不难证明,模型(2)在边界条件(3)和初始条件(4)下有唯一的非负解。
1 基本再生率与稳态解
显然,模型(2)总存在一个未感染稳态解E0(x0,0,0),其中x0=s/d。
使用文献[14]中介绍的下一代矩阵方法,通过计算可以得到病毒的基本再生率的表达式为
如果模型(2)存在病毒感染稳态解E*(x*,y*(a),v*),则它必满足下列方程组:
(6)
从式(6)的第2和第4个方程解得:
y*(a)=x*f(v*)e-∫a0δ(ε)dε,
(7)
将式(7)代入式(6)的第3个方程可得:
(8)
因此,若模型(2)存在病毒感染稳态解,则以下方程组有正根。
(9)
定理1当R0>1时,模型(2)存在唯一的病毒感染稳态解E*。
证明考虑方程组(9)正根的存在性问题。若x*为正,方程组(9)等价于
(10)
令
计算可得:
由拉格朗日中值定理可知,在(0,v)上至少存在1点ξ,使得:
2 局部稳定性
定理2当R0<1时,模型(2)的未感染稳态解E0是局部渐近稳定的。
证明将模型(2)在E0处线性化并引入扰动变量:
得到:
(11)
求式(11)满足下列形式:
(12)
的非平凡解。
将式(12)代入式(11)可得:
(13)
从式(13)的第2和第4个方程解得:
(14)
将式(14)代入式(13)的第3个方程,整理可得模型(2)在E0处的特征方程:
(15)
下面用反正法证明,当R0<1时,方程(15)的根都具有负实部。
假设方程(15)存在一个根λ1,满足Re(λ1)≥0。则:
显然,这与R0<1矛盾。因此,当R0<1时,方程(15)的根都具有负实部,E0是局部渐近稳定的。
定理3当R0>1时,模型(2)的病毒感染稳态解E*是局部渐近稳定的。
证明将模型(2)在E*处线性化并引入扰动变量:
x2(t)=x(t)-x*,y2(a,t)=y(a,t)-y*(a),v2(t)=v(t)-v*,
得到:
(16)
求式(16)满足下列形式:
(17)
的非平凡解。
将式(17)代入式(16)可得:
(18)
从式(18)的第2和第4个方程解得:
(19)
从式(18)的第1个方程可以得到:
(λ+d+f(v*))c3=-f′(v*)x*c4,
(20)
将式(19)和式(20)代入式(18)的第3个方程,得到模型(2)在E*处的特征方程:
(21)
当R0>1时,由拉格朗日中值定理和条件(5)可得:
下面用反证法证明,当R0>1时,方程(21)的根都具有负实部。
假设方程(21)存在1个根λ1,满足Re(λ1)≥0,则:
显然,这是矛盾的。因此,当R0>1时,方程(21)的根都具有负实部,E*是局部渐近稳定的。
3 全局稳定性
笔者通过构造适当的Lyapunov泛函并应用LaSalle不变集原理来研究模型(2)的可行稳态解的全局稳定性。
定理4当R0<1时,模型(2)的未感染稳态解E0是全局渐近稳定的。
证明记
(22)
显然,在条件H2)和条件H3)下p(a)是有界的。p(a)的导数为
p′(a)=δ(a)p(a)-k(a),
(23)
构造Lyapunov泛函:
显然,V1(t)是非负的,且在E0处取得最小值0。沿着模型(2)的解对V1(t)求全导数可得:
(24)
使用分部积分法可以得到:
(25)
将式(25)代入式(24)可得:
(26)
当v(t)=0时,
当v(t)>0时,
由拉格朗日中值定理和条件(5)可知,存在ξ∈(0,v(t)),使得:
定理5当R0>1时,模型(2)的病毒感染稳态解E*是全局渐近稳定的。
证明构造Lyapunov泛函:
其中p(a)如式(22)中所定义。
显然,V1(t)是非负的,且在E*处取得最小值0。沿着模型(2)的解对V2(t)求全导数可得:
(27)
由
和
可得:
使用分部积分法得到:
(28)
在式(28)中:
(29)
由式(28)和式(29)推出:
(30)
将式(30)代入式(27),整理可得:
/
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Stability analysis of a viral infection dynamics model with infection age of cells and general saturated infection rate
LI Liangchen, XU Rui
(Basic Courses Department, Ordnance Engineering College, Shijiazhuang,Hebei 050003, China)
In order to understand the viral dynamics processes inclucding infection, duplicate, eliminate, etc. in human body, a viral infection model with infection age of cells and general saturated infection rate is investigated. It is proved that the model has a unique infected steady state when the basic reproduction ratio is greater than one unity. By analyzing the characteristic of relevant equations, the local stability of effective steady state is dislussed. By using suitable Lyapunov functional and LaSalle’s invariance principle, it is proved that when the basic reproduction ratio is less than one unity, the infection-free steady state is globally asymptotically stable; and when the basic reproduction ratio is greater than one unity, the infected steady state is globally asymptotically stable.
stability theory; infection age of cells; saturation infection rate; Lyapunov functional; LaSalle’s invariance principle
1008-1542(2016)04-0349-08
10.7535/hbkd.2016yx04006
2015-12-09;
2016-04-19;责任编辑:张军
国家自然科学基金(11371368)
李梁晨(1990—),男,河北唐山人,硕士研究生,主要从事微分方程与动力系统方面的研究。
E-mail:llc610@126.com
O175MSC(2010)主题分类:34N05
A
李梁晨,徐瑞.一类具有细胞感染年龄和一般饱和感染率的病毒感染动力学模型的稳定性分析[J].河北科技大学学报,2016,37(4):349-356.
LI Liangchen, XU Rui.Stability analysis of a viral infection dynamics model with infection age of cells and general saturated infection rate[J].Journal of Hebei University of Science and Technology,2016,37(4):349-356.