arXiv subjects

Li Wang

Publications and source records attributed to Li Wang.

At least 613 records · Page 34Linked to original sources

arXiv2011

Downtrack response of differential reader for high density magnetic recording

The downtrack responses of a differential reader to various magnetic patterns have been investigated micromagnetically. The differential signals can well discriminate the "0" and "1" readback bits and the waveforms obtained resemble the counterparts for longitudinal media or for perpendicular media after differentiation. Pulse shapes are found Gaussian. With decreasing head media spacing, free layer thickness, and gap length, PW50 roughly linearly decreases and the maximum signal exponentially increases. These properties, together with small inter-symbol interference, are essential for future high density magnetic recording.

cond-mat.mtrl-sci↗

arXiv2011

Uniformly stable rectangular elements for fourth order elliptic singular perturbation problems

This paper analyzes rectangular finite element methods for fourth order elliptic singular perturbation problems. We show that the non-$C^0$ rectangular Morley element is uniformly convergent in the energy norm with respect to the perturbation parameter. We also propose a $C^0$ extended high order rectangular Morley element and prove the uniform convergence. Finally, we do some numerical experiments to confirm the theoretical results.

math.NA↗

arXiv2011

Nonparametric Additive Model-assisted Estimation for Survey Data

An additive model-assisted nonparametric method is investigated to estimate the finite population totals of massive survey data with the aid of auxiliary information. A class of estimators is proposed to improve the precision of the well known Horvitz-Thompson estimators by combining the spline and local polynomial smoothing methods. These estimators are calibrated, asymptotically design-unbiased, consistent, normal and robust in the sense of asymptotically attaining the Godambe-Joshi lower bound to the anticipated variance. A consistent model selection procedure is further developed to select the significant auxiliary variables. The proposed method is sufficiently fast to analyze large survey data of high dimension within seconds. The performance of the proposed method is assessed empirically via simulation studies.

stat.ME↗

arXiv2010

Graphite Nanoeraser

We present here a method for cleaning intermediate-size (5~50nm) contamination from highly oriented pyrolytic graphite. Electron beam deposition causes a continuous increase of carbonaceous material on graphene and graphite surfaces, which is difficult to remove by conventional techniques. Direct mechanical wiping using a graphite nanoeraser is observed to drastically reduce the amount of contamination. After the mechanical removal of contamination, the graphite surfaces were able to self-retract after shearing, indicating that van der Waals contact bonding is restored. Since contact bonding provides an indication of a level of cleanliness normally only attainable in a high-quality clean-room, we discuss potential applications in preparation of ultraclean surfaces.

cond-mat.mtrl-sci↗

arXiv2010

Preparation of stable excited states in an optical lattice via sudden quantum quench

We study how stable excited many-body states of the Bose-Hubbard model, including both the gas-like state for strongly attractive bosons and bound cluster state for repulsive bosons, can be produced with cold bosonic atoms in an one-dimensional optical lattice. Starting from the initial ground states of strongly interacting bosonic systems, we can achieve stable excited states of the systems with opposite interaction strength by suddenly switching the interaction to the opposite limit. By exactly solving dynamics of the Bose-Hubbard model, we demonstrate that the produced excited state can be a very stable dynamic state. This allows the experimental study of excited state properties of ultracold atoms system in optical lattices.

cond-mat.quant-gas↗

arXiv2010

Spectroscopy of nickel monosulfide in 450 - 560 nm by laser-induced fluorescence and dispersed fluorescence techniques

Laser-induced fluorescence excitation spectrum of NiS in the wavelength range of 450 - 560 nm has been recorded and analyzed. Thirty-five vibronic transition bands have been observed, 29 of which are reported for the first time. Rotational analyses indicated that all the observed bands can be attributable to the [Omega = 0] - X^3 Sigma^- transitions of ^58 NiS (and ^60 NiS). Twenty-five bands have been suggested to be grouped into four vibrational progressions. Furthermore, through dispersed fluorescence measurements we directly obtained the energies for the ground-state vibrational levels up to v" = 6 as well as the vibrational frequency and the anharmonicity constant for the ground state of ^58 NiS.

physics.chem-ph↗

arXiv2010

The B-X and C-X band systems of CuCl revisited: A laser-induced fluorescence study in 465-490 nm

We have reinvestigated the B-X and C-X band systems of CuCl by recording the laser-induced fluorescence excitation spectra in 20400-21800 cm^{-1}. The rotational analyses in Hund's case (a) revealed unambiguously a singlet-to-singlet transition nature. The measured lifetimes of a few microseconds seem too long for singlets and too short for triplets, which we think is actually in favor of a picture of singlet ({1}^Pi and {1}^Sigma^{+})-triplet ({3}^Pi_{0,1,2}) mixed states in the B and C band systems of CuCl. The two excited states we observed in our spectra may be the singlets that have been strongly "contaminated" by their triplet neighbors.

physics.chem-ph↗

arXiv2009

High-order fidelity and quantum phase transition for the Heisenberg chain with next-nearest-neighbor interaction

In this article, we study the high order term of the fidelity of the Heisenberg chain with next-nearest-neighbor interaction and analyze its connection with quantum phase transition of Beresinskii-Kosterlitz-Thouless type happened in the system. We calculate the fidelity susceptibility of the system and find that although the phase transition point can't be well characterized by the fidelity susceptibility, it can be effectively picked out by the higher order of the ground-state fidelity for finite-size systems.

quant-ph↗

arXiv2008

Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD II is envisaged as a three-spacecraft mission which would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.

astro-ph↗

arXiv2008

An almost sure limit theorem for super-Brownian motion

We establish an almost sure scaling limit theorem for super-Brownian motion on $\mathbb{R}^d$ associated with the semi-linear equation $u_t = {1/2}Δu +βu-αu^2$, where $α$ and $β$ are positive constants. In this case, the spectral theoretical assumptions that required in Chen et al (2008) are not satisfied. An example is given to show that the main results also hold for some sub-domains in $\mathbb{R}^d$.

math.PR↗

arXiv2008

Scaling of critical connectivity of mobile ad hoc communication networks

In this paper, critical global connectivity of mobile ad hoc communication networks (MAHCN) is investigated. We model the two-dimensional plane on which nodes move randomly with a triangular lattice. Demanding the best communication of the network, we account the global connectivity $η$ as a function of occupancy $σ$ of sites in the lattice by mobile nodes. Critical phenomena of the connectivity for different transmission ranges $r$ are revealed by numerical simulations, and these results fit well to the analysis based on the assumption of homogeneous mixing . Scaling behavior of the connectivity is found as $η\sim f(R^βσ)$, where $R=(r-r_{0})/r_{0}$, $r_{0}$ is the length unit of the triangular lattice and $β$ is the scaling index in the universal function $f(x)$. The model serves as a sort of site percolation on dynamic complex networks relative to geometric distance. Moreover, near each critical $σ_c(r)$ corresponding to certain transmission range $r$, there exists a cut-off degree $k_c$ below which the clustering coefficient of such self-organized networks keeps a constant while the averaged nearest neighbor degree exhibits a unique linear variation with the degree k, which may be useful to the designation of real MAHCN.

cs.NI↗

arXiv2008

Intrinsic relation between ground-state fidelity and the characterization of a quantum phase transition

The notion of fidelity in quantum information science has been recently applied to analyze quantum phase transitions from the viewpoint of the ground state (GS) overlap for various many-body systems. In this work, we unveil the intrinsic relation between the GS fidelity and the derivatives of GS energy and find that they play equivalent role in identifying the quantum phase transition. The general connection between the two approaches enables us to understand the different singularity and scaling behaviors of fidelity exhibited in various systems on general grounds. Our general conclusions are illustrated via several quantum spin models which exhibit different kinds of QPTs.

cond-mat.other↗

arXiv2008

Quantum dynamics of repulsively bound atom pairs in the Bose-Hubbard model

We investigate the quantum dynamics of repulsively bound atom pairs in an optical lattice described by the periodic Bose-Hubbard model both analytically and numerically. In the strongly repulsive limit, we analytically study the dynamical problem by the perturbation method with the hopping terms treated as a perturbation. For a finite-size system, we numerically solve the dynamic problem in the whole regime of interaction by the exact diagonalization method. Our results show that the initially prepared atom pairs are dynamically stable and the dissociation of atom pairs is greatly suppressed when the strength of the on-site interaction is much greater than the tunneling amplitude, i.e., the strongly repulsive interaction induces a self-localization phenomenon of the atom pairs.

cond-mat.other↗

arXiv2008

Spline-backfitted kernel smoothing of nonlinear additive autoregression model

Application of nonparametric and semiparametric regression techniques to high-dimensional time series data has been hampered due to the lack of effective tools to address the ``curse of dimensionality.'' Under rather weak conditions, we propose spline-backfitted kernel estimators of the component functions for the nonlinear additive time series data that are both computationally expedient so they are usable for analyzing very high-dimensional time series, and theoretically reliable so inference can be made on the component functions with confidence. Simulation experiments have provided strong evidence that corroborates the asymptotic theory.

math.ST↗

arXiv2007

Fidelity and Quantum phase transition for the Heisenberg chain with the next-nearest-neighbor interaction

In this paper, we investigate the fidelity for the Heisenberg chain with the next-nearest-neighbor interaction (or the $J_1-J_2$ model) and analyze its connections with quantum phase transition. We compute the fidelity between the ground states and find that the phase transition point of the $J_1-J_2$ model can not be well characterized by the ground state fidelity for finite-size systems. Instead, we introduce and calculate the fidelity between the first excited states. Our results show that the quantum transition can be well characterized by the fidelity of the first excited state even for a small-size system.

cond-mat.other↗

arXiv2007

Phase diagram of frustrated mixed-spin ladders in the strong-coupling limit

We study the ground-state properties of frustrated Heisenberg ferrimagnetic ladders with antiferromagnetic exchange interactions and two types of alternating sublattice spins. In the limit of strong rung couplings, we show that the mixed spin-1/2 and spin-1 ladders can be systematically mapped onto a spin-1/2 Heisenberg model with additional next-nearest-neighbor exchanges. The system is either in a ferrimagnetic state or in a critical spin-liquid state depending on the competition between the spin exchanges along the legs and the diagonal exchanges.

cond-mat.str-el↗

arXiv2007

Classical and quantum theory for Superluminal particle

As we all know, when the relative velocity of two inertial reference frames $\sum$ and $\sum^{'}$ is less than the speed of light, the relations of $x_μ$ with $x_μ^{'}$, a particle mass $m$ with its velocity $\upsilon$, and a particle mass with its energy are all given by Einstein's special relativity. In this paper, we will give new relation of $x_μ$ and $x_μ^{'}$ when the relative velocity of $\sum$ and $\sum^{'}$ frame is larger than the speed of light, and also we give the relation of a particle mass $m$ with its velocity $\upsilon$, and a particle mass $m$ with its energy $E$ when the particle velocity $v$ is larger than the speed of light.

quant-ph↗

arXiv2007

Quantum theory of electronic double-slit diffraction

The phenomena of electron, neutron, atomic and molecular diffraction have been studied by many experiments, and these experiments are explained by some theoretical works. In this paper, we study electronic double-slit diffraction with quantum mechanical approach. We can obtain the results: (1) When the slit width $a$ is in the range of $3λ\sim 50λ$ we can obtain the obvious diffraction patterns. (2) when the ratio of $\frac{d+a}{a}=n (n=1, 2, 3,\cdot\cdot\cdot)$, order $2n, 3n, 4n,\cdot\cdot\cdot$ are missing in diffraction pattern. (3)When the ratio of $\frac{d+a}{a}\neq n (n=1, 2, 3,\cdot\cdot\cdot)$, there isn't missing order in diffraction pattern. (4) We also find a new quantum mechanics effect that the slit thickness $c$ has a large affect to the electronic diffraction patterns. We think all the predictions in our work can be tested by the electronic double-slit diffraction experiment.

quant-ph↗