Ergodic Invariant Measure Research Articles

Proofs of ergodicity of piecewise Möbius interval maps using planar extensions

We give two results for deducing dynamical properties of piecewise Möbius interval maps from their related planar extensions. First, eventual expansivity and the existence of an ergodic invariant probability measure equivalent to Lebesgue measure both follow from mild finiteness conditions on the planar extension along with a new property “bounded non-full range” used to relax traditional Markov conditions. Second, the “quilting” operation to appropriately nearby planar systems, introduced by Kraaikamp and co-authors, can be used to prove several key dynamical properties of a piecewise Möbius interval map. As a proof of concept, we apply these results to recover known results on the well-studied Nakada α-continued fractions; we obtain similar results for interval maps derived from an infinite family of non-commensurable Fuchsian groups.

Non-existence of a universal zero-entropy system via generic actions of almost complete growth

Abstract We prove that a generic probability measure-preserving (p.m.p.) action of a countable amenable group G has scaling entropy that cannot be dominated by a given rate of growth. As a corollary, we obtain that there does not exist a topological action of G for which the set of ergodic invariant measures coincides with the set of all ergodic p.m.p. G-systems of entropy zero. We also prove that a generic action of a residually finite amenable group has scaling entropy that cannot be bounded from below by a given sequence. In addition, we show an example of an amenable group that has such a lower bound for every free p.m.p. action.

Dynamical Analysis of Stochastic Predator-prey Model with Scavenger

In this paper, we studied the dynamic properties of predator-prey and scavenger three species system by using ergodic invariant measures. Pengyu Ma. find the five points of dynamical bifurcation of the stochastic model, which happened between extinction and survival of each species. Environmental noise was added and proved by the fact that driving force produced by environmental noise influence the system and it was find that system may extinct or partially extinct. Here, we have analysed the stochastic bifurcation phenomena of the prey-predator with scavenger system from the nature of dynamic bifurcation. The phase plots and time diagram plotted for the different values of parameters. We have verified all the results by numerical simulations.

Stability and dynamical bifurcation of a stochastic regime-switching predator–prey model

This paper considers a stochastic regime-switching predator–prey system with general functional response. We show that the system exactly possesses two dynamical bifurcation points (DBPs), and the expressions of these DBPs are given explicitly. In addition, we provide the sharp sufficient criteria under which the system admits a unique ergodic invariant measure (UEIM), and show that the transition function of the solution of the system exponentially converges to the UEIM under the total variation norm. The findings show that the stability and dynamical bifurcation of the system have close relationships with the random perturbations. Additionally, the main findings are applied to several special cases, and a number of recent reports are improved.

A stochastic framework for evaluating CAR T cell therapy efficacy and variability

Based on a deterministic and stochastic process hybrid model, we use white noises to account for patient variabilities in treatment outcomes, use a hyperparameter to represent patient heterogeneity in a cohort, and construct a stochastic model in terms of Ito stochastic differential equations for testing the efficacy of three different treatment protocols in CAR T cell therapy. The stochastic model has three ergodic invariant measures which correspond to three unstable equilibrium solutions of the deterministic system, while the ergodic invariant measures are attractors under some conditions for tumor growth. As the stable dynamics of the stochastic system reflects long-term outcomes of the therapy, the transient dynamics provide chances of cure in short-term. Two stopping times, the time to cure and time to progress, allow us to conduct numerical simulations with three different protocols of CAR T cell treatment through the transient dynamics of the stochastic model. The probability distributions of the time to cure and time to progress present outcome details of different protocols, which are significant for current clinical study of CAR T cell therapy.

Geometric interpretation of the entropy of so c systems

We consider a geometric approach to the notion of metric entropy. We justify the possibility of this approach for the class of Borel invariant ergodic probability measures on so c systems, which is the rst result of such generality for non-Markovian systems.

Amenable wreath products with non almost finite actions of mean dimension zero

Almost finiteness was introduced in the seminal work of Kerr [J. Eur. Math. Soc. (JEMS) 22 (2020), pp. 3697–3745] as an dynamical analogue of Z \mathcal {Z} -stability in the Toms-Winter conjecture. In this article, we provide the first examples of minimal, topologically free actions of amenable groups that have mean dimension zero but are not almost finite. More precisely, we prove that there exists an infinite family of amenable wreath products that admit topologically free, minimal profinite actions on the Cantor space which fail to be almost finite. Furthermore, these actions have dynamical comparison. This intriguing new phenomenon shows that Kerr’s dynamical analogue of Toms-Winter conjecture fails for minimal, topologically free actions of amenable groups. The notion of allosteric group holds a significant position in our study. A group is allosteric if it admits a minimal action on a compact space with an invariant ergodic probability measure that is topologically free but not essentially free. We study allostery of wreath products and provide the first examples of allosteric amenable groups.

Invariant measures for stochastic conservation laws on the line

We consider a stochastic conservation law on the line with solution-dependent diffusivity, a super-linear, sub-quadratic Hamiltonian, and smooth, spatially-homogeneous kick-type random forcing. We show that this Markov process admits a unique ergodic spatially-homogeneous invariant measure for each mean in a non-explicit unbounded set. This generalises previous work on the stochastic Burgers equation.

Topological chaos and statistical triviality

While transferring one flow ϕ with fixed points homeomorphically to its equivalent flow ψ, we show that positive topological entropy degenerates to zero (such degeneracy happens for equivalent continuous flows [3] and equivalent differential flows [6]) if and only if all ergodic invariant measures with positive measure-theoretic entropy degenerate to fixed points. Whenever ϕ is assumed to be topological transitive, the measure degeneracy implies that the resulted equivalent flow ψ is topologically chaotic but statistically trivial, meaning that all ergodic invariant measures are supported on fixed points. Using different approaches in different areas people constructed examples of topological chaotic but statistical trivial systems, see [3] for C0 flows, see [6] for Cr, r≥1, flows, see [1][11] for C0 homeomorphisms, see time one map in [6] for Cr, r≥1 diffeomorphisms. We point out it is non-hyperbolic singularity causes the degeneracy while changing one flow equivalently to another.

Global martingale and pathwise solutions and infinite regularity of invariant measures for a stochastic modified Swift–Hohenberg equation

We consider a 2D stochastic modified Swift–Hohenberg equations with multiplicative noise and periodic boundary. First, we establish the existence of local and global martingale and pathwise solutions in the regular Sobolev space for each . Associated with the unique global pathwise solution, we obtain a Markovian transition semigroup. Then, we show the existence of invariant measures and ergodic invariant measures for this Markovian semigroup on . At last, we improve the regularity of the obtained invariant measures to . With appropriate conditions on the diffusion coefficient, we can deduce the infinite regularity of the invariant measures, which was conjectured by Glatt-Holtz et al in their situation (2014 J. Math. Phys. 55 277–304).

On the number of ergodic physical/SRB measures of singular-hyperbolic attracting sets

It is known that sectional-hyperbolic attracting sets, for a C2 flow on a finite dimensional compact manifold, have at most finitely many ergodic physical invariant probability measures. We prove an upper bound for the number of distinct ergodic physical measures supported on a connected singular-hyperbolic attracting set for a 3-flow. This bound depends only on the number of Lorenz-like equilibria contained in the attracting set, as a consequence of the property that, for any physical measure whose support contains a singularity (which is necessarily a Lorenz-like singularity), almost every unstable manifold crosses the stable manifold of the singularity transversely. Examples of singular-hyperbolic attracting sets are provided showing that the bound is sharp.

Variational principles for topological pressures on subsets

In this paper, we investigate the relations between various types of topological pressures and different versions of measure-theoretical pressures. We extend Feng–Huang’s variational principle for packing entropy to packing pressure and obtain two new variational principles for Pesin–Pitskel and packing pressures respectively. We show that various types of Katok pressures for an ergodic measure with respect to a potential function are equal to the sum of measure-theoretic entropy of this measure and the integral of the potential function. Moreover, we obtain Billingsley type theorem for packing pressure, which indicates that packing pressure can be determined by measure-theoretic upper local pressure of measures, and a variational principle for packing pressure of the set of generic points for any invariant ergodic Borel probability measure.

Thresholds and critical states for a stochastic predator–prey model with mixed functional responses

In this paper, we are committed to the study of thresholds (between persistence and extinction) for all the species in a stochastic predator–prey model, which takes both Beddington–DeAngelis and Holling-II functional responses. One interesting thing we find is that the ith Lyapunov exponent defined for an ergodic invariant measure may just happen to be the threshold for the ith species. Furthermore, we discuss the priority levels among multiple thresholds for the same species, which is a novel feature of this paper. A brief summary of priority level is that, Lyapunov exponent for a high-dimensional measure has higher priority than that of a low-dimensional measure. At the end of the paper, we analyze dynamic properties for some critical states.

Characters of algebraic groups over number fields

Let k be a number field, \mathbf{G} an algebraic group defined over k , and \mathbf{G}(k) the group of k -rational points in \mathbf{G} . We determine the set of functions on \mathbf{G}(k) which are of positive type and conjugation invariant, under the assumption that \mathbf{G}(k) is generated by its unipotent elements. An essential step in the proof is the classification of the \mathbf{G}(k) -invariant ergodic probability measures on an adelic solenoid naturally associated to \mathbf{G}(k) . This last result is deduced from Ratner’s measure rigidity theorem for homogeneous spaces of S -adic Lie groups; this appears to be the first application of Ratner’s theorems in the context of operator algebras.

Central measures of continuous graded graphs: the case of distinct frequencies

We define a class of continuous graded graphs similar to the graph of Gelfand–Tsetlin patterns, and describe the set of all ergodic central measures of discrete type on the path spaces of such graphs. The main observation is that an ergodic central measure on a subgraph of a Pascal-type graph can often be obtained as the restriction of the standard Bernoulli measure to the path space of the subgraph. This observation dramatically changes the approach to finding central measures also on discrete graphs, such as the famous Young graph. The simplest example of this type is given by the theorem on the weak limits of normalized Lebesgue measures on simplices; these are the so-called Cesàro measures, which are concentrated on the sequences with prescribed Cesàro limits (this limit parametrizes the corresponding measure). More complicated examples are the graphs of continuous Young diagrams with fixed number of rows and the graphs of spectra of infinite Hermitian matrices of finite rank. We prove existence and uniqueness theorems for ergodic central measures and describe their structure. In particular, our results (1) give a new spectral description of the so-called infinite-dimensional Wishart measures (in Biometrika 20A(1–2):32–52, 1928)—ergodic unitarily invariant measures of discrete type on the set of infinite Hermitian matrices; (2) describe the structure of continuous analogs of measures on discrete graded graphs. New problems and connections which appear are to be considered in new publications.

Ergodic invariant measures on the space of geodesic currents

Let S be a compact, connected, oriented surface, possibly with boundary, of negative Euler characteristic. In this article we extend Lindenstrauss–Mirzakhani’s and Hamenstädt’s classification of locally finite mapping class group invariant ergodic measures on the space of measured laminations ℳℒ(S) to the space of geodesic currents 𝒞(S), and we discuss the homogeneous case. Moreover, we extend Lindenstrauss–Mirzakhani’s classification of orbit closures to 𝒞(S). Our argument relies on their results and on the decomposition of a current into a sum of three currents with isotopically disjoint supports: a measured lamination without closed leaves, a simple multi-curve and a current that binds its hull.

Non-existence of a universal zero entropy system for non-periodic amenable group actions

Let G be a non-periodic amenable group. We prove that there does not exist a topological action of G for which the set of ergodic invariant measures coincides with the set of all ergodic measure-theoretic G-systems of entropy zero. Previously J. Serafin, answering a question by B. Weiss, proved the same for G = ℤ.

Continuity properties of Lyapunov exponents for surface diffeomorphisms

We study the entropy and Lyapunov exponents of invariant measures $\mu$ for smooth surface diffeomorphisms $f$, as functions of $(f,\mu)$. The main result is an inequality relating the discontinuities of these functions. One consequence is that for a $C^\infty$ surface diffeomorphisms, on any set of ergodic measures with entropy bounded away from zero, continuity of the entropy implies continuity of the exponents. Another consequence is the upper semi-continuity of the Hausdorff dimension on the set of ergodic invariant measures with entropy bounded away from zero. We also obtain a new criterion for the existence of SRB measures with positive entropy.

Hopf bifurcation without parameters in deterministic and stochastic modeling of cancer virotherapy, part II

In part II, we analyze our stochastic model which incorporates microenvironmental noises and uncertainties related to immune responses. Outcomes of the therapy in our model are largely determined by the infectivity constant, the infection value, and stochastic relative immune clearance rates. The infection value is a universal critical value for immune-free ergodic invariant probability measures and persistence in all cases. Asymptotic behaviors of the stochastic model are similar to those of its deterministic counterpart. Our stochastic model displays an interesting dynamical behavior, stochastic Hopf bifurcation without parameters, which is a new phenomenon. We perform numerical study to demonstrate how stochastic Hopf bifurcation without parameters occurs. In addition, we give biological implications about our analytical results in stochastic setting versus deterministic setting.

Dimension estimates for iterated function systems and repellers. Part I

AbstractThis is the first paper in a two-part series containing some results on dimension estimates for $C^1$ iterated function systems and repellers. In this part, we prove that the upper box-counting dimension of the attractor of any $C^1$ iterated function system (IFS) on ${\Bbb R}^d$ is bounded above by its singularity dimension, and the upper packing dimension of any ergodic invariant measure associated with this IFS is bounded above by its Lyapunov dimension. Similar results are obtained for the repellers for $C^1$ expanding maps on Riemannian manifolds.