一类带有疫苗接种传染病模型的全局稳定性和分岔分析

分析了一类带有疫苗接种的SEIR新型冠状病毒感染模型,讨论系统的边界平衡点和内部平衡点存在的参数条件,通过再生矩阵的方法计算基本再生数,给出了平衡点的局部稳定性,并进一步构造Lyapunov函数和变分矩阵的方法分析系统平衡点的全局渐近稳定性,得到当基本再生数R₀<1时,系统存在一个全局渐近稳定的边界平衡点;当基本再生数R₀>1时,系统的边界平衡点是不稳定的,同时还存在一个全局渐近稳定的内部平衡点.利用分岔理论中的Sotomayor定理证明了在R₀=1处,系统在边界平衡点P₀附近将会发生跨临界分岔.最后通过数值模拟展示系统稳定性的情况.     

一类具有时滞和Michaelis-Menten型收获的捕食系统的稳定性与Hopf分支分析

探讨了一类具有时滞和非线性Michaelis-Menten型收获的捕食系统.利用微分方程的稳定性理论和Hopf分支理论,研究模型的动力学行为.分析了系统存在唯一正平衡点的条件,系统正平衡点渐近稳定的条件,并且给出了滞量作为参数时存在临界值使系统在一定范围内正平衡点仍保持稳定,而在其等于临界滞量时系统在正平衡点处出现Hopf分支的结论.     

一类松籽、松鼠、幼苗的征税模型分析

运用微分方程理论,研究了一类非线性的红松种群征税模型,得到了该系统的平衡点,证明了该系统正平衡点的局部渐进稳定性和正平衡点的全局吸引域,利用Pontryagin 最大值原理给出了最优征税策略.     

仅含两个稳定平衡点的4D分数阶系统的动力学与同步

本文构造了一个新的四维分数阶混沌系统,与至少含有一个不稳定平衡点的一般分数阶混沌系统不同的是,该系统仅有两个稳定平衡点.首先给出了两个平衡点局部渐近稳定的充分条件,通过数值模拟验证了该系统的混沌吸引子与两个稳定平衡点共存.然后,基于分数阶Lyapunov稳定性理论,在误差系统保留非线性项的情况下,利用反馈控制实现了此系统的同步,数值模拟进一步证实了结论的正确性.     

两种群共生关系的模型分析

建立了两种群在偏利和偏害共生作用下的数学模型,分析了两种系统的各平衡点的稳定性,得出了两系统各存在唯一的稳定平衡点的结论,并对模型及其平衡点的生物学意义做了讨论.     

具HollingⅡ类功能反应函数的食饵-捕食系统的定性分析

研究具有非线性密度制约的HollingⅡ型功能反应的食饵一捕食两种群模型,讨论了该系统的非负平衡点性态和其对应的反映扩散系统正平衡点的稳定性,最后证明了系统在平衡点外围至少存在一个稳定极限环．     

一类食饵具有传染病的捕食-被捕食模型的分析

建立并分析了食饵具有传染病的生态-流行病模型,讨论了系统平衡点的存在性,利用特征根法对系统的边界平衡点进行局部渐近稳定性分析,并通过构造合适的Liapunov函数得到了该系统的两个边界平衡点的全局渐近稳定性的充分条件。     

时滞类Lorenz系统的Hopf分支

对类Lorenz系统的状态变量加上时滞得到一个泛函微分动力系统--时滞类Lorenz系统。首先给出了该系统仅存在零平衡点的条件,然后根据系统在零平衡点处的线性化系统对应的特征方程根的分布情况,给出了系统在零平衡点处稳定性和发生Hopf分支的条件,最后通过一些数值模拟验证了所得结论的正确性。     

具有非线性传染率的时滞SIQR模型的稳定性分析

建立了具有时滞及非线性发生率的SIQR传染病模型,通过对无病平衡点和正平衡点处的特征方程的讨论,可得到在这两个平衡点处的局部渐近稳定性,进而得到了系统在两个平衡点处的全局渐近稳定性.     

一类高阶差分方程系统的稳定性

研究了一类具有初值的高阶差分方程系统平衡点的稳定性问题,得到了平衡点处稳定、局部渐近稳定性、全局渐近稳定性的充分条件,讨论了正平衡点处解的振动性问题.     

卡思卡特城堡

It is worthy of noting that, whilst Crookston Castle witnessed the earlier and happier portion of Mary's variegated life,     

不同的吃喝玩乐

一、吃和喝吃苹果 eat an apple, 吃药 take medicine,吃糖 have some sweets,吃饭 have one's meals,吃馆子 dine out,吃惊 be surprised/     

漏洞百出的教育

Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help?     

Western and Eastern culture differences in commercial field

The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity.     

只要努力,不要后悔

There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love.     

浅谈移民问题

Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject.     

Sister Carrie, an Adherent of Desires

Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities.     

Improvement of one-cycle controller by use of proportional integral differential controller

1.IntroductionOne-cyclecontrolmethod,whichwasproposedaboutonedecadeago[1],hasbecomeanattractivemethodinspecialfieldssuchaspowerfactorcorrection[2-6],switchingamplifiers[7,8],etc.Themainideaofthiscontrollerisbasedonintegrationofdiodevoltageinone-cycleandforcesittobeexactlyequaltothereferencevalue.Themainadvantageofthiscontrollerisitsrealtimeabilitytorejectthevariationofinputvoltage[1].Despitethisgreatability,ithasnogoodperformancesinrejectingofloaddisturbanceandfollowingreferencecommands.Espec…     

风的曲线

Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose.