膨润土负载型固体酸的制备、表征及催化乙酰水杨酸合成反应

膨润土;制备;负载型固体酸;乙酰水杨酸;催化     

Bifurcation analysis of a delayed epidemic model

In this paper, Hopf bifurcation for a delayed SIS epidemic model with stage structure and nonlinear incidence rate is investigated. Through theoretical analysis, we show the positive equilibrium stability and the conditions that Hopf bifurcation occurs. Applying the normal form theory and the center manifold argument, we derive the explicit formulas determining the properties of the bifurcating periodic solutions. In addition, we also study the effect of the inhibition effect on the properties of the bifurcating periodic solutions. To illustrate our theoretical analysis, some numerical simulations are also included.     

Emergence of Strange Spatial Pattern in a Spatial Epidemic Model

Pattern formation of a spatial epidemic model with nonlinear incidence rate hI^2 S/（1 ＋ αI^2） is investigated. Our results show that strange spatial dynamics, i.e., filament-like pattern, can be obtained by both mathematical analysis and numerical simulation, which are different from the previous results in the spatial epidemic model such as stripe-like or spotted or coexistence of both pattern and so on. The obtained results well extend the finding of pattern formation in the epidemic model and may well explain the distribution of the infected of some epidemic.     

吡啶-3-甲醛缩氨基硫脲合镍(Ⅱ)、锌(Ⅱ)配合物的合成、晶体结构及生物活性

本文合成并表征了吡啶-3-甲醛缩氨基硫脲(HL)合镍(Ⅱ)、锌(Ⅱ)配合物。在配合物[NiL₂] (1)中,镍(Ⅱ)离子与来自2个脱氢配体的2个氮原子和2个硫原子配位,形成四配位的平面正方形构型。在配合物[Zn(HL)₂(C₂H₅OH)₂(H₂O)₂](NO₃)₂ (2)中,锌(Ⅱ)     

Motion of spiral tip driven by local forcing in excitable media

We study the motion of a spiral wave controlled by a local periodic forcing imposed on a region around the spiral tip in an excitable medium. Three types of trajectories of spiral tip are observed： the epicycloid-like meandering, the resonant drift, and the hypocycloid-like meandering. The frequency of the spiral is sensitive to the local periodic forcing. The dependency of spiral frequency on the amplitude and size of local periodic forcing are presented. In addition, we show how the drift speed and direction are adjusted by the amplitude and phase of local periodic forcing, which is consistent with a theoretical analysis based on the weak deformation approximation.     

Transmission dynamics of COVID-19 in Wuhan,China: effects of lockdown and medical resources

Nonlinear Dynamics - Due to the strong infectivity of COVID-19, it spread all over the world in about three months and thus has been studied from different aspects including its source of...     

Pattern formation induced by cross-diffusion in a predator--prey system

This paper considers the Holling-Tanner model for predator-prey with self and cross-diffusion. From the Turing theory, it is believed that there is no Turing pattern formation for the equal self-diffusion coefficients. However, combined with cross-diffusion, it shows that the system will exhibit spotted pattern by both mathematical analysis and numerical simulations. Furthermore, asynchrony of the predator and the prey in the space. The obtained results show that cross-diffusion plays an important role on the pattern formation of the predator-prey system.     

Impact of media coverage on epidemic spreading in complex networks

An SIS network model incorporating the influence of media coverage on transmission rate is formulated and analyzed. We calculate the basic reproduction number _R0$R_0$ by utilizing the local stability of the disease-free equilibrium. Our results show that the disease-free equilibrium is globally asymptotically stable and that the disease dies out if _R0$R_0$ is below 1; otherwise, the disease will persist and converge to a unique positive stationary state. This result may suggest effective control strategies to prevent disease through media coverage and education activities in finite-size scale-free networks. Numerical simulations are also performed to illustrate our results and to give more insights into the dynamical process.     

Self-organized wave pattern in a predator-prey model

In this paper, pattern formation of a predator-prey model with spatial effect is investigated. We obtain the conditions for Hopf bifurcation and Turing bifurcation by mathematical analysis. When the values of the parameters can ensure a stable limit cycle of the no-spatial model, our study shows that the spatially extended models have spiral waves dynamics. Moreover, the stability of the spiral wave is given by the theory of essential spectrum. Furthermore, although the environment is heterogeneous, the system still exhibit spiral waves. The obtained results confirm that diffusion can form the population in the stable motion, which well enrich the finding of spatiotemporal dynamics in the predator-prey interactions and may well explain the field observed in some areas.