In this paper, we establish an infectious disease model of Tropidothorax elegans to study the impact of them on plants. Our model involves the time delay for Tropidothorax elegans to hatch eggs, which is influenced by temperature. Second, we theoretically analyze the existence and the stability of the equilibrium and the normal form near the Hopf bifurcating critical point. Next, we choose three groups of parameters for numerical simulations to verify theoretical analysis of our model. Then, based on numerical simulations, we give bioanalysis which are consistent with the patterns of Tropidothorax elegans pests, such as dying off in large numbers of adults during the winter and one or two generations a year.

This paper introduces diffusion into an immunosuppressive infection model with virus stimulation delay and Beddington-DeAngelis functional response. First, we study the stability of positive constant steady state solution and show that the Hopf bifurcation will exist under certain conditions. Second, we derive the normal form of the Hopf bifurcation for the model reduced on the center manifold by using the multiple time scales (MTS) method. Moreover, the direction and stability of the bifurcating periodic solution are investigated. Finally, we present numerical simulations to verify the results of theoretical analysis and provide corresponding biological explanations.

In this paper, a reaction-diffusion dual carbon model associated with Dirichlet boundary condition is proposed under the influence of economic development in China. First, we enumerate and analyse some influencing factors of carbon emission and carbon absorption, and select economic development as the influence factor of carbon emission. Second, we establish a model associated with dual carbon and analyse the existence and stability of equilibrium and the existence of bifurcations. Finally, we analyse and predict for the value of parameters. Numerical simulations are presented to support our theory results. Combined with theoretical analysis and numerical simulations, we obtain that China can achieve carbon peak before 2030. If we want to achieve carbon neutral before 2060, it requires efforts from all of parts of society. Therefore, we put forward some practical suggestions to achieve carbon neutrality and carbon peak on schedule in China for the next few decades.

The excessive emission of greenhouse gases leads to abnormal climate change. Under this background, China puts forward the dual carbon target. In this paper, we use the analytic hierarchy process to determine the important influencing factor of carbon emissions. Next, we establish a delayed differential equation model of carbon emission-absorption under the influence of China's urbanization. We analyze the existence and stability of the positive equilibrium. Finally, we determine the ranges of parameters and study the impact of urbanization on China's dual carbon target through numerical simulations. The numerical simulation also shows that the system may have globally asymptotically stable equilibrium. Through the simulation results, we conclude whether the dual carbon target of China can be achieved by the scheduled time and give some suggestions that could be taken to achieve this target. The projected results provide some guidance for policy adjustments and also have practical significance in protecting the ecological environment.

As the COVID-19 continues threatening public health worldwide, when to vaccinate the booster shots becomes the hot topic. In this paper, based on the characteristics of COVID-19 and its vaccine, an $SAIR$ model associated with temporary immunity is proposed to study the effect on epidemic situation. Second, we theoretically analyze the existence and stability of equilibrium and the system undergoes Hopf bifurcation when delay passes through some critical values. Third, we study the dynamic properties of Hopf bifurcation and derive the normal form of Hopf bifurcation to determine the stability and direction of bifurcating periodic solutions. After that, numerical simulations are carried out to demonstrate the application of the theoretical results. Particularly, in order to ensure the validity, statistical analysis of data is conducted to determine the values for model parameters. Next, we study the impact of the infection rates on booster vaccination time to simulate the mutants, and the results are consistent with the facts. Finally, we predict the mean time of completing a round of vaccination worldwide with the help fitting and put forward some suggestions by comparing with the critical time of booster vaccination.