A pointwise cubic average for two commuting transformations

Huang, Shao and Ye recently studied pointwise multiple averages by using suitable topological models. Using a notion of dynamical cubes introduced by the authors, the Huang-Shao-Ye technique and the Host machinery of magic systems, we prove that for a system $(X,\mu,S,T)$ with commuting transformations $S$ and $T$, the average $$\frac{1}{N^2} \sum_{i,j=0}^{N-1} f_0(S^i x)f_1(T^j x)f_2(S^i T^j x)$$ converges a.e. as $N$ goes to infinity for any $f_1,f_2,f_3\in L^{\infty}(\mu)$

PHONON COUPLING AND PHOTOIONIZATION CROSS-SECTIONS IN SEMICONDUCTORS

The coupling to lattice vibrations affects the photoionisation spectra of defects in semiconductors. This is especially important for deep defects. The effects are characterised mainly by a Huang-Rhys factor S0 and by a spectral moment. These are calculated for a variety of electron-photon coupling mechanisms as a function of the observable ionisation energy EI rather than the unobservable effective radius used by previous workers. For Frohlich coupling a good approximation for the Huang-Rhys factor is S0(x)/S0(0)=X/ square root ((5+x)/6) with x=EI/(effective Ryd for purely hydrogenic centre)

Comment on ``Periodic wave functions and number of extended states in random dimer systems'

There are no periodic wave-functions in the RDM but close to the critical energies there exist periodic envelopes. These envelopes are given by the non-disordered properties of the system.Comment: RevTex file, 1 page, Comment X. Huang, X. Wu and C. Gong, Phys. Rev. B 55, 11018 (1997

Almost periodic solutions for an asymmetric oscillation

In this paper we study the dynamical behaviour of the differential equation \begin{equation*} x''+ax^+ -bx^-=f(t), \end{equation*} where $x^+=\max\{x,0\}$,\ $x^-=\max\{-x,0\}$, $a$ and $b$ are two different positive constants, $f(t)$ is a real analytic almost periodic function. For this purpose, firstly, we have to establish some variants of the invariant curve theorem of planar almost periodic mappings, which was proved recently by the authors (see \cite{Huang}).\ Then we will discuss the existence of almost periodic solutions and the boundedness of all solutions for the above asymmetric oscillation.Comment: arXiv admin note: substantial text overlap with arXiv:1606.0893

Spatial ergodicity and central limit theorems for parabolic Anderson model with delta initial condition

Let $\{u(t\,, x)\}_{t >0, x \in\mathbb{R}}$ denote the solution to the parabolic Anderson model with initial condition $\delta_0$ and driven by space-time white noise on $\mathbb{R}_+\times\mathbb{R}$, and let $p_t(x):= (2\pi t)^{-1/2}\exp\{-x^2/(2t)\}$ denote the standard Gaussian heat kernel on the line. We use a non-trivial adaptation of the methods in our companion papers \cite{CKNP,CKNP_b} in order to prove that the random field $x\mapsto u(t\,,x)/p_t(x)$ is ergodic for every $t >0$. And we establish an associated quantitative central limit theorem following the approach based on the Malliavin-Stein method introduced in Huang, Nualart, and Viitasaari \cite{HNV2018}