arXiv subjects

Qinghui Liu

Publications and source records attributed to Qinghui Liu.

42 records · Page 3Linked to original sources

arXiv2016

"Mixed spectral nature" of Thue--Morse Hamiltonian

We find three dense subsets $Σ_I,Σ_{II}$ and $Σ_{III}$ of the spectrum of the Thue-Morse Hamiltonian, such that each energy in $Σ_I$ is extended, each energy in $Σ_{II}$ is pseudo-localized and each energy in $Σ_{III}$ is one-sided pseudo-localized. We also obtain exact estimations on the norm of the transfer matrices and the norm of the formal solutions for these energies. Especially, for $E\in Σ_{II}\cupΣ_{III}, $ the norms of the transfer matrices behave like $$ e^{c_1γ\sqrt{n}}\le\|T_{n}(E)\|\le e^{c_2γ\sqrt{n}}. $$ The local dimensions of the spectral measure on these subsets are also studied. The local dimension is $0$ for energy in $Σ_{II}$ and is larger than $1$ for energy in $Σ_{I}\cupΣ_{III}.$ In summary, the Thue-Morse Hamiltonian exhibits "mixed spectral nature".

math-ph↗

arXiv2015

Embedding of Hypercube into Cylinder

Task mapping in modern high performance parallel computers can be modeled as a graph embedding problem, which simulates the mapping as embedding one graph into another and try to find the minimum wirelength for the mapping. Though embedding problems have been considered for several regular graphs, such as hypercubes into grids, binary trees into grids, et al, it is still an open problem for hypercubes into cylinders. In this paper, we consider the problem of embedding hypercubes into cylinders to minimize the wirelength. We obtain the exact wirelength formula of embedding hypercube $Q^r$ into cylinder $C_{2^3}\times P_{2^{r-3}}$ with $r\ge3$.

cs.GR↗

arXiv2014

On the Hausdorff dimension of the spectrum of Thue-Morse Hamiltonian

We show that the Hausdorff dimension of the spectrum of the Thue-Morse Hamiltonian has a common positive lower bound for all coupling.

math.DS↗

arXiv2014

The Chinese space millimeter-wavelength VLBI array - a step toward imaging the most compact astronomical objects

The Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences (CAS) is studying a space VLBI (Very Long Baseline Interferometer) program. The ultimate objective of the program is to image the immediate vicinity of the supermassive black holes (SMBHs) in the hearts of galaxies with a space-based VLBI array working at sub-millimeter wavelengths and to gain ultrahigh angular resolution. To achieve this ambitious goal, the mission plan is divided into three stages. The first phase of the program is called Space Millimeter-wavelength VLBI Array (SMVA) consisting of two satellites, each carrying a 10-m diameter radio telescope into elliptical orbits with an apogee height of 60000 km and a perigee height of 1200 km. The VLBI telescopes in space will work at three frequency bands, 43, 22 and 8 GHz. The 43- and 22-GHz bands will be equipped with cryogenic receivers. The space telescopes, observing together with ground-based radio telescopes, enable the highest angular resolution of 20 micro-arcsecond ($μ$as) at 43 GHz. The SMVA is expected to conduct a broad range of high-resolution observational research, e.g. imaging the shadow (dark region) of the supermassive black hole in the heart of the galaxy M87 for the first time, studying the kinematics of water megamasers surrounding the SMBHs, and exploring the power source of active galactic nuclei. Pre-research funding has been granted by the CAS in October 2012, to support scientific and technical feasibility studies. These studies also include the manufacturing of a prototype of the deployable 10-m space-based telescope and a 22-GHz receiver. Here we report on the latest progress of the SMVA project.

astro-ph.IM↗

arXiv2014

Iteration of polynomial pair under Thue-Morse dynamic

We study the behavior of a polynomial sequence which is defined by iterating a polynomial pair under Thue-Morse dynamic. We show that in suitable sense, the sequence will behave like $\{2\cos 2^nx: n\ge 1\}$. Basing on this property we can show that the Hausdorff dimension of the spectrum of the Thue-Morse Hamiltonian has a common positive lower bound for all coupling.

math.DS↗

arXiv2013

The fractal dimensions of the spectrum of Sturm Hamiltonian

Let $α\in(0,1)$ be irrational and $[0;a_1,a_2,\cdots]$ be the continued fraction expansion of $α$. Let $H_{α,V}$ be the Sturm Hamiltonian with frequency $α$ and coupling $V$, $Σ_{α,V}$ be the spectrum of $H_{α,V}$. The fractal dimensions of the spectrum have been determined by Fan, Liu and Wen (Erg. Th. Dyn. Sys.,2011) when $\{a_n\}_{n\ge1}$ is bounded. The present paper will treat the most difficult case, i.e, $\{a_n\}_{n\ge1}$ is unbounded. We prove that for $V\ge24$, $$ \dim_H\ Σ_{α,V}=s_*(V)\ \ \ \text{and}\ \ \ \bar{\dim}_B\ Σ_{α,V}=s^*(V), $$ where $s_*(V)$ and $s^*(V)$ are lower and upper pre-dimensions respectively. By this result, we determine the fractal dimensions of the spectrums for all Sturm Hamiltonians. We also show the following results: $s_*(V)$ and $s^*(V)$ are Lipschitz continuous on any bounded interval of $[24,\infty)$; the limits $s_*(V)\ln V$ and $s^*(V)\ln V$ exist as $V$ tend to infinity, and the limits are constants only depending on $α$; $s^\ast(V)=1$ if and only if $\limsup_{n\to\infty}(a_1\cdots a_n)^{1/n}=\infty,$ which can be compared with the fact: $s_\ast(V)=1$ if and only if $\liminf_{n\to\infty}(a_1\cdots a_n)^{1/n}=\infty$(Liu and Wen, Potential anal. 2004).

math-ph↗