x ) d x , as d 1 .

This proves (i) of Theorem 2.3.□

Proof of (ii) of Theorem 2.3

Similar to the proof of (i) and so is omitted.□

Proof of (iii) of Theorem 2.3

With the aid of Lemma 3.1, passing to a sequence if necessary, R ˜ 0 R ^ 0 as d 1 0 and d 2 0 . It then follows that, for any v ˜ > 0 , we can find an adequately small τ ˜ > 0 such that

(3.29) R ˜ 0 R ^ 0 < v ˜ , for any  d 1 , d 2 ( 0 , τ ˜ ) .

Let the operators B and F be defined in Section 2.2. Let us consider the eigenvalue problem

(3.30) B ϱ 1 θ F ϱ = ϖ 1 ( θ ) ϱ , x ( 0 , L ) , ϱ x = 0 , x = 0 , L ,

where ϱ = ( ϱ 1 , ϱ 3 ) T , θ > 0 , ϖ 1 ( θ ) is the principal eigenvalue of (3.30). From (3.8), B ρ 1 R ˜ 0 F , ρ = 0 , ρ = ( ρ 1 , ρ 3 ) T . It then follows from (3.29) that

B ρ 1 R ^ 0 + v ˜ F ρ 0 B ρ 1 R ^ 0 v ˜ F ρ .

By virtue of [17, Proposition 3.4], we know that

(3.31) ϖ 1 ( R ^ 0 + v ˜ ) ϖ 1 ( R ˜ 0 ) = 0 ϖ 1 ( R ^ 0 v ˜ ) .

Furthermore, from in [17, Theorem 1.4], we obtain

lim d 1 0 , d 2 0 ϖ 1 ( θ ) = ϖ ˆ 1 ( θ ) = max x [ 0 , L ] ( M 1 ( x ) ) ,

where ( M 1 ( x ) ) is the principal eigenvalue of

M 1 ( x ) = λ ( x ) g 1 ( x ) θ g 2 ( x ) θ μ ( x ) V .

Thus,

ϖ ˆ 1 ( θ ) = max x [ 0 , L ] ( M 1 ( x ) ) = > 0 , θ > θ ˆ , = 0 , θ = θ ˆ , < 0 , θ < θ ˆ ,

where θ ˆ max x [ 0 , L ] g 1 ( x ) g 2 ( x ) λ ( x ) μ ( x ) V . Then, sign ( ϖ ˆ 1 ( θ ) ) = sign ( θ θ ˆ ) . By (3.31), one gains θ ˆ v ˜ R ^ 0 θ ˆ + v ˜ . By the arbitrariness of v ˜ , R ˜ 0 max { R 0 loc ( x ) , x [ 0 , L ] } as d 1 , d 2 0 .□

Proof of (iv) of Theorem 2.3

With the similar procedures as the proof of (ii), letting ρ 1 + ρ 3 = 1 and passing to a sequence if necessary, we know that ρ 1 ρ 1 in C 1 ( [ 0 , L ] ) as d 1 and d 2 0 , where ρ 1 0 . Based on this, for any v > 0 , there exists a τ ¯ > 0 such that

g 2 ( x ) R ˜ 0 ( ρ 1 v ) < d 2 ρ 3 x x + μ ( x ) V ρ 3 < g 2 ( x ) R ˜ 0 ( ρ 1 + v ) , x ( 0 , L ) , ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 ,

for any 0 < d 2 , 1 d 1 < τ ¯ , which implies that lim d 2 0 ρ 3 = g 2 ( x ) ρ 1 μ ( x ) V R ˜ 0 . Thus, ρ 1 > 0 owing to ρ 1 + ρ 3 = 1 . Integrating the ρ 1 -equation of (3.8) in ( 0 , L ) , and then letting d 1 and d 2 0 to give R ˜ 0 0 L g 1 ( x ) g 2 ( x ) μ ( x ) V d x 0 L λ ( x ) d x .□

Proof of (v) of Theorem 2.3

Similar to (iv), one can obtain R ˜ 0 0 L g 1 ( x ) g 2 ( x ) λ ( x ) d x 0 L μ ( x ) V d x as d 1 0 and d 2 .□

Proof of (vi) of Theorem 2.3

By applying the assertions in (i), (v), and (iv), (vi) is obvious. This completes the proof of Theorem 2.3.□

3.3.2 Proof of Theorem 2.4

Proof of (i) of Theorem 2.4

When c 1 = c 2 = 0 and λ ( x ) , μ ( x ) V , and g 2 ( x ) are the constants, we rewrite system (3.8) as

(3.32) d 1 ρ 1 x x + λ ρ 1 = 1 R ˜ 0 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x + μ V ρ 3 = 1 R ˜ 0 g 2 ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 .

Similar to the arguments in [14, Lemma 15.1] and [5, Proposition 2.20], we know that R ˜ 0 and the corresponding eigenfunction ( ρ 1 , ρ 3 ) T are analytic functions w.r.t. d 1 and d 2 . Hence, differentiating problem (3.32) by d 1 yields

(3.33) ρ 1 x x d 1 ρ 1 x x + λ ρ 1 = 1 R ˜ 0 g 1 ( x ) ρ 3 R ˜ 0 R ˜ 0 2 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x + μ V ρ 3 = 1 R ˜ 0 g 2 ρ 1 R ˜ 0 R ˜ 0 2 g 2 ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 ,

where represents the derivative of d 1 . From the ρ 3 -equation of (3.32) and ρ 3 -equation of (3.33), we obtain

(3.34) ρ 1 = R ˜ 0 g 2 ( d 2 ρ 3 x x + μ V ρ 3 ) , ρ 1 = R ˜ 0 g 2 d 2 ρ 3 x x + μ V ρ 3 + R ˜ 0 R ˜ 0 2 g 2 ρ 1 .

Multiplying the ρ 1 -equation of (3.33) by ρ 3 and with the help of (3.34) and integrating by parts, we obtain

(3.35) R ˜ 0 R ˜ 0 2 0 L g 1 ( x ) ρ 3 2 d x = R ˜ 0 g 2 0 L [ d 1 ρ 3 x x λ ρ 3 ] d 2 ρ 3 x x + μ V ρ 3 + R ˜ 0 R ˜ 0 2 g 2 ρ 1 d x + R ˜ 0 g 2 0 L ρ 3 x x [ d 2 ρ 3 x x + μ V ρ 3 ] d x + 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x = W 1 + W 2 + W 3 ,

where

W 1 = R ˜ 0 g 2 0 L ρ 3 x x [ d 2 ρ 3 x x + μ V ρ 3 ] d x , W 2 = R ˜ 0 R ˜ 0 0 L [ d 1 ρ 3 x x λ ρ 3 ] ρ 1 d x , W 3 = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x R ˜ 0 g 2 0 L [ d 1 ρ 3 x x + λ ρ 3 ] [ d 2 ρ 3 x x + μ V ρ 3 ] d x .

From the ρ 1 -equation of (3.32), one obtains that W 2 = R ˜ 0 R ˜ 0 2 0 L g 1 ( x ) ρ 3 2 d x by integration. Direct calculation yields that

W 1 = R ˜ 0 d 2 g 2 0 L ρ 3 x x 2 d x R ˜ 0 μ V g 2 0 L ρ 3 x 2 d x ,

i.e., W 1 < 0 . Moreover,

W 3 = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x R ˜ 0 g 2 0 L [ d 1 ρ 3 x x + λ ρ 3 ] [ d 2 ρ 3 x x + μ V ρ 3 ] d x = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x R ˜ 0 g 2 0 L [ d 1 ρ 3 x x + λ ρ 3 ] [ d 2 ρ 3 x x + μ V ρ 3 ] d x = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x 0 L [ d 1 ρ 3 x x + λ ρ 3 ] ρ 1 d x = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x 0 L [ d 1 ρ 1 x x + λ ρ 1 ] ρ 3 d x = 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x 1 R ˜ 0 0 L g 1 ( x ) ρ 3 ρ 3 d x = 0 .

Thus, R ˜ 0 0 , i.e., R ˜ 0 is a monotone non-increasing function w.r.t. d 1 . Additionally, R ˜ 0 = 0 if ρ 3 is a constant in ( 0 , L ) . According to the ρ 3 -equation of (3.32) that ρ 1 is also a constant in ( 0 , L ) . It follows from ρ 1 -equation of (3.32) that g 1 ( x ) is constant in ( 0 , L ) . Therefore, R ˜ 0 decreases monotonically w.r.t. d 1 if g 1 ( x ) is non-constant in ( 0 , L ) .□

Proof of (ii) of Theorem 2.4 is similar to (i).

3.3.3 Proof of Theorem 2.5

Proof of (i) of Theorem 2.5

When c 1 = c 2 = 0 , differentiating system (3.8) by d 1 yields

(3.36) ρ 1 x x d 1 ρ 1 x x + λ ( x ) ρ 1 = 1 R ˜ 0 g 1 ( x ) ρ 3 R ˜ 0 R ˜ 0 2 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x + μ ( x ) V ρ 3 = 1 R ˜ 0 g 2 ( x ) ρ 1 R ˜ 0 R ˜ 0 2 g 2 ( x ) ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 ,

where denotes the derivative w.r.t. d 1 . From the ρ 1 -equations of (3.8) and the ρ 1 -equations of (3.36), we obtain

(3.37) R ˜ 0 R ˜ 0 2 0 L g 1 ( x ) ρ 1 ρ 3 d x = 0 L ρ 1 x 2 d x + 1 R ˜ 0 0 L g 1 ( x ) ( ρ 3 ρ 1 ρ 3 ρ 1 ) d x .

Similarly,

(3.38) R ˜ 0 R ˜ 0 2 0 L g 2 ( x ) ρ 1 ρ 3 d x = 1 R ˜ 0 0 L g 2 ( x ) ( ρ 3 ρ 1 ρ 3 ρ 1 ) d x .

Adding (3.37) and (3.38) and substituting g 1 ( x ) g 2 ( x ) into ( 0 , L ) , we obtain

R ˜ 0 R ˜ 0 2 0 L ( g 1 ( x ) + g 2 ( x ) ) ρ 1 ρ 3 d x = 0 L ρ 1 x 2 d x 0 .

Thus, R ˜ 0 non-increasing monotonically w.r.t. d 1 . This proves (i) of Theorem 2.5.□

Proof of (ii) of Theorem 2.5

(ii) can be proved by the arguments similar to (i), which will not be repeated here.□

3.3.4 Proof of Theorem 2.6

Proof of (i) of Theorem 2.6

Theorem 2.3 tells us that lim d 1 , d 2 R ˜ 0 ( d 1 , d 2 ) = R 0 a > 1 . Thus, from Theorem 2.5, the assertion in (i) of Theorem 2.6 directly follows.□

Proof of (ii) of Theorem 2.6

Combined with the fact that R 0 v h R 0 h v 1 changes sign and Theorem 2.3, (ii) directly follows. This proves Theorem 2.6.□

3.4 Asymptotic behaviors of R 0 with advection effect: Proof of Theorem 2.7

We first prove the following lemmas.

Lemma 3.2

If (A1) holds, then R 0 R 0 loc ( L ) as σ , c 1 2 d 1 and c 2 2 d 2 .

Proof

Let ( η 1 , η 3 ) = e J σ x ( q 1 , q 3 ) in ( 0 , L ) , where σ = c 1 d 1 = c 2 d 2 , ( η 1 , η 3 ) is the positive eigenfunction of 1 R 0 in Lemma 2.1 and J is a undetermined constant. Since ( η 1 , η 3 ) satisfies (2.4), we then have

(3.39) d 1 q 1 x x + c 1 ( 1 2 J ) q 1 x + [ c 1 σ J ( 1 J ) + λ ( x ) ] q 1 = 1 R 0 g 1 ( x ) q 3 , x ( 0 , L ) , d 2 q 3 x x + c 2 ( 1 2 J ) q 3 x + [ c 2 σ J ( 1 J ) + μ ( x ) V ] q 3 = 1 R 0 g 2 ( x ) q 1 , x ( 0 , L ) , d 1 q 1 x ( 0 ) = c 1 ( 1 J ) q 1 ( 0 ) , d 1 q 1 x ( L ) = c 1 ( 1 J ) q 1 ( L ) , d 2 q 3 x ( 0 ) = c 2 ( 1 J ) q 3 ( 0 ) , d 2 q 3 x ( L ) = c 2 ( 1 J ) q 3 ( L ) .

For K 1 > 0 , substituting J = 1 + K 1 d 1 c 1 2 into (3.39) results in

(3.40) d 1 q 1 x x c 1 1 + 2 K 1 d 1 c 1 2 q 1 x + K 1 1 + K 1 d 1 c 1 2 + λ ( x ) q 1 = 1 R 0 g 1 ( x ) q 3 , x ( 0 , L ) , q 1 x ( 0 ) = K 1 c 1 q 1 ( 0 ) , q 1 x ( L ) = K 1 c 1 q 1 ( L ) .

Let q 1 ( x 1 ) = min x [ 0 , L ] q 1 ( x ) . Further from the positivity of q 1 and the boundary condition of (3.40), we know that q 1 x ( 0 ) < 0 , which results in x 1 > 0 . Hence, q 1 x ( x 1 ) = 0 and q 1 x x ( x 1 ) 0 . Hence, from (3.40), one knows that

K 1 1 + K 1 d 1 c 1 2 + λ ( x 1 ) 1 R 0 g 1 ( x 1 ) q 3 ( x 1 ) q 1 ( x 1 ) 0 .

If we make K 1 = λ + for any adequately small d 1 c 1 2 , then

K 1 1 + K 1 d 1 c 1 2 + λ ( x 1 ) 1 R 0 g 1 ( x 1 ) q 3 ( x 1 ) q 1 ( x 1 ) < 0 ,

which is a contradiction. Hence, x 1 = L . It follows that q 1 ( L ) q 1 ( x ) , x [ 0 , L ] , i.e.,

q 1 ( L ) = e c 1 d 1 1 + K 1 d 1 c 1 2 L η 1 ( L ) q 1 ( x ) = e c 1 d 1 1 + K 1 d 1 c 1 2 x η 1 ( x ) .

Furthermore, we have

(3.41) e c 1 d 1 1 + K 1 d 1 c 1 2 ( L x ) η 1 ( x ) η 1 ( L ) , x [ 0 , L ] .

Similarly, if J = 1 + K 2 d 2 c 2 2 and K 2 = μ + V + , we then have

(3.42) e c 2 d 2 ( 1 + K 2 d 2 c 2 2 ) ( L x ) η 3 ( x ) η 3 ( L ) , x [ 0 , L ] .

For K 3 > 0 , substituting J = 1 K 3 d 1 c 1 2 into (3.39) results in

(3.43) d 1 q 1 x x c 1 1 2 K 3 d 1 c 1 2 q 1 x + K 3 1 K 3 d 1 c 1 2 + λ ( x ) q 1 = 1 R 0 g 1 ( x ) q 3 , x ( 0 , L ) , q 1 x ( 0 ) = K 3 c 1 q 1 ( 0 ) , q 1 x ( L ) = K 3 c 1 q 1 ( L ) .

Let q 1 ( x 1 ) = max x [ 0 , L ] q 1 ( x ) . Further from the positivity of q 1 and the boundary condition of (3.43), we know that q 1 x ( 0 ) > 0 , which results in x 1 > 0 . If x 1 ( 0 , L ) , then q 1 x ( x 1 ) = 0 and q 1 x x ( x 1 ) 0 . Thus, by (3.43), we have

K 3 1 K 3 d 1 c 1 2 + λ ( x 1 ) 1 R 0 g 1 ( x 1 ) q 3 ( x 1 ) q 1 ( x 1 ) 0 .

Due to the continuity of g 1 ( ) , q 1 ( ) and q 3 ( ) on [ 0 , L ] , we can find N 1 > 0 such that g 1 ( x 1 ) q 3 ( x 1 ) q 1 ( x 1 ) N 1 . Then, we choose

K 3 = 2 N 1 λ + μ + V + ( g 1 ) ( g 2 ) and d 1 c 1 2 satisfy d 1 c 1 2 < 1 4 N 1 ( g 1 ) ( g 2 ) λ + μ + V + = 1 2 K 3 .

This combined with Lemma 3.1 implies that

K 3 1 K 3 d 1 c 1 2 + λ ( x 1 ) 1 R 0 g 1 ( x 1 ) q 3 ( x 1 ) q 1 ( x 1 ) K 3 1 K 3 d 1 c 1 2 + λ ( x 1 ) N 1 λ + μ + V + ( g 1 ) ( g 2 ) 2 N 1 λ + μ + V + ( g 1 ) ( g 2 ) 1 2 N 1 λ + μ + V + ( g 1 ) ( g 2 ) 1 4 N 1 ( g 1 ) ( g 2 ) λ + μ + V + + λ ( x 1 ) N 1 λ + μ + V + ( g 1 ) ( g 2 ) = λ ( x 1 ) > 0 ,

which is a contradiction. Hence, x 1 = L . It follows that q 1 ( x ) q 1 ( L ) , x [ 0 , L ] , i.e.,

q 1 ( x ) = e c 1 d 1 1 K 3 d 1 c 1 2 x η 1 ( x ) q 1 ( L ) = e c 1 d 1 1 K 3 d 1 c 1 2 L η 1 ( L ) .

Furthermore, we have

(3.44) η 1 ( x ) η 1 ( L ) e c 1 d 1 1 K 3 d 1 c 1 2 ( L x ) , x [ 0 , L ] .

Similarly, let J = 1 K 4 d 2 c 2 2 , where

K 4 = 2 N 2 λ + μ + V + ( g 1 ) ( g 2 ) and d 1 c 1 2 satisfy d 2 c 2 2 < 1 4 N 2 ( g 1 ) ( g 2 ) λ + μ + V + = 1 2 K 4 ,

for some N 2 > 0 . Hence,

(3.45) η 3 ( x ) η 3 ( L ) e c 2 d 2 1 K 4 d 2 c 2 2 ( L x ) , x [ 0 , L ] .

This together with (3.41), (3.44), (3.42), and (3.45) implies that

(3.46) e c 1 d 1 1 + K 1 d 1 c 1 2 ( L x ) η 1 ( x ) η 1 ( L ) e c 1 d 1 1 K 3 d 1 c 1 2 ( L x ) , x [ 0 , L ]

and

(3.47) e c 2 d 2 1 + K 2 d 2 c 1 2 ( L x ) η 3 ( x ) η 3 ( L ) e c 2 d 2 1 K 4 d 2 c 2 2 ( L x ) , x [ 0 , L ] .

Denote ζ = c 1 ( L x ) d 1 = c 2 ( L x ) d 2 . By (3.46) and (3.47), we obtain

(3.48) e 1 + K 1 d 1 c 1 2 ζ η 1 L d 1 c 1 ζ η 1 ( L ) e 1 K 3 d 1 c 1 2 ζ

and

(3.49) e ( 1 + K 2 d 2 c 2 2 ) ζ η 3 L d 2 c 2 ζ η 3 ( L ) e 1 K 4 d 2 c 2 2 ζ , ζ [ 0 , σ L ] .

Let us integrate (2.4) into ( 0 , L ) and then divide them by η 1 ( L ) and η 3 ( L ) , respectively, obtaining that

0 L λ ( x ) η 1 ( x ) η 1 ( L ) d x = 1 R 0 0 L g 1 ( x ) η 3 ( x ) η 1 ( L ) d x , 0 L μ ( x ) V η 3 ( x ) η 3 ( L ) d x = 1 R 0 0 L g 2 ( x ) η 1 ( x ) η 3 ( L ) d x .

Accordingly,

0 L λ ( x ) η 1 ( x ) η 1 ( L ) d x 0 L μ ( x ) V η 3 ( x ) η 3 ( L ) d x = 1 R 0 2 0 L g 1 ( x ) η 3 ( x ) η 3 ( L ) d x 0 L g 2 ( x ) η 1 ( x ) η 1 ( L ) d x .

Since x = L d 1 c 1 ζ = L d 2 c 2 ζ , it follows that

0 σ L λ L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ 0 σ L μ L d 2 c 2 ζ V η 3 L d 2 c 2 ζ η 3 ( L ) d ζ = 1 R 0 2 0 σ L g 1 L d 2 c 2 ζ η 3 L d 2 c 2 ζ η 3 ( L ) d ζ 0 σ L g 2 L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ .

Consequently, R 0 = G 1 ( d 1 , d 2 , c 1 , c 2 ) G 2 ( d 1 , d 2 , c 1 , c 2 ) , where

G 1 ( d 1 , d 2 , c 1 , c 2 ) = 0 σ L g 1 L d 2 c 2 ζ η 3 L d 2 c 2 ζ η 3 ( L ) d ζ 0 σ L g 2 L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ

and

G 2 ( d 1 , d 2 , c 1 , c 2 ) = 0 σ L λ L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ 0 σ L μ L d 2 c 2 ζ V η 3 L d 2 c 2 ζ η 3 ( L ) d ζ .

In virtue of the Lebesgue-dominant convergence theorem and (3.48)–(3.49), we can obtain that

lim c 1 d 1 , c 1 2 d 1 c 2 d 2 , c 2 2 d 2 R 0 = lim c 1 d 1 , c 1 2 d 1 c 2 d 2 , c 2 2 d 2 G 1 ( d 1 , d 2 , c 1 , c 2 ) G 2 ( d 1 , d 2 , c 1 , c 2 ) = lim c 1 d 1 , c 1 2 d 1 c 2 d 2 , c 2 2 d 2 0 σ L g 1 L d 2 c 2 ζ η 3 L d 2 c 2 ζ η 3 ( L ) d ζ 0 σ L g 2 L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ 0 σ L λ L d 1 c 1 ζ η 1 L d 1 c 1 ζ η 1 ( L ) d ζ 0 σ L μ L d 2 c 2 ζ V η 3 L d 2 c 2 ζ η 3 ( L ) d ζ = 0 g 1 ( L ) e ζ d ζ 0 g 2 ( L ) e ζ d ζ 0 λ ( L ) e ζ d ζ 0 μ ( L ) V d ζ = g 1 ( L ) g 2 ( L ) λ ( L ) μ ( L ) V = a β 1 ( L ) b β 2 ( L ) p λ ( L ) μ ( L ) l H u ( L ) = R 0 loc ( L ) .

Lemma 3.3

If (A1) holds. For any fixed c 1 > 0 and c 2 > 0 , R 0 R 0 a as d 1 and d 2 .

Proof

With the aid of Lemma 3.1, passing to a sequence if necessary, R 0 R 0 when d 1 and d 2 . Let ( η 1 , η 3 ) be the positive eigenfunction of 1 R 0 of (2.4). Without loss of generality, set η 1 + η 3 = 1 . By appealing to L p estimate, the Sobolev embedding theorem and elliptic regularity estimate, there exist positive functions η 1 and η 3 C 1 ( [ 0 , L ] ) such that ( η 1 , η 3 ) ( η 1 , η 3 ) in C 1 ( [ 0 , L ] ) , as d 1 and d 2 , where η 1 and η 3 are constants. It then follows from (2.4) and passing to the limit d 1 and d 2 that

η 1 0 L λ ( x ) d x = η 3 1 R 0 0 L g 1 ( x ) d x , η 3 0 L μ ( x ) V d x = η 1 1 R 0 0 L g 2 ( x ) d x .

Direct calculation gives R 0 = R 0 a v h R 0 a h v = R 0 a . This proves Lemma 3.3.□

Proof of Theorem 2.7

(i) is obvious. (ii)–(iii) and (iv) directly follow from Lemmas 3.2 and 3.3. (v) holds from Lemma 3.2, since c 1 d 1 = c 1 2 d 1 c 1 and c 2 d 2 = c 2 2 d 2 c 2 as c 1 2 d 1 , c 1 0 , and c 2 2 d 2 , c 2 0 . This proves Theorem 2.7.□

3.5 Classification of level set of R 0 : Proof of Lemma 2.3 and Theorems 2.8 and 2.9

3.5.1 Proof of Lemma 2.3

By virtue of (A2) and (H1), we can find a x ( 0 , L ) such that R 0 v h ( x ) R 0 h v ( x ) > 1 in ( 0 , x ) and R 0 v h ( x ) R 0 h v ( x ) < 1 in ( x , L ) . Note that ( ρ 1 1 , ρ 3 1 ) satisfies

(3.50) d 1 ρ 1 x x 1 c 1 ρ 1 x 1 + λ ( x ) ρ 1 1 = g 1 ( x ) ρ 3 1 , x ( 0 , L ) , d 2 ρ 3 x x 1 c 2 ρ 3 x 1 + μ ( x ) V ρ 3 1 = g 2 ( x ) ρ 1 1 , x ( 0 , L ) , ρ 1 x 1 ( 0 ) = ρ 1 x 1 ( L ) = ρ 3 x 1 ( 0 ) = ρ 3 x 1 ( L ) = 0 .

By a e σ x trick, we obtain

d 1 e c 1 d 1 x ρ 1 x 1 x d 2 e c 2 d 2 x ρ 3 x 1 x = e σ x λ ( x ) g 1 ( x ) g 2 ( x ) μ ( x ) V ρ 1 1 ρ 3 1 = J ( x ) ρ 1 1 ρ 3 1 .

Since ( ρ 1 1 , ρ 3 1 ) = k ( x ) ( e J 1 , e J 2 ) and J ( x ) ( e J 1 , e J 2 ) T = k J ( x ) ( e J 1 , e J 2 ) T , it follows that

d 1 e c 1 d 1 x ρ 1 x 1 x d 2 e c 2 d 2 x ρ 3 x 1 x = k ( x ) k J ( x ) e J 1 e J 2 = k J ( x ) ρ 1 1 ρ 3 1 .

Accordingly, k J ( x ) > 0 in ( 0 , x ) and k J ( x ) < 0 in ( x , L ) . Hence,

e c 1 d 1 x ρ 1 x 1 x < 0 , x ( 0 , x ) , > 0 , x ( x , L ) ,

and

e c 2 d 2 x ρ 3 x 1 x < 0 , x ( 0 , x ) , > 0 , x ( x , L ) ,

which implies that e c 1 d 1 x ρ 1 x 1 and e c 2 d 2 x ρ 3 x 1 monotonically decrease on x ( 0 , x ) and increase on ( x , L ) . Thanks to ρ j x 1 ( 0 ) = ρ j x 1 ( L ) = 0 , j = 1 , 3 , we obtain e c 2 d 2 x ρ 3 x 1 < 0 and e c 1 d 1 x ρ 1 x 1 < 0 in ( 0 , L ) , and thereby, ρ j x 1 < 0 in ( 0 , L ) , j = 1 , 3 . This proves (i).

The proof of (ii) resembles that of (i), so we omit the specifics. This proves Lemma 2.3.

3.5.2 Proof of Theorem 2.8

Fixed d 1 > 0 , d 2 > 0 and c 2 > 0 . Differentiating problem (3.8) w.r.t. c 1 gives

(3.51) d 1 ρ 1 x x ρ 1 x c 1 ρ 1 x + λ ( x ) ρ 1 = R 0 R 0 2 g 1 ( x ) ρ 3 + 1 R 0 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x c 2 ρ 3 x + μ ( x ) V ρ 3 = R 0 R 0 2 g 2 ( x ) ρ 1 + 1 R 0 g 2 ( x ) ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) = 0 ,

where represents the derivative of c 1 . We multiply the ρ 1 -equation of (3.51) by e c 1 d 1 x ρ 1 and the ρ 1 -equation of (3.8) by e c 1 d 1 x ρ 1 , respectively, then integrate them on ( 0 , L ) , obtaining that

d 1 0 L e c 1 d 1 x ρ 1 x ρ 1 x d x + 0 L e c 1 d 1 x λ ( x ) ρ 1 ρ 1 d x = 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x , d 1 0 L e c 1 d 1 x ρ 1 x ρ 1 x d x 0 L e c 1 d 1 x ρ 1 ρ 1 x d x + 0 L e c 1 d 1 x λ ( x ) ρ 1 ρ 1 d x = R 0 R 0 2 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x + 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x .

Subtracting the aforementioned two equations yields

(3.52) R 0 R 0 2 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x = 0 L e c 1 d 1 x ρ 1 ρ 1 x d x + 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ( ρ 1 ρ 3 ρ 1 ρ 3 ) d x .

Similarly, we deal with the ρ 3 -equation of (3.8) and ρ 3 -equation of (3.51), obtaining that

d 2 0 L e c 2 d 2 x ρ 3 x ρ 3 x d x + 0 L e c 2 d 2 x μ ( x ) V ρ 3 ρ 3 d x = 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x , d 2 0 L e c 2 d 2 x ρ 3 x ρ 3 x d x + 0 L e c 2 d 2 x μ ( x ) V ρ 3 ρ 3 d x = R 0 R 0 2 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x + 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x .

As a result,

(3.53) R 0 R 0 2 0 L e c 2 d 2 x g 2 ( x ) ρ 1 ρ 3 d x = 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ( ρ 1 ρ 3 ρ 1 ρ 3 ) d x .

Adding (3.52) and (3.53) and according to the assumption (A1), and g 1 ( x ) g 2 ( x ) into ( 0 , L ) , we then have

(3.54) R 0 R 0 2 0 L e σ x ( g 1 ( x ) + g 2 ( x ) ) ρ 1 ρ 3 d x = 0 L e σ x ρ 1 ρ 1 x d x .

By Theorem 2.7, (A1), and (H1), we directly have

lim c 1 R 0 = lim c 1 , c 2 R 0 = R 0 loc ( L ) < 1 .

Thanks to Theorems 2.6 and 2.7, we obtain

lim c 1 0 R 0 = lim c 1 0 , c 2 0 R 0 = R ˜ 0 > 1 .

As a consequence, we can find at least a c 1 = c 1 ( d 1 , d 2 ) > 0 such that R 0 ( d 1 , d 2 , c 1 , c 2 ) = 1 . Relying on (3.54) and Lemma 2.3, we know that

R 0 ( d 1 , d 2 , c 1 , c 2 ) R 0 2 ( d 1 , d 2 , c 1 , c 2 ) 0 L e c 1 d 1 x ( g 1 ( x ) + g 2 ( x ) ) ρ 1 ρ 3 d x = 0 L e c 1 d 1 x ρ 1 ρ 1 x d x < 0 .

Due to g 1 ( x ) > 0 , g 2 ( x ) > 0 , and ( ρ 1 , ρ 3 ) > 0 , we know that R 0 ( d 1 , d 2 , c 1 , c 2 ) < 0 , i.e., c 1 is unique. Hence, R 0 ( d 1 , d 2 , c 1 , c 2 ) > 1 when 0 < c 1 < c 1 and R 0 ( d 1 , d 2 , c 1 , c 2 ) < 1 when c 1 > c 1 . The proof of the conclusion on c 2 is similar, and so we skip the details here.

Arguing by contradiction, if there exist 0 < q 0 and 0 < q 1 such that Γ 1 ( d 1 , d 2 ) q 0 and Γ 2 ( d 1 , d 2 ) q 1 as d 1 0 and d 2 0 , then by Theorem 2.7 and (H1), we obtain

lim Γ 1 ( d 1 , d 2 ) q 0 , Γ 1 ( d 1 , d 2 ) d 1 Γ 2 ( d 1 , d 2 ) q 1 , Γ 2 ( d 1 , d 2 ) d 2 R 0 ( d 1 , d 2 , Γ 1 ( d 1 , d 2 ) , Γ 2 ( d 1 , d 2 ) ) = R 0 loc ( L ) < 1 ,

which contradicts with R 0 ( d 1 , d 2 , Γ 1 ( d 1 , d 2 ) , Γ 2 ( d 1 , d 2 ) ) = 1 . As a result, Γ i ( d 1 , d 2 ) 0 ( i = 1 , 2 ) when d 1 0 and d 2 0 .

Similarly, if Γ 1 ( d 1 , d 2 ) d 1 and Γ 2 ( d 1 , d 2 ) d 2 as d 1 and d 2 , then a contradiction occurs. Thus, for sufficiently large d 1 , d 2 , Γ 1 ( d 1 , d 2 ) d 1 and Γ 2 ( d 1 , d 2 ) d 2 are bounded, which allow us to assume that Γ 1 ( d 1 , d 2 ) d 1 Θ ˆ 1 and Γ 2 ( d 1 , d 2 ) d 2 Θ ˆ 1 for constant Θ ˆ 1 0 , as d 1 and d 2 . Corresponding to R 0 ( d 1 , d 2 , Γ 1 ( d 1 , d 2 ) , Γ 2 ( d 1 , d 2 ) ) = 1 of (3.8), let ( ρ ¯ 1 , ρ ¯ 3 ) be the positive eigenfunction, satisfying ρ ¯ 1 + ρ ¯ 3 = 1 . Let us multiply e Γ 1 ( d 1 , d 2 ) d 1 x and e Γ 2 ( d 1 , d 2 ) d 2 x onto the two equations of (3.8), respectively, obtaining that

(3.55) d 1 ( e Γ 1 ( d 1 , d 2 ) d 1 x ρ ¯ 1 x ) x = e Γ 1 ( d 1 , d 2 ) d 1 x [ λ ( x ) ρ ¯ 1 + g 1 ( x ) ρ ¯ 3 ] , x ( 0 , L ) , d 2 ( e Γ 2 ( d 1 , d 2 ) d 2 x ρ ¯ 3 x ) x = e Γ 2 ( d 1 , d 2 ) d 2 x [ μ ( x ) V ρ ¯ 3 + g 2 ( x ) ρ ¯ 1 ] , x ( 0 , L ) , ρ ¯ 1 x ( 0 ) = ρ ¯ 1 x ( L ) = ρ ¯ 3 x ( 0 ) = ρ ¯ 3 x ( L ) = 0 .

Integrating (3.55) over ( 0 , L ) gives that

(3.56) 0 L e Γ 1 ( d 1 , d 2 ) d 1 x λ ( x ) ρ ¯ 1 d x + 0 L e Γ 1 ( d 1 , d 2 ) d 1 x g 1 ( x ) ρ ¯ 3 d x = 0 , x ( 0 , L ) , 0 L e Γ 2 ( d 1 , d 2 ) d 2 x μ ( x ) V ρ ¯ 3 d x + 0 L e Γ 2 ( d 1 , d 2 ) d 2 x g 2 ( x ) ρ ¯ 1 d x = 0 , x ( 0 , L ) .

With the help of Theorem 2.7 and the elliptic regularity estimate, there exist ρ ˜ 1 > 0 and ρ ˜ 3 > 0 such that ( ρ ¯ 1 , ρ ¯ 3 ) ( ρ ˜ 1 , ρ ˜ 3 ) as d 1 and d 2 . Passing to the limit d 1 and d 2 in (3.56) gives

0 L e Θ ˆ 1 x λ ( x ) d x 0 L e Θ ˆ 1 x g 1 ( x ) d x 0 L e Θ ˆ 1 x g 2 ( x ) d x 0 L e Θ ˆ 1 x μ ( x ) V d x ρ ˜ 1 ρ ˜ 3 = N ρ ˜ 1 ρ ˜ 3 = 0 .

Since ρ ˜ 1 > 0 and ρ ˜ 3 > 0 , the matrix N must be a singular matrix, i.e.,

N = 0 L e Θ ˆ 1 x λ ( x ) d x 0 L e Θ ˆ 1 x μ ( x ) V ¯ d x 0 L e Θ ˆ 1 x g 1 ( x ) d x 0 L e Θ ˆ 1 x g 2 ( x ) d x = 0 .

Recall that H ( Θ ) has been defined in Theorem 2.8. The existence of Θ ˆ 1 can be proved by a similar argument as in [31, Lemma 4.2]. This completes the proof of Theorem 2.8.

3.5.3 Proof of Theorem 2.9

Theorem 2.9 will be achieved through proving the following two lemmas.

Lemma 3.4

Under the conditions of Lemma 2.3, assume that (A1)–(A2) hold. If R 0 a < 1 and g 1 ( x ) g 2 ( x ) , x ( 0 , L ) , then R ˜ 0 ( d ˜ 1 , d ˜ 2 ) = 1 admits a unique positive root ( d ˜ 1 , d ˜ 2 ) . Furthermore, we have the following conclusions:

  1. In the case of (H1), then

    1. When ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) , we can find unique points c ˜ 1 = c ˜ 1 ( d 1 , d 2 ) and c ˜ 2 = c ˜ 2 ( d 1 , d 2 ) such that R 0 ( d 1 , d 2 , c 1 , c 2 ) > 1 as c 1 < c ˜ 1 or c 2 < c ˜ 2 , and R 0 ( d 1 , d 2 , c 1 , c 2 ) < 1 as c 1 > c ˜ 1 or c 2 > c ˜ 2 ;

    2. When ( d 1 , d 2 ) [ d ˜ 1 , ) × [ d ˜ 2 , ) , R 0 ( d 1 , d 2 , c 1 , c 2 ) < 1 .

  2. In the case of (H2), then

    1. When ( d 1 , d 2 ) ( 0 , d ˜ 1 ] × ( 0 , d ˜ 2 ] , R 0 ( d 1 , d 2 , c 1 , c 2 ) > 1 ;

    2. When ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) , we can find unique points c ˆ 1 = c ˆ 1 ( d 1 , d 2 ) and c ˆ 2 = c ˆ 2 ( d 1 , d 2 ) such that R 0 ( d 1 , d 2 , c 1 , c 2 ) < 1 as c 1 < c ˆ 1 or c 2 < c ˆ 2 , and R 0 ( d 1 , d 2 , c 1 , c 2 ) > 1 as c 1 > c ˆ 1 or c 2 > c ˆ 2 .

Proof

We only prove (i), since (ii) can be similarly achieved. Based on the proof of Theorem 2.8 and (ii) of Theorem 2.6, if R 0 ( d 1 , d 2 , c ˜ i ) = 1 , it means that c ˜ i exists. Furthermore, from R 0 c ˜ i < 0 , we can see that c ˜ i is unique, which suggests that (i-1) is valid. For ( d 1 , d 2 ) [ d ˜ 1 , ) × [ d ˜ 2 , ) , it follows from (ii) of Theorem 2.6 that

lim c 1 0 , c 2 0 R 0 ( c 1 , c 2 ) = R ˜ 0 1 and lim c 1 , c 2 R 0 ( c 1 , c 2 ) = R 0 loc ( L ) < 1 .

Obviously, we cannot find c i , i = 1 , 2 , such that R 0 ( d 1 , d 2 , c i ) = 1 . Hence, the assertion in (i-2) holds. This completes the proof.□

Remark 3.2

In the forthcoming discussions, we will demonstrate that c i = c ˜ i = 0 . Specifically, Lemma 3.4 shows that if R 0 loc ( L ) < 1 , then R ˜ 0 ( d ˜ 1 , d ˜ 2 , c i ) < 1 for each c i > c ˜ i ( d ˜ 1 , d ˜ 2 ) = 0 , and if R 0 loc ( L ) > 1 , then R ˜ 0 ( d ˜ 1 , d ˜ 2 , c i ) > 1 for each c i > c ˜ i ( d ˜ 1 , d ˜ 2 ) = 0 , i = 1 , 2 .

Lemma 3.5

Under the conditions of Lemma 3.4, assume that (A1)–(A2) hold. If R 0 a < 1 and g 1 ( x ) g 2 ( x ) , x ( 0 , L ) , then R ˜ 0 ( d ˜ 1 , d ˜ 2 ) = 1 admits a unique positive root ( d ˜ 1 , d ˜ 2 ) . Furthermore, we have the following conclusions:

  1. In the case of (H1), there exists function Γ i ( d 1 , d 2 ) : ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) ( 0 , ) , i = 3 , 4 , such that R 0 ( d 1 , d 2 , Γ i ( d 1 , d 2 ) ) = 1 . In addition, Γ i ( d 1 , d 2 ) satisfies

    lim d 1 0 , d 2 0 Γ i ( d 1 , d 2 ) = 0 a n d lim d 1 d ˜ 1 , d 2 d ˜ 2 Γ i ( d 1 , d 2 ) = 0 ;

  2. In the case of (H2), there exists function Γ j ( d 1 , d 2 ) : ( d ˜ 1 , ) × ( d ˜ 2 , ) ( 0 , ) , j = 5 , 6 , such that R 0 ( d 1 , d 2 , Γ j ( d 1 , d 2 ) ) = 1 . Furthermore, Γ 5 ( d 1 , d 2 ) and Γ 6 ( d 1 , d 2 ) increase monotonically w.r.t. d 1 and d 2 , respectively, and satisfies

    lim d 1 d ˜ 1 + , d 2 d ˜ 2 + Γ j ( d 1 , d 2 ) = 0 , lim d 1 , d 2 Γ 5 ( d 1 , d 2 ) d 1 = Θ 2 , and lim d 1 , d 2 Γ 6 ( d 1 , d 2 ) d 2 = Θ 2 ,

    where Θ 2 is the positive solution of H ( Θ ) = 0 .

Proof

Based on Lemma 3.4, the existence of Γ i ( i = 3 , 4 , 5 , 6 ) is obvious. We shall prove (i) indirectly, and suppose that there are r 3 > 0 and r 4 > 0 such that ( Γ 3 ( d 1 , d 2 ) , Γ 4 ( d 1 , d 2 ) ) ( r 3 , r 4 ) as d 1 0 and d 2 0 . It is then observed from Theorem 2.7 that

lim d 1 0 + , d 2 0 + Γ 3 ( d 1 , d 2 ) r 3 , Γ 4 ( d 1 , d 2 ) r 4 R 0 ( d 1 , d 2 , Γ 3 ( d 1 , d 2 ) , Γ 4 ( d 1 , d 2 ) ) = R 0 loc ( L ) < 1 ,

which is a contradiction, since R 0 ( d 1 , d 2 , Γ 3 , Γ 4 ) = 1 . Thus, r 3 = r 4 = 0 .

To deal with Γ i ( d 1 , d 2 ) 0 ( i = 3 , 4 ) as d 1 d ˜ 1 and d 2 d ˜ 2 , assume that there exist r ¯ 3 > 0 and r ¯ 4 > 0 such that Γ 3 ( d 1 , d 2 ) r ¯ 3 and Γ 4 ( d 1 , d 2 ) r ¯ 4 as d 1 d ˜ 1 and d 2 d ˜ 2 . By (3.8), there exists ( ρ 1 r ¯ 3 , ρ 3 r ¯ 4 ) fulfilling that

(3.57) d ˜ 1 ( ρ 1 r ¯ 3 ) x x r ¯ 3 ( ρ 1 r ¯ 3 ) x + λ ( x ) ρ 1 r ¯ 3 = g 1 ( x ) ρ 3 r ¯ 4 , x ( 0 , L ) , d ˜ 2 ( ρ 3 r ¯ 4 ) x x r ¯ 4 ( ρ 3 r ¯ 4 ) x + μ ( x ) V ρ 3 r ¯ 4 = g 2 ( x ) ρ 1 r ¯ 3 , x ( 0 , L ) , ( ρ 1 r ¯ 3 ) x ( 0 ) = ( ρ 1 r ¯ 3 ) x ( L ) = ( ρ 3 r ¯ 4 ) x ( 0 ) = ( ρ 3 r ¯ 4 ) x ( L ) .

As ( d ˜ 1 , d ˜ 2 ) is the unique root of R ˜ 0 ( d 1 , d 2 ) = 1 , there is a positive function ( ρ ˜ 1 r ¯ 3 , ρ ˜ 3 r ¯ 4 ) satisfying

(3.58) d ˜ 1 ( ρ ˜ 1 r ¯ 3 ) x x + λ ( x ) ρ ˜ 1 r ¯ 3 = g 1 ( x ) ρ ˜ 3 r ¯ 4 , x ( 0 , L ) , d ˜ 2 ( ρ ˜ 3 r ¯ 4 ) x x + μ ( x ) V ρ ˜ 3 r ¯ 4 = g 2 ( x ) ρ ˜ 1 r ¯ 3 , x ( 0 , L ) , ( ρ ˜ 1 r ¯ 3 ) x ( 0 ) = ( ρ ˜ 1 r ¯ 3 ) x ( L ) = ( ρ ˜ 3 r ¯ 4 ) x ( 0 ) = ( ρ ˜ 3 r ¯ 4 ) x ( L ) .

Let us multiply ρ ˜ 1 r ¯ 3 and ρ ˜ 3 r ¯ 4 onto the two equations of (3.57) and then integrate, obtaining that

(3.59) d ˜ 1 0 L ( ρ 1 r ¯ 3 ) x ( ρ ˜ 1 r ¯ 3 ) x d x r ¯ 3 0 L ρ ˜ 1 r ¯ 3 ( ρ 1 r ¯ 3 ) x d x + 0 L λ ( x ) ρ 1 r ¯ 3 ρ ˜ 1 r ¯ 3 d x = 0 L g 1 ( x ) ρ 3 r ¯ 4 ρ ˜ 1 r ¯ 3 d x , d ˜ 2 0 L ( ρ 3 r ¯ 4 ) x ( ρ ˜ 2 r ¯ 4 ) x d x r ¯ 4 0 L ρ ˜ 3 r ¯ 4 ( ρ 3 r ¯ 4 ) x d x + 0 L μ ( x ) V ρ 3 r ¯ 4 ρ ˜ 3 r ¯ 4 d x = 0 L g 2 ( x ) ρ 1 r ¯ 3 ρ ˜ 3 r ¯ 4 d x .

Similarly, relying on the ρ 1 r ¯ 3 and ρ 3 r ¯ 4 trick onto (3.58), we can obtain

(3.60) d ˜ 1 0 L ( ρ 1 r ¯ 3 ) x ( ρ ˜ 1 r ¯ 3 ) x d x + 0 L λ ( x ) ρ 1 r ¯ 3 ρ ˜ 1 r ¯ 3 d x = 0 L g 1 ( x ) ρ ˜ 3 r ¯ 4 ρ 1 r ¯ 3 d x , d ˜ 2 0 L ( ρ 3 r ¯ 4 ) x ( ρ ˜ 2 r ¯ 4 ) x d x + 0 L μ ( x ) V ρ 3 r ¯ 4 ρ ˜ 3 r ¯ 4 d x = 0 L g 2 ( x ) ρ ˜ 1 r ¯ 3 ρ 3 r ¯ 4 d x .

From (3.59) and (3.60), we then have

r ¯ 3 0 L ρ ˜ 1 r ¯ 3 ( ρ 1 r ¯ 3 ) x d x r ¯ 4 0 L ρ ˜ 3 r ¯ 4 ( ρ 3 r ¯ 4 ) x d x = 0 L [ g 1 ( x ) g 2 ( x ) ] ( ρ 3 r ¯ 4 ρ ˜ 1 r ¯ 3 ρ ˜ 3 r ¯ 4 ρ 1 r ¯ 3 ) d x = 0 ,

owing to g 1 ( x ) g 2 ( x ) for x ( 0 , L ) . Furthermore, from ( ρ 1 r ¯ 3 ) x < 0 and ( ρ 3 r ¯ 4 ) x < 0 as stated in (i) of Lemma 2.3, we then have r ¯ 3 = r ¯ 4 = 0 . This proves (i).

To proceed to prove (ii), we claim that R 0 d 1 < 0 and R 0 d 2 < 0 if d 1 and d 2 satisfy R 0 ( d 1 , d 2 ) = 1 . In fact, differentiating (3.8) w.r.t. d 1 yields that

(3.61) ρ 1 x x d 1 ρ 1 x x c 1 ρ 1 x + λ ( x ) ρ 1 = R 0 R 0 2 g 1 ( x ) ρ 3 + 1 R 0 g 1 ( x ) ρ 3 , x ( 0 , L ) , d 2 ρ 3 x x c 2 ρ 3 x + μ ( x ) V ρ 3 = R 0 R 0 2 g 2 ( x ) ρ 1 + 1 R 0 g 2 ( x ) ρ 1 , x ( 0 , L ) , ρ 1 x ( 0 ) = ρ 1 x ( L ) = ρ 3 x ( 0 ) = ρ 3 x ( L ) .

Applying the e c 1 d 1 x ρ 1 and e c 2 d 2 x ρ 3 trick onto the two equations of (3.8), we obtain

(3.62) d 1 0 L e c 1 d 1 x ρ 1 x ρ 1 x d x + 0 L e c 1 d 1 x λ ( x ) ρ 1 ρ 1 d x = 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x , d 2 0 L e c 2 d 2 x ρ 3 x ρ 3 x d x + 0 L e c 2 d 2 x μ ( x ) V ρ 3 ρ 3 d x = 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x .

Similarly, relying on the e c 1 d 1 x ρ 1 and e c 2 d 2 x ρ 3 trick onto (3.61), we obtain

(3.63) c 1 d 1 0 L e c 1 d 1 x ρ 1 ρ 1 x d x + 0 L e c 1 d 1 x ρ 1 x 2 d x + d 1 0 L e c 1 d 1 x ρ 1 x ρ 1 x d x + 0 L e c 1 d 1 x λ ( x ) ρ 1 ρ 1 d x = R 0 R 0 2 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x + 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x , d 2 0 L e c 2 d 2 x ρ 3 x ρ 3 x d x + 0 L e c 2 d 2 x μ ( x ) V ρ 3 ρ 3 d x = R 0 R 0 2 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x + 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x .

Subtracting the two equations of (3.62) and (3.63), we obtain

R 0 R 0 2 0 L e c 1 d 1 x g 1 ( x ) ρ 1 ρ 3 d x = 0 L e c 1 d 1 x ρ 1 x 2 d x c 1 d 1 0 L e c 1 d 1 x ρ 1 ρ 1 x d x + 1 R 0 0 L e c 1 d 1 x g 1 ( x ) ( ρ 1 ρ 3 ρ 1 ρ 3 ) d x , R 0 R 0 2 0 L e c 2 d 2 x g 2 ( x ) ρ 3 ρ 1 d x = 1 R 0 0 L e c 2 d 2 x g 2 ( x ) ( ρ 3 ρ 1 ρ 3 ρ 1 ) d x .

According to the assumption (A1) and g 1 ( x ) g 2 ( x ) in ( 0 , L ) , it follows that

R 0 R 0 2 0 L e c 1 d 1 x [ g 1 ( x ) + g 2 ( x ) ] ρ 1 ρ 3 d x = 0 L e c 1 d 1 x ρ 1 x 2 d x c 1 d 1 0 L e c 1 d 1 x ρ 1 ρ 1 x d x .

By (ii) of Lemma 2.3, we obtain R 0 < 0 . Similarly, one can prove that R 0 d 2 < 0 when R 0 ( d 1 , d 2 ) = 1 .

By differentiating the equation R 0 ( d 1 , d 2 , Γ 5 ( d 1 , d 2 ) , Γ 6 ( d 1 , d 2 ) ) = 1 w.r.t. d 1 , we know that

R 0 d 1 + R 0 c 1 Γ 5 ( d 1 , d 2 ) d 1 + R 0 c 2 Γ 6 ( d 1 , d 2 ) d 1 = 0 .

Recall that Γ 6 ( d 1 , d 2 ) = Γ 5 ( d 1 , d 2 ) d 2 d 1 . Then, differentiating it w.r.t. d 1 gives

Γ 6 ( d 1 , d 2 ) d 1 = d 2 d 1 2 Γ 5 ( d 1 , d 2 ) + d 2 d 1 Γ 5 ( d 1 , d 2 ) d 1 .

Thus,

Γ 5 ( d 1 , d 2 ) d 1 R 0 c 1 + d 2 d 1 R 0 c 2 = d 2 d 1 2 Γ 5 ( d 1 , d 2 ) R 0 c 2 R 0 d 1 .

Since R 0 d 1 < 0 from the aforementioned claim and R 0 c i > 0 ( i = 1 , 2 ) in (ii-2) of Lemma 3.4, it can be summarized that Γ 5 ( d 1 , d 2 ) d 1 > 0 , which indicates that Γ 5 ( d 1 , d 2 ) increase w.r.t. d 1 . Similarly, Γ 6 ( d 1 , d 2 ) increase w.r.t. d 2 .

Like in the proof of (i) and Theorem 2.8, let Θ 2 be the positive solution of H ( Θ ) = 0 , we then have

lim d 1 d ˜ 1 + , d 2 d ˜ 2 + Γ j ( d 1 , d 2 ) = 0 , j = 5 , 6 , lim d 1 , d 2 Γ 5 ( d 1 , d 2 ) d 1 = Θ 2 , and lim d 1 , d 2 Γ 6 ( d 1 , d 2 ) d 2 = Θ 2 .

This completes the proof.□

Theorem 2.9 is a direct consequence of aforementioned lemmas.

3.6 Aggregation phenomenon of EE: Proof of Theorems 2.10 and 2.11

To prove Theorems 2.10 and 2.11, we shall appeal to the following lemmas.

Lemma 3.6

For i = 1 , 2 , let h i ( ) > 0 and h i ( ) , r i ( ) C ( [ 0 , L ] ) . If ( n 1 , n 2 ) is a solution of

(3.64) d 1 n 1 x x c 1 n 1 x + h 1 ( x ) n 2 r 1 ( x ) n 1 0 , x ( 0 , L ) , d 2 n 2 x x c 2 n 2 x + h 2 ( x ) n 1 r 2 ( x ) n 2 0 , x ( 0 , L ) , d 1 n 1 x ( 0 ) + c 1 n 1 ( 0 ) 0 , n 1 ( L ) 0 , d 2 n 2 x ( 0 ) + c 2 n 2 ( 0 ) 0 , n 2 ( L ) 0 ,

c 1 d 1 = c 2 d 2 and c i 2 d i 4 r i + , then n i ( x ) 0 or n i ( x ) > 0 , x [ 0 , L ) .

Proof

Let ( n 1 , n 2 ) = e ς 2 x ( n ˜ 1 , n ˜ 2 ) , where ς = c 1 d 1 = c 2 d 2 . Then, ( n ˜ 1 , n ˜ 2 ) satisfies

(3.65) d 1 x 2 c 1 2 2 d 1 n ˜ 1 + h 1 ( x ) n ˜ 2 + c 1 2 4 d 1 r 1 ( x ) n ˜ 1 0 , x ( 0 , L ) , d 2 x 2 c 2 2 2 d 2 n ˜ 2 + h 2 ( x ) n ˜ 1 + c 2 2 4 d 2 r 2 ( x ) n ˜ 2 0 , x ( 0 , L ) , d 1 n ˜ 1 x ( 0 ) + c 1 2 n ˜ 1 ( 0 ) 0 , n ˜ 1 ( L ) 0 , d 2 n ˜ 2 x ( 0 ) + c 2 2 n ˜ 2 ( 0 ) 0 , n ˜ 2 ( L ) 0 ,

which is cooperative. With the aid of strong maximum principle (see, e.g., [25, Lemma 2.4] and [34, Lemma 2.1.2]), we know that n ˜ i ( x ) 0 or n ˜ i ( x ) > 0 , i = 1 , 2 , x [ 0 , L ) . Hence, the assertion on n i ( x ) , i = 1 , 2 , directly follows. This proves Lemma 3.6.□

The following result gives the sub- and super-solutions of system (2.1).

Lemma 3.7

Suppose that (A1) holds, and c 1 2 d 1 > ( ν 1 ) 2 and c 2 2 d 2 > ( ν 2 ) 2 , where ν 1 = λ + + ( a β 1 ) + + ν 1 0 + 2 and ν 2 = ( μ V ) + + ( b β 2 p V l H u ) + + ν 2 0 + 2 , and ν 1 0 and ν 2 0 are the positive constants such that ν 1 c 1 = ν 2 c 2 . Then,

H ̲ i H i ( x ) H ¯ i , and V ̲ i V i ( x ) V ¯ i , x [ 0 , L ] ,

with

( H ̲ i , H ¯ i ) = H i ( L ) e c 1 d 1 + ν 1 c 1 ( L x ) , K 5 e c 1 d 1 ν 1 c 1 ( L x ) ,

and

( V ̲ i , V ¯ i ) = ( V i ( L ) e c 2 d 2 + ν 2 c 2 ( L x ) , K 5 e c 2 d 2 ν 2 c 2 ( L x ) ) ,

where K 5 = max { H i ( L ) , V i ( L ) } .

Proof

By simple calculations, we obtain

d 1 H ¯ i x x c 1 H ¯ i x + a β 1 ( x ) l H u ( x ) p H i + l H u V ¯ i λ ( x ) H ¯ i = d 1 c 1 d 1 ν 1 c 1 2 H ¯ i c 1 c 1 d 1 ν 1 c 1 H ¯ i λ ( x ) H ¯ i + a β 1 ( x ) l H u ( x ) p H i + l H u V ¯ i ν 1 + d 1 ( ν 1 ) 2 c 1 2 λ ( x ) H ¯ i + a β 1 ( x ) V ¯ i ν 1 + d 1 ( ν 1 ) 2 c 1 2 H ¯ i + a β 1 ( x ) V ¯ i = ν 1 + d 1 ( ν 1 ) 2 c 1 2 K 5 e c 1 d 1 ν 1 c 1 ( L x ) + a β 1 ( x ) K 5 e c 2 d 2 ν 2 c 2 ( L x ) = ν 1 + d 1 ( ν 1 ) 2 c 1 2 + a β 1 ( x ) K 5 e c 1 d 1 ν 1 c 1 ( L x ) 1 + d 1 ( ν 1 ) 2 c 1 2 K 5 e c 1 d 1 ν 1 c 1 ( L x ) 0 ,

d 2 V ¯ i x x c 2 V ¯ i x + b β 2 ( x ) p V u p H i + l H u H ¯ i μ ( x ) ( V u + V i ) V ¯ i [ 1 + d 2 ( ν 2 ) 2 c 2 2 ] K 5 e c 2 d 2 ν 2 c 2 ( L x ) 0

and

d 1 H ¯ i x ( 0 ) + c 1 H ¯ i ( 0 ) = d 1 c 1 d 1 ν 1 c 1 H ¯ i ( 0 ) + c 1 H ¯ i ( 0 ) = d 1 ν 1 c 1 2 H ¯ i ( 0 ) 0 , H ¯ i ( L ) = K 5 , d 2 V ¯ 2 x ( 0 ) + c 2 V ¯ 2 ( 0 ) = d 2 c 2 d 2 ν 2 c 2 V ¯ 2 ( 0 ) + c 2 V ¯ 2 ( 0 ) = d 2 ν 2 c 2 2 V ¯ i ( 0 ) 0 , V ¯ i ( L ) = K 5 .

Setting n 1 = H ¯ i H i and n 2 = V ¯ i V i , we have

d 1 n 1 x x c 1 n 1 x λ ( x ) n 1 + a β 1 ( x ) l H u ( x ) n 2 p H i + l H u ( x ) = d 1 ( H ¯ i H i ) x x c 1 ( H ¯ i H i ) x λ ( x ) ( H ¯ i H i ) + a β 1 ( x ) l H u ( x ) ( V ¯ i V i ) p H i + l H u ( x ) = d 1 H ¯ i x x c 1 H ¯ i x + a β 1 ( x ) l H u ( x ) p H i + l H u V ¯ i λ ( x ) H ¯ i d 1 H i x x c 1 H i x + a β 1 ( x ) l H u ( x ) p H i + l H u V i λ ( x ) H i = d 1 H ¯ i x x c 1 H ¯ i x + a β 1 ( x ) l H u ( x ) p H i + l H u V ¯ i λ ( x ) H ¯ i 0 ,

d 2 n 2 x x c 2 n 2 x + b β 2 ( x ) p V u n 1 p H i + l H u μ ( x ) ( V u + V i ) n 2 0

and

d 1 n 1 x ( 0 ) + c 1 n 1 ( 0 ) = d 1 H ¯ i x ( 0 ) + c 1 H ¯ i ( 0 ) = d 1 ν 1 c 1 2 H ¯ i ( 0 ) 0 , n 1 ( L ) = H ¯ i ( L ) H i ( L ) = K 5 H i ( L ) 0 , d 2 n 2 x ( 0 ) + c 2 n 2 ( 0 ) = d 2 V ¯ i x ( 0 ) + c 2 V ¯ i ( 0 ) = d 1 ν 2 c 2 2 V ¯ i ( 0 ) 0 , n 2 ( L ) = V ¯ i ( L ) V i ( L ) = K 5 V i ( L ) 0 .

Based on Lemma 3.6, we see that for any given x [ 0 , L ) , n i ( x ) 0 , i = 1 , 2 , i.e., H i ( x ) H ¯ i ( x ) and V i ( x ) V ¯ i ( x ) . In a same fashion, H ̲ i ( x ) and V ̲ i ( x ) are sub-solutions of system (2.1), namely, H i ( x ) H ̲ i ( x ) and V i ( x ) V ̲ i ( x ) . This completes the proof.□

Lemma 3.8

For i = 1 , 2 , let ν i be defined in Lemma 3.7. Then, the functions

F 1 + ( ξ ) e ν 1 c 1 ξ 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ξ 1 , F 1 ( ξ ) e ν 1 c 1 ξ + 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ξ 1 ,

and

F 2 + ( ξ ) e ν 2 c 2 ξ 3 ν 2 d 2 c 2 2 e c 2 2 d 2 ξ 1 , F 2 ( ξ ) e ν 2 c 2 ξ + 3 ν 2 d 2 c 2 2 e c 2 2 d 2 ξ 1 , ξ [ 0 , L ] ,

satisfy F i + ( ξ ) 0 and F i ( ξ ) 0 , ξ [ 0 , L ] .

Proof

Direct calculation gives

F 1 + ( ξ ) = ν 1 c 1 e ν 1 c 1 ξ 3 ν 1 2 c 1 e c 1 2 d 1 ξ = ν 1 c 1 e ν 1 c 1 ξ 1 3 2 e c 1 2 d 1 ν 1 c 1 ξ ν 1 c 1 e ν 1 c 1 ξ 1 3 2 0 , ξ [ 0 , L ] ,

where denotes the derivative of ξ . Since F 1 + ( 0 ) < 0 , we have F 1 + ( ξ ) 0 , ξ [ 0 , L ] . Similarly, the assertions on F 1 , F 2 + , and F 2 hold. This proves Lemma 3.8.□

With Lemmas 3.63.8, we proceed to prove Theorems 2.10 and 2.11.

3.6.1 Proof of Theorem 2.10

By Theorem 2.2 and Lemma 3.2, (2.1) admits at least one EE. For the case that H i ( L ) > V i ( L ) , we then from Lemma 3.7 that K 5 = H i ( L ) and

H i ( L ) e c 1 d 1 + ν 1 c 1 ( L x ) H i ( x ) H i ( L ) e c 1 d 1 ν 1 c 1 ( L x ) , x [ 0 , L ] .

Relying on H i ( L ) e c 1 d 1 ( L x ) , we then have

(3.66) e c 1 d 1 ( L x ) e ν 1 c 1 ( L x ) 1 H i ( L ) H i ( x ) H i ( L ) e c 1 d 1 ( L x ) [ e ν 1 c 1 ( L x ) 1 ] e c 1 d 1 ( L x ) H i ( L ) .

According to Lemma 3.8, letting ξ = L x , then

F 1 + ( L x ) = e ν 1 c 1 ( L x ) 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) 1 0

and

F 1 ( L x ) = e ν 1 c 1 ( L x ) + 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) 1 0 .

Hence, for x [ 0 , L ] ,

e ν 1 c 1 ( L x ) 1 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) , and e ν 1 c 1 ( L x ) 1 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) .

Substituting it into (3.66) yields

H i ( L ) 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) = H i ( L ) 3 ν 1 d 1 c 1 2 e c 1 d 1 ( L x ) e c 1 2 d 1 ( L x ) e ν 1 c 1 ( L x ) 1 e c 1 d 1 ( L x ) H i ( L ) H i ( x ) H i ( L ) e c 1 d 1 ( L x ) [ e ν 1 c 1 ( L x ) 1 ] e c 1 d 1 ( L x ) H i ( L ) 3 ν 1 d 1 c 1 2 e c 1 d 1 ( L x ) e c 1 2 d 1 ( L x ) H i ( L ) = H i ( L ) 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) .

Consequently, we have

H i ( x ) H i ( L ) e c 1 d 1 ( L x ) 3 ν 1 d 1 c 1 2 e c 1 2 d 1 ( L x ) .

Similarly, we can cope with (2.8) for the case that H i ( L ) < V i ( L ) . This proves Theorem 2.10.

3.6.2 Proof of Theorem 2.11

If H i ( L ) > V i ( L ) , then from Lemma 3.7 and ξ = c 1 d 1 ( L x ) , we can obtain that for ξ 0 , c 1 L d 1 ,

H i ( L ) e ( 1 + ν 1 d 1 c 1 2 ) ξ H i L d 1 c 1 ξ H i ( L ) e ( 1 ν 1 d 1 c 1 2 ) ξ .

Furthermore, if d 1 c 1 2 = o ( 1 ) small enough, we can obtain that for ξ 0 , c 1 L d 1 ,

H i ( L ) e ( 1 + o ( 1 ) ) ξ H i L d 1 c 1 ξ H i ( L ) e ( 1 o ( 1 ) ) ξ , ξ 0 , c 1 L d 1 .

It then follows that

H i ( L ) 0 c 1 L d 1 e ( 1 + o ( 1 ) ) ξ d ξ 0 c 1 L d 1 H i L d 1 c 1 ξ d ξ H i ( L ) 0 c 1 L d 1 e ( 1 o ( 1 ) ) ξ d ξ , ξ 0 , c 1 L d 1 .

Due to

0 c 1 L d 1 H i L d 1 c 1 ξ d ξ = c 1 d 1 0 L H i ( x ) d x ,

we obtain

lim c 1 d 1 , c 1 2 d 1 c 1 d 1 H i ( L ) 0 L H i ( x ) d x = 1 .

By applying the same arguments, the other scenarios can also be validated. This proves Theorem 2.11.

4 Discussion

We formulated and analyzed a vector-borne reaction–diffusion–advection model with vector-bias mechanism in a spatially heterogeneous environment. One of the significant features in our model is that we can consider the effects of advection and diffusion rate on the disease transmission, which poses new challenges to theoretical analysis. We obtained the threshold dynamics in terms of R 0 . Through the variational characterization of the BRN, we investigate its asymptotic profiles w.r.t. the diffusion rates and advection rates. Moreover, through classifying the level set of the R 0 , we analyzed the effects of advection and diffusion terms on the dynamics. Our main finding lies in when the influence of advection holds the dominant position, the infected individuals will be aggregated at the downstream end x = L .

We proved the boundedness of solution of system (2.1) by utilizing the comparison principle, [31, Theorem 2.1] and [21], addressing the well-posedness of the model (2.1) (see Theorem 2.1). In addition, the DFE E 0 is unstable and E 1 is g.a.s. when R 0 < 1 , and system (2.1) is UP-EE when R 0 > 1 . Compared with the existing result in [30], our results supplement the results of [30] in a non-advection homogeneous environment and reveals some new phenomena, such as the asymptotic profiles of R 0 with and without advection terms and the classification of level set of the R 0 . Moreover, we can see from Lemma 3.1 that R 0 will increase with p l , which implies that the effect of vector-bias has a great impact on the spread of disease. Specifically, not only the diffusion rate and advection rate have effects on the R 0 , but p l also has a great effect on it. In other words, the vector-borne disease infection risk would be underestimated if the vector-bias mechanism is ignored.

The level set of R 0 were classified with different cases, and some crucial conclusions were founded (Theorem 2.8 and 2.9).

  1. As shown in Theorem 2.8, there exist unique surfaces Γ 1 and Γ 2 , such that E 1 is g.a.s. for any c 1 > Γ 1 or c 2 > Γ 2 (namely, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 S L H or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 S L H ), and system (2.1) is UP-EE if c 1 < Γ 1 or c 2 < Γ 2 (specifically, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 U L H or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 U L H ), if R 0 a > 1 , and (H1) holds (Figure 2).

  2. As indicated in (i) of Theorem 2.9, there exist two constants d ˜ 1 and d ˜ 2 such that, as ( d 1 , d 2 ) ( 0 , d ˜ 1 ) × ( 0 , d ˜ 2 ) , there exist unique surfaces Γ 3 and Γ 4 , when c 1 > Γ 3 or c 2 > Γ 4 , E 1 is g.a.s. (namely, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 S L L 1 or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 S L L 1 ), and system (2.1) is UP-EE if c 1 < Γ 3 or c 2 < Γ 4 (specifically, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 U L L or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 U L L ); as ( d 1 , d 2 ) [ d ˜ 1 , ) × [ d ˜ 2 , ) , E 1 is g.a.s. (specifically, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 U L L or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 U L L ), if R 0 a < 1 , and (H1) holds (Figure 3).

  3. As indicated in (ii) of Theorem 2.9, there are two vital constants d ˜ 1 and d ˜ 2 such that, as ( d 1 , d 2 ) ( 0 , d ˜ 1 ] × ( 0 , d ˜ 2 ] , system (2.1) is UP-EE (specifically, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 U H L 2 or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 U H L 2 ); as ( d 1 , d 2 ) ( d ˜ 1 , ) × ( d ˜ 2 , ) , there exist unique surfaces Γ 5 and Γ 6 , when 0 < c 1 < Γ 5 or 0 < c 2 < Γ 6 , E 1 is g.a.s. (namely, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 S H L or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 S H L ), and system (2.1) is UP-EE for any c 1 > Γ 5 or c 2 > Γ 6 (specifically, ( d 1 , d 2 , c 1 ) located in region Ξ c 1 U H L 1 or ( d 1 , d 2 , c 2 ) located in region Ξ c 2 U H L 1 ), if R 0 a > 1 , and (H2) holds (Figure 4).

Finally, we analyzed the aggregation phenomenon of EE (Theorems 2.10 and 2.11). Theorems 2.10 and 2.11 indicated that under certain circumstances, if the advection rates are large relative to dispersal rates, the infected individuals will aggregate at downstream end.

Our findings complement the results of vector-borne disease in non-advective environments and may provide several new clues for the investigation and control of the disease. It should be pointed out that due to the complexity of model (2.1), some assumptions are harsh, just for mathematical purposes only. There are quite a few ways to improve our model. For example, we can consider the vector-borne disease model in the case that hosts can random walk without advective effects but vectors with, or consider the influence of periodic delay of vectors on the disease dynamics. We leave these questions for further investigations.

Acknowledgments

The authors would like to thank the referees and editor for many helpful comments. J. Wang was supported by the National Natural Science Foundation of China (Number 12071115 and 12471460), the Heilongjiang Natural Science Funds for Distinguished Young Scholar (Number JQ2023A005), and the Heilongjiang Provincial Key Laboratory of the Theory and Computation of Complex Systems, P. R. China.

  1. Author contributions: Jiaxing Liu: Writing-original draft, Methodology. Jinliang Wang: Writing-review & editing, Supervision, Methodology, Funding acquisition, Conceptualization.

  2. Conflict of interest: The authors declare that there is no conflict of interest regarding the publication of this article.

References

[1] L. J. S. Allen, B. M. Bolker, Y. Lou and A. L. Nevai, Asymptotic profiles of the steady states for an SIS epidemic reaction–diffusion model, Discrete Contin. Dyn. Syst. 21 (2008), 1–20. 10.3934/dcds.2008.21.1Suche in Google Scholar

[2] Z. Bai, R. Peng and X.-Q. Zhao, A reaction–diffusion malaria model with seasonality and incubation period, J. Math. Biol. 77 (2016), 201–228. 10.1007/s00285-017-1193-7Suche in Google Scholar PubMed

[3] L. S. Bastos, D. A. M. Villela, L. M. De Carvalho, O. G. Cruz, M. F. C. Gomes, B. Durovni, et al. Zika in Rio de Janeiro: Assessment of basic reproduction number and comparison with dengue outbreaks, Epid. Infec. 145 (2016), 1649–1657. 10.1017/S0950268817000358Suche in Google Scholar PubMed PubMed Central

[4] Y. Cai, Z. Ding, B. Yang, Z. Peng, and W. Wang, Transmission dynamics of Zika virus with spatial structure a case study in Rio De Janeiro, Brazil, Physica A. 514 (2019), 729–740. 10.1016/j.physa.2018.09.100Suche in Google Scholar

[5] R. S. Cantrell and C. Cosner, Spatial Ecology via Reaction-Diffusion Equation, Wiley, Chichester, 2003. 10.1002/0470871296Suche in Google Scholar

[6] R. Cui and Y. Lou, A spatial SIS model in advective heterogeneous environments, J. Differ. Equ. 261 (2016), 3305–3343. 10.1016/j.jde.2016.05.025Suche in Google Scholar

[7] R. Cui, K.-Y. Lam, and Y. Lou, Dynamics and asymptotic profiles of steady states of an epidemic model in advective environments, J. Differ. Equ. 263 (2017), 2343–2373. 10.1016/j.jde.2017.03.045Suche in Google Scholar

[8] R. Cui, H. Li, R. Peng, and M. Zhou, Concentration behavior of endemic equilibrium for a reaction–diffusion–advection SIS epidemic model with mass action infection mechanism, Cal. Var. Par. Diff. Equ. 60 (2021), 184. 10.1007/s00526-021-01992-wSuche in Google Scholar

[9] W. E. Fitzgibbon, M. Langlais, and J. J. Morgan, A reaction–diffusion system on noncoincident spatial domains modeling the circulation of a disease between two host populations, Differ. Int. Equ. 17 (2004), 781–802. 10.57262/die/1356060329Suche in Google Scholar

[10] W. E. Fitzgibbon, M. Langlais, F. Marpeau and J. J. Morgan, Modelling the circulation of a disease between two host populations on non-coincident spatial domains, Biol. Invasions. 7 (2005), 863–875. 10.1007/s10530-005-5210-1Suche in Google Scholar

[11] W. E. Fitzgibbon, J. J. Morgan and G. F. Webb, An outbreak vector-host epidemic model with spatial structure: the 2015-2016 Zika outbreak in Rio De Janeiro, Theor. Biol. Med. Modell 14 (2017), 7. 10.1186/s12976-017-0051-zSuche in Google Scholar PubMed PubMed Central

[12] H. I. Freedman and X.-Q. Zhao, Global asymptotics in some quasimonotone reaction–diffusion systems with delays, J. Differ. Equ. 137 (1997), 340–362. 10.1006/jdeq.1997.3264Suche in Google Scholar

[13] J. K. Hale, Asymptotic Behavior of Dissipative Systems, American Mathematical Society, Providence, 1988. Suche in Google Scholar

[14] P. Hess, Periodic-Parabolic Boundary Value Problems and Positivity, Longman Scientifie & Technical, Essex, 1991. Suche in Google Scholar

[15] K. Kuto, H. Matsuzawa and R. Peng, Concentration profile of endemic equilibrium of a reaction diffusion advection SIS epidemic model, Cal. Var. Par. Diff. Equ. 56 (2017), 56–112. 10.1007/s00526-017-1207-8Suche in Google Scholar

[16] X. Lai and X. Zou, Repulsion effect on superinfecting virions by infected cells, Bull. Math. Biol. 76 (2014), 2806–2833. 10.1007/s11538-014-0033-9Suche in Google Scholar PubMed

[17] K.-Y. Lam and Y. Lou, Asymptotic behavior of the principal eigenvalue for cooperative elliptic systems and applications, J. Differ. Equ. 28 (2016), 29–48. 10.1007/s10884-015-9504-4Suche in Google Scholar

[18] H. Li, R. Peng, and F.-B. Wang, Varying total population enhances disease persistence: Qualitative analysis on a diffusive epidemic model, J. Differ. Equ. 262 (2017), 885–913. 10.1016/j.jde.2016.09.044Suche in Google Scholar

[19] Y. Lou and X.-Q. Zhao, A reaction–diffusion malaria model with incubation period in the vector population, J. Math. Biol. 62 (2011), 543–568. 10.1007/s00285-010-0346-8Suche in Google Scholar PubMed

[20] P. Magal and X.-Q. Zhao, Global attractors and steady states for uniformly persistent dynamical systems, SIAM J. Math. Anal. 37 (2005), 251–275. 10.1137/S0036141003439173Suche in Google Scholar

[21] P. Magal, G. Webb, and Y. Wu, On a vector-host epidemic model with spatial structure, Nonlinearity 31 (2018), 5589–5614. 10.1088/1361-6544/aae1e0Suche in Google Scholar

[22] P. Magal, G. Webb and Y. Wu, On the basic reproduction number of reaction–diffusion epidemic models, SIAM J. Appl. Math. 79 (2019), no. 1, 284–304. 10.1137/18M1182243Suche in Google Scholar

[23] L. Pu, Z. Lin, and Y. Lou, A West Nile virus nonlocal model with free boundaries and seasonal succession, J. Math. Biol. 86 (2023), 25. 10.1007/s00285-022-01860-xSuche in Google Scholar PubMed

[24] P. Song, Y. Lou, and Y. Xiao, A spatial SEIRS reaction–diffusion model in heterogeneous environment, J. Differ. Equ. 267 (2019), 5084–5114. 10.1016/j.jde.2019.05.022Suche in Google Scholar

[25] W. Troy, Symmetry properties in systems of semilinear elliptic equations, J. Differ. Equ. 42 (1981), 400–413. 10.1016/0022-0396(81)90113-3Suche in Google Scholar

[26] J. Wang and H. Lu, Dynamics and profiles of a degenerated reaction–diffusion host-pathogen model with apparent and inapparent infection period, Commun. Nonlinear Sci. Numer. Simulat. 125 (2023), 107318. 10.1016/j.cnsns.2023.107318Suche in Google Scholar PubMed PubMed Central

[27] J. Wang and H. Lu, Analysis of a diffusive host-pathogen epidemic model with two-stage mechanism in a spatially heterogeneous environment, Math. Methods Appl. Sci. 46 (2023), 14657–14688. 10.1002/mma.9340Suche in Google Scholar

[28] W. Wang and X.-Q. Zhao, Basic reproduction numbers for reaction–diffusion epidemic models, SIAM J. Appl. Dyn. Syst. 11 (2012), no. 4, 1652–1673. 10.1137/120872942Suche in Google Scholar

[29] X. Wang and X.-Q. Zhao, A periodic vector-bias malaria model with incubation period, SIAM J. Appl. Math. 77 (2017), 181–201. 10.1137/15M1046277Suche in Google Scholar

[30] J. Wang and Y. Chen, Threshold dynamics of a vector-borne disease model with spatial structure and vector-bias, Appl. Math. Lett. 100 (2020), 106052. 10.1016/j.aml.2019.106052Suche in Google Scholar

[31] K. Wang, H. Wang, and H. Zhao, Aggregation and classification of spatial dynamics of vector-borne disease in advective heterogeneous environment, J. Differ. Equ. 343 (2023), 285–331. 10.1016/j.jde.2022.10.013Suche in Google Scholar

[32] K. Wang, H. Wang, and H. Zhao, On the role of advection in a spatial epidemic model with general boundary conditions, J. Differ. Equ. 386 (2024), 45–79. 10.1016/j.jde.2023.12.016Suche in Google Scholar

[33] Y. Wu and X. Zou, Asymptotic profiles of steady states for a diffusive SIS epidemic model with mass action infection mechanism, J. Differ. Equ. 261 (2016), 4424–4447. 10.1016/j.jde.2016.06.028Suche in Google Scholar

[34] Q. Ye, Z. Li, M. Wang, and Y. Wu, Introduction to Reaction-Diffusion Equations, Science Press, Beijing, 2011. Suche in Google Scholar

[35] L. Zhang, Z. Wang and X.-Q. Zhao, Threshold dynamics of a time periodic reaction–diffusion epidemic model with latent period, J. Differ. Equ. 258 (2015), 3011–3036. 10.1016/j.jde.2014.12.032Suche in Google Scholar

[36] M. Zhu, Z. Lin, and L. Zhang, The asymptotic profile of a dengue model on a growing domain driven by climate change, Appl. Math. Model. 83 (2020), 470–486. 10.1016/j.apm.2020.03.006Suche in Google Scholar

Received: 2024-02-02
Revised: 2024-05-17
Accepted: 2024-09-23
Published Online: 2024-10-15

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

  1. Regular Articles
  2. Existence of normalized peak solutions for a coupled nonlinear Schrödinger system
  3. Orbital stability of the trains of peaked solitary waves for the modified Camassa-Holm-Novikov equation
  4. Global boundedness in a two-dimensional chemotaxis system with nonlinear diffusion and singular sensitivity
  5. Existence and uniqueness of solution for a singular elliptic differential equation
  6. The bounded variation capacity and Sobolev-type inequalities on Dirichlet spaces
  7. Vanishing and blow-up solutions to a class of nonlinear complex differential equations near the singular point
  8. Existence, uniqueness, localization and minimization property of positive solutions for non-local problems involving discontinuous Kirchhoff functions
  9. Concentration phenomena for a fractional relativistic Schrödinger equation with critical growth
  10. Beyond the classical strong maximum principle: Sign-changing forcing term and flat solutions
  11. Monotonicity of solutions for parabolic equations involving nonlocal Monge-Ampère operator
  12. On a nonlinear Robin problem with an absorption term on the boundary and L1 data
  13. Multiple solutions for the quasilinear Choquard equation with Berestycki-Lions-type nonlinearities
  14. Gradient estimates for a class of higher-order elliptic equations of p-growth over a nonsmooth domain
  15. Global existence and decay estimates of the classical solution to the compressible Navier-Stokes-Smoluchowski equations in ℝ3
  16. Global existence and finite-time blowup for a mixed pseudo-parabolic r(x)-Laplacian equation
  17. Multiple positive solutions for a class of concave-convex Schrödinger-Poisson-Slater equations with critical exponent
  18. A minimization problem with free boundary for p-Laplacian weakly coupled system
  19. Multiplicity of semiclassical solutions for a class of nonlinear Hamiltonian elliptic system
  20. k-convex solutions for multiparameter Dirichlet systems with k-Hessian operator and Lane-Emden type nonlinearities
  21. Infinitely many solutions for Hamiltonian system with critical growth
  22. On optimal control in a nonlinear interface problem described by hemivariational inequalities
  23. Variational–hemivariational system for contaminant convection–reaction–diffusion model of recovered fracturing fluid
  24. Potential and monotone homeomorphisms in Banach spaces
  25. Critical fractional Schrödinger-Poisson systems with lower perturbations: the existence and concentration behavior of ground state solutions
  26. Supercritical Hénon-type equation with a forcing term
  27. Concentration of blow-up solutions for the Gross-Pitaveskii equation
  28. Mountain-pass-type solutions for Schrödinger equations in R2 with unbounded or vanishing potentials and critical exponential growth nonlinearities
  29. Regularity for critical fractional Choquard equation with singular potential and its applications
  30. Double phase anisotropic variational problems involving critical growth
  31. Normalized solutions of NLS equations with mixed nonlocal nonlinearities
  32. Nontrivial solutions for resonance quasilinear elliptic systems
  33. Standing waves for Choquard equation with noncritical rotation
  34. Low regularity conservation laws for Fokas-Lenells equation and Camassa-Holm equation
  35. Modified quasilinear equations with strongly singular and critical exponential nonlinearity
  36. Limit profiles and the existence of bound-states in exterior domains for fractional Choquard equations with critical exponent
  37. Nests of limit cycles in quadratic systems
  38. Regularity of minimizers for double phase functionals of borderline case with variable exponents
  39. Boundedness, existence and uniqueness results for coupled gradient dependent elliptic systems with nonlinear boundary condition
  40. Ground state solutions for magnetic Schrödinger equations with polynomial growth
  41. Nonoccurrence of Lavrentiev gap for a class of functionals with nonstandard growth
  42. Dynamics for wave equations connected in parallel with nonlinear localized damping
  43. Boussinesq's equation for water waves: Asymptotics in Sector I
  44. Optimal global second-order regularity and improved integrability for parabolic equations with variable growth
  45. Normalized solutions of Schrödinger equations involving Moser-Trudinger critical growth
  46. Normalized solutions for the double-phase problem with nonlocal reaction
  47. Normalized solutions for Sobolev critical fractional Schrödinger equation
  48. Well-posedness of Cauchy problem of fractional drift diffusion system in non-critical spaces with power-law nonlinearity
  49. Improved results on planar Klein-Gordon-Maxwell system with critical exponential growth
  50. Existence and multiplicity of solutions for a new p(x)-Kirchhoff equation
  51. Quasiconvex bulk and surface energies: C1,α regularity
  52. Time decay estimates of solutions to a two-phase flow model in the whole space
  53. Bounds for the sum of the first k-eigenvalues of Dirichlet problem with logarithmic order of Klein-Gordon operators
  54. The properties of a new fractional g-Laplacian Monge-Ampère operator and its applications
  55. A fractional profile decomposition and its application to Kirchhoff-type fractional problems with prescribed mass
  56. Cauchy problem for a non-Newtonian filtration equation with slowly decaying volumetric moisture content
  57. Multiplicity of normalized semi-classical states for a class of nonlinear Choquard equations
  58. The second Yamabe invariant with boundary
  59. Peaked solitary waves and shock waves of the Degasperis-Procesi-Kadomtsev-Petviashvili equation
  60. Normalized solutions for the Choquard equations with critical nonlinearities
  61. Boundedness and long-time behavior in a parabolic-elliptic system arising from biological transport networks
  62. Initial boundary value problem and exponential stability for the planar magnetohydrodynamics equations with temperature-dependent viscosity
  63. Nonexistence of mean curvature flow solitons with polynomial volume growth immersed in certain semi-Riemannian warped products
  64. Analysis of a vector-borne disease model with vector-bias mechanism in advective heterogeneous environment
  65. Normalized solutions for the Kirchhoff equation with combined nonlinearities in ℝ4
  66. Nonexistence of the compressible Euler equations with space-dependent damping in high dimensions
  67. Multiplicity of solutions for a nonhomogeneous quasilinear elliptic equation with concave-convex nonlinearities
  68. On semilinear inequalities involving the Dunkl Laplacian and an inverse-square potential outside a ball
  69. Besov regularity for the elliptic p-harmonic equations in the non-quadratic case
  70. Uniqueness and nondegeneracy of ground states for Δ u + u = ( I α u 2 ) u in R 3 when α is close to 2
  71. Existence of solutions for a class of quasilinear Schrödinger equations with Choquard-type nonlinearity
  72. Weighted Hardy-Adams inequality on unit ball of any even dimension
  73. Existence and regularity for a p-Laplacian problem in ℝN with singular, convective, and critical reaction
  74. Temporal periodic solutions of non-isentropic compressible Euler equations with geometric effects
  75. Nodal solutions for a zero-mass Chern-Simons-Schrödinger equation
  76. The modified quasi-boundary-value method for an ill-posed generalized elliptic problem
  77. Nonlocal heat equations with generalized fractional Laplacian
  78. Choquard equations with recurrent potentials
  79. Local and global well-posedness of the Maxwell-Bloch system of equations with inhomogeneous broadening
  80. The Riemann problem for two-layer shallow water equations with bottom topography
  81. Global stability and asymptotic profiles of a partially degenerate reaction diffusion Cholera model with asymptomatic individuals
  82. On Kirchhoff-Schrödinger-Poisson-type systems with singular and critical nonlinearity
  83. Energy-variational solutions for viscoelastic fluid models
  84. Stability on 3D Boussinesq system with mixed partial dissipation
  85. Existence and multiplicity results for non-autonomous second-order Hamiltonian systems
  86. Erratum
  87. Erratum to “Normalized solutions for the Kirchhoff equation with combined nonlinearities in ℝ4
Heruntergeladen am 19.9.2025 von https://www.degruyterbrill.com/document/doi/10.1515/anona-2024-0045/html
Button zum nach oben scrollen