Fractals Everywhere

Abstract

Like every other component of government these days, the U.S. federal statistical system is being reinvented, reengineered, and downsized. At this writing, several bills are before the U.S. Congress to restructure the system, relocate key agencies, and reallocate programs and budgets. Janet L. Norwood, Senior Fellow with The Urban Institute and former Commissioner of Labor Statistics, offers a trenchant commentary on the situation. Norwood identifies serious problems with the U.S. federal statistical system, as it is currently organized, that need to be addressed. At the same time, she notes the grave danger that solutions attempted by the U.S. Congress may make matters worse. She ends with a call to action for those who “care about data quality and who understand the important uses of the government's statistical output.”     

Almost Everywhere Convergent Fourier Series

We study some properties of the logconvex quasi-Banach space QA defined by Arias-de-Reyna and show several applications to convergence of Fourier series. In particular, we describe the Banach envelope of QA and prove that there exists a Lorentz space strictly bigger than the Antonov space in which the almost everywhere convergence of the Fourier series holds. We also give a necessary condition for a Banach rearrangement invariant space X to be contained in QA. As an application, we show that for some classes of Banach spaces there is no the largest Banach space in a given class which is contained in QA.     

Sum of Everywhere Convergent Trigonometric Series

Mathematical Notes -     

Everywhere -repetitive sequences and Sturmian words

Local constraints on an infinite sequence that imply global regularity are of general interest in combinatorics on words. We consider this topic by studying everywhere α-repetitive sequences. Such a sequence is defined by the property that there exists an integer N≥2 such that every length-N factor has a repetition of order α as a prefix. If each repetition is of order strictly larger than α, then the sequence is called everywhere α⁺-repetitive. In both cases, the number of distinct minimal α-repetitions (or α⁺-repetitions) occurring in the sequence is finite.A natural question regarding global regularity is to determine the least number, denoted by M(α), of distinct minimalα-repetitions such that an α-repetitive sequence is not necessarily ultimately periodic. We call the everywhere α-repetitive sequences witnessing this property optimal. In this paper, we study optimal 2-repetitive sequences and optimal 2⁺-repetitive sequences, and show that Sturmian words belong to both classes. We also give a characterization of 2-repetitive sequences and solve the values of M(α) for 1≤α≤15/7.     

Everywhere differentiability of infinity harmonic functions

We show that an infinity harmonic function, that is, a viscosity solution of the nonlinear PDE ${- \Delta_\infty u = -u_{x_i}u_{x_j}u_{x_ix_j} = 0}$ , is everywhere differentiable. Our new innovation is proving the uniqueness of appropriately rescaled blow-up limits around an arbitrary point.     

Furstenberg族与处处混沌及等度连续(英文)

本文引进并研究了Furstenberg族意义下的处处混沌与等度连续的概念.如果一个动力系统是F_1-敏感和F_2-可达的,则称之为(F_1,F_2)-处处混沌的,其中F_1与F_2是Furstenberg族.一个动力系统(X,f)被称为F_1-敏感的,是指存在7>0使得对任意x∈X及x的任意开邻域存在y∈U,有{n∈Z_+:d(f~n(x),f~n(y))>τ}∈F_1成立.一个动力系统(X,f)被称为F_2-可达的,是指对任意的s>O及X的任意非空开集U,V,存在x∈U,y∈V使得{n∈Z_+:d(f~n(x),f~n(y))<ε}∈F_1成立.一个动力系统被称为F-等度连续的,是指对任意的ε>0,存在δ>0,当d(x,y)<δ时有{n∈Z_+:d(f~n(x),f~n(y))<ε}∈F成立,其中F是一个Furstenberg族.     

Everywhere regularity of certain nonlinear diffusion systems

In this paper I discuss nonlinear parabolic systems that are generalizations of scalar diffusion equations. More precisely, I consider systems of the form $$\mathbf{u}_t -\Delta\left[ \mathbf{\nabla}\Phi(\mathbf{u})\right] = 0,$$ where ${\Phi(z)}$ is a strictly convex function. I show that when ${\Phi}$ is a function only of the norm of u, then bounded weak solutions of these parabolic systems are everywhere Hölder continuous and thus everywhere smooth. I also show that the method used to prove this result can be easily adopted to simplify the proof of the result due to Wiegner (Math Ann 292(4):711–727, 1992) on everywhere regularity of bounded weak solutions of strongly coupled parabolic systems.