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Dun Zhou

Publications and source records attributed to Dun Zhou.

12 recordsLinked to original sources
arXiv2026

Statistical behavior of systems with nested invariant cones

Nested invariant cones (NICs) encode hierarchical order and oscillation structures in many finite and infinite dimensional dynamical systems. We investigate how this hierarchy constrains the Birkhoff center and the supports of invariant probability measures. For eventually compact, dissipative semiflows that are uniformly eventually strongly monotone with respect to NICs, we prove that every connected component $B$ of the Birkhoff center lies in a single cone layer: there exists $j>0$ such that $B$ is unordered with respect to all lower-level cones and strongly ordered with respect to all cones at level $j$ or higher. The same conclusion holds for every connected component of the support of an invariant probability measure. Under an additional transversality condition involving a codimension-$d$ linear subspace, each such component admits a homeomorphic embedding into $\mathbb R^d$. If $d=1$ or $2$ and the restriction of the semiflow to its global attractor extends to a flow, then the system has zero topological entropy, independently of the dimension of the original phase space. We apply the theory to bidirectional cyclic feedback systems and scalar parabolic equations on the circle. In the parabolic case, the natural infinite family of zero-number NICs fails to be uniformly eventually strongly monotone, even for the heat equation; we overcome this obstruction by constructing a finite family of perturbed NICs. In both applications, every connected component of the Birkhoff center admits a planar embedding, and the topological entropy is zero.

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arXiv2026

Robust dynamics of non-autonomous systems with nested invariant cone structures

We develop a perturbation theory for skew-product semiflows with nested invariant cone (NIC) structures over compact almost periodic minimal flows. The theory describes how the restrictions imposed by these structures on asymptotic dynamics persist under small $C^1$ perturbations. We first establish a trichotomy for differences of perturbed trajectories: finite-time coincidence, exponential contraction outside the terminal cone, or eventual separation within a fixed cone layer. On compact invariant sets near the reference set, the perturbed semiflow extends to a flow. Under a transversality condition, compact invariant sets whose orbit differences remain in fixed cone layers admit finite-dimensional fibre realizations over the original base flow. In the codimension-one case, every compact minimal set in the perturbative neighborhood is an almost $1$-cover of the base. For precompact positive orbits whose $ω$-limit sets lie in this neighborhood, we prove that each $ω$-limit set contains at most two minimal sets and classify the remaining orbits by their forward and backward limit sets. Applications include nonlocal and chemotaxis-type perturbations of scalar parabolic equations with homogeneous Neumann boundary conditions and perturbations of competitive--cooperative tridiagonal systems. Under dissipativity assumptions, these applications give global conclusions for almost periodically forced equations, including perturbations that destroy the original zero-number or sign-variation mechanism.

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arXiv2025

Structural stability for the bidirectional cyclic negative feedback systems

The present paper investigates the structural stability of bidirectional cyclic negative feedback systems. To address this, we develop a generalized Floquet theory and construct nested invariant cones for the systems. Subsequently, we demonstrate that the Poincaré-Bendixson property for the limit set persists under $C^1$-perturbations. By applying the generalized Floquet theory and the nested invariant cones, we establish that the stable and unstable manifolds of any two connecting hyperbolic critical elements intersect transversally, with the exception of two hyperbolic equilibria possessing the same odd Morse index. Next, we prove the generic hyperbolicity of critical elements using the Sard-Smale theorem. Furthermore, by formulating the transversality condition as a functional constraint, we generically preclude connecting orbits between hyperbolic equilibrium points with the same odd Morse index, thereby establishing the generic Kupka-Smale property. Finally, under dissipative assumptions, we show that the system generically exhibits the Morse-Smale property. Our findings characterize the stability of bidirectional cyclic negative feedback systems in two distinct manners: $C^1$- small perturbations of the system do not alter the asymptotic behavior of orbits; from a topological perspective, generic vector fields in bidirectional cyclic negative feedback systems are structurally stable.

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arXiv2024

Dynamics of a class of time-period strongly 2-cooperative system: integer-valued Lyapunov function and embedding property of limit sets

We construct an integer-valued Lyapunov function $σ(\cdot)$ for generalized negative cyclic feedback system; and prove that $σ(\cdot)$ on any $ω$-limit set which generated by Poincaré mapping of bounded solution of such strongly $2$-cooperative system is constant. Therefore, the $ω$-limit can be continuously embedded into a compact subset of a two-dimensional plane. Finally, a dissipative condition is given to ensure that all orbits of such system are bounded.

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arXiv2023

The Morse Smale property for time-periodic scalar reaction-diffusion equation on the circle

\begin{abstract} We study the Morse-Smale property for the following scalar semilinear parabolic equation on the circle $S^1$, \begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in S^{1}=\mathbb{R}/2π\mathbb{Z}, \end{equation*} where $f$ is a $C^2$ function and $T$-periodic in $t$. Assume that the equation admits a compact global attractor $\mathcal{A}$ and let $P$ be the Poincaré map of this equation. We exclude homoclinic connection for hyperbolic fixed points of $P$ and prove that stable and unstable manifolds for any two heteroclinic hyperbolic fixed points of $P$ intersect transversely. Further, this equation admits the Morse-Smale property provided that all $ω$-limit sets (in the case $f(t,u,u_x)=f(t,u,-u_x)$, the $ω$-limit set is just a fixed point) of the corresponding Poincaré map are hyperbolic. \end{abstract}

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arXiv2020

Non-wandering points for autonomous/periodic parabolic equations on the circle

We study the properties of non-wandering points of the following scalar reaction-diffusion equation on the circle $S^1$, \begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in S^{1}=\mathbb{R}/2π\mathbb{Z}, \end{equation*} where $f$ is independent of $t$ or $T$-periodic in $t$. Assume that the equation admits a compact global attractor. It is proved that, any non-wandering point is a limit point of the system (that is, it is a point in some $ω$-limit set). More precisely, in the autonomous case, it is proved that any non-wandering point is either a fixed point or generates a rotating wave on the circle. In the periodic case, it is proved that any non-wandering point is a periodic point or generates a rotating wave on a torus. In particular, if $f(t,u,-u_x)=f(t,u,u_x)$, then any non-wandering point is a fixed point in the autonomous case, and is a periodic point in the periodic case.

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arXiv2020

Almost automorphically forced flows on $S^1$ or $\mathbb{R}$ in one-dimensional almost periodic semilinear heat equations

In this paper, we consider the asymptotic dynamics of the skew-product semiflow generated by the following time almost-periodically forced scalar reaction-diffusion equation \begin{equation}\label{eq0} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\, 0<x<L \end{equation} with periodic boundary condition \begin{equation} \label{bdc1} u(t,0)=u(t,L),\quad u_x(t,0)=u_x(t,L), \end{equation} where $f$ is uniformly almost periodic in $t$. In particular, we study the topological structure of the limit sets of the skew-product semiflow. It is proved that any compact minimal invariant set (throughout this paper, we refer to it as a minimal set) can be residually embedded into an invariant set of some almost automorphically-forced flow on a circle $S^1=\mathbb{R}/L\mathbb{Z}$. Particularly, if $f(t,u,p)=f(t,u,-p)$, then the flow on a minimal set topologically conjugates to an almost periodically-forced minimal flow on $\mathbb{R}$. Moreover, it is proved that the $ω$-limit set of any bounded orbit contains at most two minimal sets that cannot be obtained from each other by phase translation. In addition, we further consider the asymptotic dynamics of the skew-product semiflow generated by \eqref{eq0} with Neumann boundary condition \begin{equation*} \label{bcd2} u_x(t,0)=u_x(t,L)=0, \end{equation*} or Dirichlet boundary condition \begin{equation*}\label{bdc3} u(t,0)=u(t,L)=0. \end{equation*} Under certain direct assumptions on $f$, it is proved in this paper that the flow on any minimal set of \eqref{eq0}, with Neumann boundary condition or Dirichlet boundary condition, topologically conjugates to an almost periodically-forced minimal flow on $\mathbb{R}$. Finally, a counterexample is given to show that even for quasi-periodic equations, the results we obtain here cannot be further improved in general.

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arXiv2017

Almost Automorphically and Almost Periodically Forced Circle Flows of Almost Periodic Parabolic Equations on S^1

We consider the skew-product semiflow which is generated by a scalar reaction-diffusion equation \begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in S^{1}=\mathbb{R}/2π\mathbb{Z}, \end{equation*} where $f$ is uniformly almost periodic in $t$. The structure of the minimal set $M$ is thoroughly investigated under the assumption that the center space $V^c(M)$ associated with $M$ is no more than $2$-dimensional. Such situation naturally occurs while, for instance, $M$ is hyperbolic or uniquely ergodic. It is shown in this paper that $M$ is a $1$-cover of the hull $H(f)$ provided that $M$ is hyperbolic (equivalently, ${\rm dim}V^c(M)=0$). If ${\rm dim}V^c(M)=1$ (resp. ${\rm dim}V^c(M)=2$ with ${\rm dim}V^u(M)$ being odd), then either $M$ is an almost $1$-cover of $H(f)$ and topologically conjugate to a minimal flow in $\mathbb{R}\times H(f)$; or $M$ can be (resp. residually) embedded into an almost periodically (resp. almost automorphically) forced circle-flow $S^1\times H(f)$. When $f(t,u,u_x)=f(t,u,-u_x)$ (which includes the case $f=f(t,u)$), it is proved that any minimal set $M$ is an almost $1$-cover of $H(f)$. In particular, any hyperbolic minimal set $M$ is a $1$-cover of $H(f)$. Furthermore, if ${\rm dim}V^c(M)=1$, then $M$ is either a $1$-cover of $H(f)$ or is topologically conjugate to a minimal flow in $\mathbb{R}\times H(f)$. For the general spatially-dependent nonlinearity $f=f(t,x,u,u_{x})$, we show that any stable or linearly stable minimal invariant set $M$ is residually embedded into $\mathbb{R}^2\times H(f)$.

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arXiv2017

Asymptotic behavior of semilinear parabolic equations on the circle with time almost-periodic/recurrent dependence

We study topological structure of the $ω$-limit sets of the skew-product semiflow generated by the following scalar reaction-diffusion equation \begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in S^{1}=\mathbb{R}/2π\mathbb{Z}, \end{equation*} where $f(t,u,u_x)$ is $C^2$-admissible with time-recurrent structure including almost-periodicity and almost-automorphy. Contrary to the time-periodic cases (for which any $ω$-limit set can be imbedded into a periodically forced circle flow), it is shown that one cannot expect that any $ω$-limit set can be imbedded into an almost-periodically forced circle flow even if $f$ is uniformly almost-periodic in $t$. More precisely, we prove that, for a given $ω$-limit set $Ω$, if ${\rm dim}V^c(Ω)\leq 1$ ($V^c(Ω)$ is the center space associated with $Ω$), then $Ω$ is either spatially-homogeneous or spatially-inhomogeneous; and moreover, any spatially-inhomogeneous $Ω$ can be imbedded into a time-recurrently forced circle flow (resp. imbedded into an almost periodically-forced circle flow if $f$ is uniformly almost-periodic in $t$). On the other hand, when ${\rm dim}V^c(Ω>1$, it is pointed out that the above embedding property cannot hold anymore. Furthermore, we also show the new phenomena of the residual imbedding into a time-recurrently forced circle flow (resp. into an almost automorphically-forced circle flow if $f$ is uniformly almost-periodic in $t$) provided that $\dim V^c(Ω)=2$ and $\dim V^u(Ω)$ is odd. All these results reveal that for such system there are essential differences between time-periodic cases and non-periodic cases.

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arXiv2016

Structure of $ω$-limit Sets for Almost-periodic Parabolic Equations on $S^1$ with Reflection Symmetry

The structure of the $ω$-limit sets is thoroughly investigated for the skew-product semiflow which is generated by a scalar reaction-diffusion equation \begin{equation*} u_{t}=u_{xx}+f(t,u,u_{x}),\,\,t>0,\,x\in S^{1}=\mathbb{R}/2π\mathbb{Z}, \end{equation*} where $f$ is uniformly almost periodic in $t$ and satisfies $f(t,u,u_x)=f(t,u,-u_x)$. We show that any $ω$-limit set $Ω$ contains at most two minimal sets. Moreover, any hyperbolic $ω$-limit set $Ω$ is a spatially-homogeneous $1$-cover of hull $H(f)$. When $\dim V^c(Ω)=1$ ($V^c(Ω)$ is the center space associated with $Ω$), it is proved that either $Ω$ is a spatially-homogeneous, or $Ω$ is a spatially-inhomogeneous $1$-cover of $H(f)$.

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arXiv2014

Transversality for Cyclic Negative Feedback Systems

Transversality of stable and unstable manifolds of hyperbolic periodic trajectories is proved for monotone cyclic systems with negative feedback. Such systems in general are not in the category of monotone dynamical systems in the sense of Hirsch. Our main tool utilized in the proofs is the so-called cone of high rank. We further show that stable and unstable manifolds between a hyperbolic equilibrium and a hyperbolic periodic trajectory, or between two hyperbolic equilibria with different dimensional unstable manifolds also intersect transversely.

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