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Jana Kopfová

Publications and source records attributed to Jana Kopfová.

11 recordsLinked to original sources
arXiv2025

Global stability of Wright-type equations with negative Schwarzian

Simplicity of the $37/24$-global stability criterion announced by E.M. Wright in 1955 and rigorously proved by B. Bánhelyi et al in 2014 for the delayed logistic equation raised the question of its possible extension for other population models. In our study, we answer this question by extending the $37/24$-stability condition for the Wright-type equations with decreasing smooth nonlinearity $f$ which has a negative Schwarzian and satisfies the standard negative feedback and boundedness assumptions. The proof contains the construction and careful analysis of qualitative properties of certain bounding relations. To validate our conclusions, these relations are evaluated at finite sets of points; for this purpose, we systematically use interval analysis.

math.AP↗
arXiv2023

Bistable wavefronts in the delayed Belousov-Zhabotinsky reaction

We study the Murray adaptation of the Noyes-Field five-step model of the Belousov-Zhabotinsky (BZ) reaction in the case when a tuning parameter $r$, which determines the level of the bromide ion far ahead of the propagating wave, is bigger than 1 and when the delay in generation of the bromous acid is taken into account. The existence of wavefronts in the delayed BZ system was previously established only in the monostable situation with $r \in (0,1]$, the physically relevant bistable situation where $r >1$ (in real experiments $r$ varies between 5 and 50) was left open. We complete the study by showing that the BZ system with $r >1$ admits monotone traveling fronts. Note that one of the stable equilibria of the BZ model is not isolated. This circumstance does not allow the direct application of the topological or analytical methods previously elaborated for the analysis of the existence of bistable waves.

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arXiv2022

Two reasons for the appearance of pushed wavefronts in the Belousov-Zhabotinsky system with spatiotemporal interaction

We prove the existence of the minimal speed of propagation $c_*(r,b,K) \in [2\sqrt{1-r},2]$ for wavefronts in the Belousov-Zhabotinsky system with a spatiotemporal interaction defined by the convolution with (possibly, "fat-tailed") kernel $K$. The model is assumed to be monostable non-degenerate, i.e. $r\in (0,1)$. The slowest wavefront is termed pushed or non-linearly determined if its velocity $c_*(r,b,K) > 2\sqrt{1-r}$. We show that $c_*(r,b,K)$ is close to 2 if i) positive system's parameter $b$ is sufficiently large or ii) if $K$ is spatially asymmetric to one side (e.g. to the left: in such a case, the influence of the right side concentration of the bromide ion on the dynamics is more significant than the influence of the left side). Consequently, this reveals two reasons for the appearance of pushed wavefronts in the Belousov-Zhabotinsky reaction.

math.AP↗
arXiv2022

Global stability of SIR model with heterogeneous transmission rate modeled by the Preisach operator

In recent years, classical epidemic models, which assume stationary behavior of individuals, have been extended to include an adaptive heterogeneous response of the population to the current state of the epidemic. However, it is widely accepted that human behavior can exhibit history-dependence as a consequence of learned experiences. This history-dependence is similar to hysteresis effects that have been well-studied in control theory. To illustrate the importance of history-dependence for epidemic theory, we study dynamics of a variant of the SIRS model where individuals exhibit lazy-switch responses to prevalence dynamics. The resulting model, which includes the Preisach hysteresis operator, possesses a continuum of endemic equilibrium states characterized by different proportions of susceptible, infected and recovered populations. We discuss stability properties of the endemic equilibrium set and relate them to the degree of heterogeneity of the adaptive response. Our results support the argument that public health responses during the emergence of a new disease can have long-term consequences for subsequent management efforts. The main mathematical contribution of this work is a method of global stability analysis, which uses a family of Lyapunov functions corresponding to different branches of the hysteresis operator.

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arXiv2020

Effect of diagnostic testing on the isolation rate in a compartmental model with asymptomatic groups

We present two epidemiological models, which extend the classical SEIR model by accounting for the effect of indiscriminate quarantining, isolation of infected individuals based on testing and the presence of asymptomatic individuals. Given a constraint that limits the maximal number of simultaneous active cases, we demonstrate that the isolation rate, which enforces this constraint, decreases with the increasing testing rate. The models predict that massive testing allows to control the infection spread using a much lower isolation rate than in the case of indiscriminate quarantining. We also show that dynamics of infection are more sensitive to the parameters of the asymptomatic groups than the corresponding parameters of the symptomatic groups.

math.DS↗
arXiv2020

On pushed wavefronts of monostable equation with unimodal delayed reaction

We study the Mackey-Glass type monostable delayed reaction-diffusion equation with a unimodal birth function $g(u)$. This model, designed to describe evolution of single species populations, is considered here in the presence of the weak Allee effect ($g(u_0)>g'(0)u_0$ for some $u_0>0$). We focus our attention on the existence of slow monotonic traveling fronts to the equation: under given assumptions, this problem seems to be rather difficult since the usual positivity and monotonicity arguments are not effective. First, we solve the front existence problem for small delays, $h \in [0,h_p]$, where $h_p$ (given by an explicit formula) is optimal in a certain sense. Then we take a representative piece-wise linear unimodal birth function making possible explicit computation of traveling fronts. In this case, we find out that a) increase of delay can destroy asymptotically stable pushed fronts; b) the set of all admissible wavefront speeds has usual structure of a semi-infinite interval $[c_*, +\infty)$; c) for each $h\geq 0$, the pushed wavefront is unique (if it exists); d) pushed wave can oscillate slowly around the positive equilibrium for sufficiently large delays.

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arXiv2020

Dynamics of SIR model with vaccination and heterogeneous behavioral response of individuals modeled by the Preisach operator

We study global dynamics of an SIR model with vaccination, where we assume that individuals respond differently to dynamics of the epidemic. Their heterogeneous response is modeled by the Preisach hysteresis operator. We present a condition for the global stability of the infection-free equilibrium state. If this condition does not hold true, the model has a connected set of endemic equilibrium states characterized by different proportion of infected and immune individuals. In this case, we show that every trajectory converges either to an endemic equilibrium or to a periodic orbit. Under additional natural assumptions, the periodic attractor is excluded, and we guarantee the convergence of each trajectory to an endemic equilibrium state. The global stability analysis uses a family of Lyapunov functions corresponding to the family of branches of the hysteresis operator.

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arXiv2019

Nonlinearly determined wavefronts of the Nicholson's diffusive equation: when small delays are not harmless

By proving the existence of non-monotone and non-oscillating wavefronts for the Nicholson's blowflies diffusive equation (the NDE), we answer an open question raised in [16]. Surprisingly, these wavefronts can be observed only for sufficiently small delays. Similarly to the pushed fronts, obtained waves are not linearly determined. In contrast, a broader family of eventually monotone wavefronts for the NDE is indeed determined by properties of the spectra of the linearized equations. Our proofs use essentially several specific characteristics of the blowflies birth function (its unimodal form and the negativity of its Schwarz derivative, among others). One of the key auxiliary results of the paper shows that the Mallet-Paret--Cao--Arino theory of super-exponential solutions for scalar equations can be extended for some classes of second order delay differential equations. For the new type of non-monotone waves to the NDE, our numerical simulations also confirm their stability properties established by Mei et al.

math.CA↗
arXiv2019

On the geometric diversity of wavefronts for the scalar Kolmogorov ecological equation

In this work, we answer three fundamental questions concerning monostable travelling fronts for the scalar Kolmogorov ecological equation with diffusion and spatiotemporal interaction: these are the questions about their existence, uniqueness and geometric shape. In the particular case of the food-limited model, we give a rigorous proof of the existence of a peculiar, yet substantive non-linearly determined class of non-monotone and non-oscillating wavefronts. As regards to the scalar models coming from applications, this kind of wave solutions is analyzed here for the first time.

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arXiv2015

Traveling waves in the nonlocal KPP-Fisher equation: different roles of the right and the left interactions

We consider the nonlocal KPP-Fisher equation $u_t(t,x) = u_{xx}(t,x) + u(t,x)(1-(K *u)(t,x))$ which describes the evolution of population density $u(t,x)$ with respect to time $t$ and location $x$. The non-locality is expressed in terms of the convolution of $u(t, \cdot)$ with kernel $K(\cdot) \geq 0,$ $\int_{\mathbb{R}} K(s)ds =1$. The restrictions $K(s), s \geq 0,$ and $K(s), s \leq 0,$ are responsible for interactions of an individual with his left and right neighbors, respectively. We show that these two parts of $K$ play quite different roles as for the existence and uniqueness of traveling fronts to the KPP-Fisher equation. In particular, if the left interaction is dominant, the uniqueness of fronts can be proved, while the dominance of the right interaction can induce the co-existence of monotone and oscillating fronts. We also present a short proof of the existence of traveling waves without assuming various technical restrictions usually imposed on $K$.

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