Analysis of Geometric Invariants for Three Types of Bifurcations in 2D Differential Systems

Little is known about bifurcations in two-dimensional (2D) differential systems from the viewpoint of Kosambi–Cartan–Chern (KCC) theory. Based on the KCC geometric invariants, three types of static bifurcations in 2D differential systems, i.e. saddle-node bifurcation, transcritical bifurcation, and pitchfork bifurcation, are discussed in this paper. The dynamics far from fixed points of the systems generating bifurcations are characterized by the deviation curvature and nonlinear connection. In the nonequilibrium region, the nonlinear stability of systems is not simple but involves alternation between stability and instability, even though systems are invariably Jacobi-unstable. The results also indicate that the dynamics in the nonequilibrium region are node-like for three typical static bifurcations.

Neimark-Sacker, flip and transcritical bifurcation in a symmetric system of difference equations with exponential terms

In this paper, we study the conditions under which the following symmetric system of difference equations with exponential terms: \[ x_{n+1} =a_1\frac{y_n}{b_1+y_n} +c_1\frac{x_ne^{k_1-d_1x_n}}{1+e^{k_1-d_1x_n}},\] \[ y_{n+1} =a_2\frac{x_n}{b_2+x_n} +c_2\frac{y_ne^{k_2-d_2y_n}}{1+e^{k_2-d_2y_n}}\] where $a_i$, $b_i$, $c_i$, $d_i$, $k_i$, for $i=1,2$, are real constants and the initial values $x_0$, $y_0$ are real numbers, undergoes Neimark-Sacker, flip and transcritical bifurcation. The analysis is conducted applying center manifold theory and the normal form bifurcation analysis.

Dynamical analysis of an aquatic amensalism model with non-selective harvesting and Allee effect

<abstract><p>In this paper, in order to explore the inhibition mechanism of algicidal bacteria on algae, we constructed an aquatic amensalism model with non-selective harvesting and Allee effect. Mathematical works mainly gave some critical conditions to guarantee the existence and stability of equilibrium points, and derived some threshold conditions for saddle-node bifurcation and transcritical bifurcation. Numerical simulation works mainly revealed that non-selective harvesting played an important role in amensalism dynamic relationship. Meanwhile, we proposed some biological explanations for transcritical bifurcation and saddle-node bifurcation from the aspect of algicidal bacteria controlling algae. Finally, all these results were expected to be useful in studying dynamical behaviors of aquatic amensalism ecosystems and biological algae controlling technology.</p></abstract>

Applying the quasi-steady-state approximation to the autocatalytic zymogen activation: A novel general methodology for scaling analysis

<p><br></p><table><tr><td>A zymogen is an inactive precursor of an enzyme that needs to go through a chemical change to become an active enzyme. The general intermolecular mechanism for the autocatalytic activation of zymogens is governed by the single-enzyme, single-substrate catalyzed reaction following the Michaelis-Menten mechanism of enzyme action, where the substrate is the zymogen and the product is the same enzyme that is catalyzing the reaction. In this article we investigate the nonlinear chemical dynamics of the intermolecular autocatalytic zymogen activation reaction mechanism. In so doing, we develop a general strategy for obtaining dimensionless parameters that, when sufficiently small, legitimize the application of the quasi-steady-state approximation. Our methodology combines energy methods and exploits the phase-plane geometry of the mathematical model, and we obtain sufficient conditions that support the validity of the standard, reverse and total quasi-steady-state approximations for the intermolecular autocatalytic zymogen activation reaction mechanism. The utility of the procedure we develop is that it circumnavigates the direct need for a priori timescale estimation, scaling, and non-dimensionalization. At the same time, a novel result emerges from our analysis: the discovery of a dynamic transcritical bifurcation that exists in the singular limit of the model equations. Moreover, associated with the dynamic transcritical bifurcation is an imperfect term. We prove that when the imperfect term vanishes and the singular vector field is perturbed, there exists a canard that follows a repulsive slow invariant manifold over timescales of <i>O</i>(1). This is the first report of such a solution for the intermolecular and autocatalytic zymogen activation reaction. By extension, our results illustrate that canards also exist in the classic single enzyme, single-substrate reversible Michaelis-Menten reaction mechanism.</td></tr></table>

Applying the quasi-steady-state approximation to the autocatalytic zymogen activation: A novel general methodology for scaling analysis

<p><br></p><table><tr><td>A zymogen is an inactive precursor of an enzyme that needs to go through a chemical change to become an active enzyme. The general intermolecular mechanism for the autocatalytic activation of zymogens is governed by the single-enzyme, single-substrate catalyzed reaction following the Michaelis-Menten mechanism of enzyme action, where the substrate is the zymogen and the product is the same enzyme that is catalyzing the reaction. In this article we investigate the nonlinear chemical dynamics of the intermolecular autocatalytic zymogen activation reaction mechanism. In so doing, we develop a general strategy for obtaining dimensionless parameters that, when sufficiently small, legitimize the application of the quasi-steady-state approximation. Our methodology combines energy methods and exploits the phase-plane geometry of the mathematical model, and we obtain sufficient conditions that support the validity of the standard, reverse and total quasi-steady-state approximations for the intermolecular autocatalytic zymogen activation reaction mechanism. The utility of the procedure we develop is that it circumnavigates the direct need for a priori timescale estimation, scaling, and non-dimensionalization. At the same time, a novel result emerges from our analysis: the discovery of a dynamic transcritical bifurcation that exists in the singular limit of the model equations. Moreover, associated with the dynamic transcritical bifurcation is an imperfect term. We prove that when the imperfect term vanishes and the singular vector field is perturbed, there exists a canard that follows a repulsive slow invariant manifold over timescales of <i>O</i>(1). This is the first report of such a solution for the intermolecular and autocatalytic zymogen activation reaction. By extension, our results illustrate that canards also exist in the classic single enzyme, single-substrate reversible Michaelis-Menten reaction mechanism.</td></tr></table>

Efficacy of Isolation as a Control Strategy for Ebola Outbreaks in Combination with Vaccination

In this research work, we have developed and analyzed a deterministic epidemiological model with a system of nonlinear differential equations for controlling the spread of Ebola virus disease (EVD) in a population with vital dynamics (where birth and death rates are not equal). The model examines the disease transmission dynamics with isolation from exposed and infected human class and effect of vaccination in susceptible human population through stability analysis and bifurcation analysis. The model exhibits two steady state equilibria, namely, disease-free and endemic equilibrium. Next generation matrix method is used to find the expression for [Formula: see text] (the basic reproduction number). Local and global stability of diseases-free equilibrium are shown using nonsingular M-matrix technique and Lyapunov’s theorem, respectively. The existence and local stability of endemic equilibrium are explored under certain conditions. All numerical data entries are supported by various authentic sources. The simulation study is done using MATLAB code 45 which uses Runge–Kutta method of fourth order and we plot the time series and bifurcation diagrams which support our analytical findings. Stability analysis of the model shows that the disease-free equilibrium is locally as well as globally asymptotically stable if [Formula: see text] and endemic equilibrium is locally asymptotically stable in absence of vaccination if [Formula: see text]. Using central manifold theorem, the presence of transcritical bifurcation for a threshold value of the transmission rate parameter [Formula: see text] when [Formula: see text] passes through unity and backward bifurcation (i.e. transcritical bifurcation in opposite direction) for some higher value of [Formula: see text] are established. Our simulation study shows that isolation of exposed and infected individuals can be used as a more effective tool to control the spreading of EVD than only vaccination.