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1. Phase mixing for solutions to 1D transport equation in a confining potential

   https://doi.org/10.3934/krm.2022002  

   Chaturvedi, Sanchit ; Luk, Jonathan ( January 2022 , Kinetic and Related Models)

   Consider the linear transport equation in 1D under an external confining potential \begin{document}$ \Phi $\end{document}:

   \begin{document}$ \begin{equation*} {\partial}_t f + v {\partial}_x f - {\partial}_x \Phi {\partial}_v f = 0. \end{equation*} $\end{document}

   For \begin{document}$ \Phi = \frac {x^2}2 + \frac { \varepsilon x^4}2 $\end{document} (with \begin{document}$ \varepsilon >0 $\end{document} small), we prove phase mixing and quantitative decay estimates for \begin{document}$ {\partial}_t \varphi : = - \Delta^{-1} \int_{ \mathbb{R}} {\partial}_t f \, \mathrm{d} v $\end{document}, with an inverse polynomial decay rate \begin{document}$ O({\langle} t{\rangle}^{-2}) $\end{document}. In the proof, we develop a commuting vector field approach, suitably adapted to this setting. We will explain why we hope this is relevant for the nonlinear stability of the zero solution for the Vlasov–Poisson system in \begin{document}$ 1 $\end{document}D under the external potential \begin{document}$ \Phi $\end{document}.

    

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2. Common preperiodic points for quadratic polynomials

   https://doi.org/10.3934/jmd.2022012  

   DeMarco, Laura ; Krieger, Holly ; Ye, Hexi ( January 2022 , Journal of Modern Dynamics)

   Let \begin{document}$ f_c(z) = z^2+c $\end{document} for \begin{document}$ c \in {\mathbb C} $\end{document}. We show there exists a uniform upper bound on the number of points in \begin{document}$ {\mathbb P}^1( {\mathbb C}) $\end{document} that can be preperiodic for both \begin{document}$ f_{c_1} $\end{document} and \begin{document}$ f_{c_2} $\end{document}, for any pair \begin{document}$ c_1\not = c_2 $\end{document} in \begin{document}$ {\mathbb C} $\end{document}. The proof combines arithmetic ingredients with complex-analytic: we estimate an adelic energy pairing when the parameters lie in \begin{document}$ \overline{\mathbb{Q}} $\end{document}, building on the quantitative arithmetic equidistribution theorem of Favre and Rivera-Letelier, and we use distortion theorems in complex analysis to control the size of the intersection of distinct Julia sets. The proofs are effective, and we provide explicit constants for each of the results.

    

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3. Existence of global weak solutions of $ p $-Navier-Stokes equations

   https://doi.org/10.3934/dcdsb.2021051  

   Liu, Jian-Guo ; Zhang, Zhaoyun ( January 2022 , Discrete & Continuous Dynamical Systems - B)

   This paper investigates the global existence of weak solutions for the incompressible \begin{document}$ p $\end{document}-Navier-Stokes equations in \begin{document}$ \mathbb{R}^d $\end{document} \begin{document}$ (2\leq d\leq p) $\end{document}. The \begin{document}$ p $\end{document}-Navier-Stokes equations are obtained by adding viscosity term to the \begin{document}$ p $\end{document}-Euler equations. The diffusion added is represented by the \begin{document}$ p $\end{document}-Laplacian of velocity and the \begin{document}$ p $\end{document}-Euler equations are derived as the Euler-Lagrange equations for the action represented by the Benamou-Brenier characterization of Wasserstein-\begin{document}$ p $\end{document} distances with constraint density to be characteristic functions.

    

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4. Highly accurate operator factorization methods for the integral fractional Laplacian and its generalization

   https://doi.org/10.3934/dcdss.2022016  

   Wu, Yixuan ; Zhang, Yanzhi ( January 2022 , Discrete & Continuous Dynamical Systems - S)

   In this paper, we propose a new class of operator factorization methods to discretize the integral fractional Laplacian \begin{document}$ (- \Delta)^\frac{{ \alpha}}{{2}} $\end{document} for \begin{document}$ \alpha \in (0, 2) $\end{document}. One main advantage is that our method can easily increase numerical accuracy by using high-degree Lagrange basis functions, but remain its scheme structure and computer implementation unchanged. Moreover, it results in a symmetric (multilevel) Toeplitz differentiation matrix, enabling efficient computation via the fast Fourier transforms. If constant or linear basis functions are used, our method has an accuracy of \begin{document}$ {\mathcal O}(h^2) $\end{document}, while \begin{document}$ {\mathcal O}(h^4) $\end{document} for quadratic basis functions with \begin{document}$ h $\end{document} a small mesh size. This accuracy can be achieved for any \begin{document}$ \alpha \in (0, 2) $\end{document} and can be further increased if higher-degree basis functions are chosen. Numerical experiments are provided to approximate the fractional Laplacian and solve the fractional Poisson problems. It shows that if the solution of fractional Poisson problem satisfies \begin{document}$ u \in C^{m, l}(\bar{ \Omega}) $\end{document} for \begin{document}$ m \in {\mathbb N} $\end{document} and \begin{document}$ 0 < l < 1 $\end{document}, our method has an accuracy of \begin{document}$ {\mathcal O}(h^{\min\{m+l, \, 2\}}) $\end{document} for constant and linear basis functions, while \begin{document}$ {\mathcal O}(h^{\min\{m+l, \, 4\}}) $\end{document} for quadratic basis functions. Additionally, our method can be readily applied to approximate the generalized fractional Laplacians with symmetric kernel function, and numerical study on the tempered fractional Poisson problem demonstrates its efficiency.

    

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5. Tail probability estimates of continuous-time simulated annealing processes

   https://doi.org/10.3934/naco.2022015  

   Tang, Wenpin ; Zhou, Xun Yu ( January 2022 , Numerical Algebra, Control and Optimization)

   We study the convergence rate of a continuous-time simulated annealing process \begin{document}$ (X_t; \, t \ge 0) $\end{document} for approximating the global optimum of a given function \begin{document}$ f $\end{document}. We prove that the tail probability \begin{document}$ \mathbb{P}(f(X_t) > \min f +\delta) $\end{document} decays polynomial in time with an appropriately chosen cooling schedule of temperature, and provide an explicit convergence rate through a non-asymptotic bound. Our argument applies recent development of the Eyring-Kramers law on functional inequalities for the Gibbs measure at low temperatures.

    

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