Laser-induced phase conversion of n-type SnSe2 to p-type SnSe

We report a facile phase conversion method that can locally convert n-type SnSe₂ into p-type SnSe by direct laser irradiation. Raman spectra of SnSe₂ flakes before and after laser irradiation confirm the phase conversion of SnSe₂ to SnSe. By performing the laser irradiation on SnSe₂ flakes at different temperatures, it is found that laser heating effect induces the removal of Se atoms from SnSe₂ and results in the phase conversion of SnSe₂ to SnSe. Lattice-revolved transmission electron microscope images of SnSe₂ flakes before and after laser irradiation further confirm such conversion. By selective laser irradiation on SnSe₂ flakes, a pattern with SnSe₂/SnSe heteostructures is created. This indicates that the laser induced phase conversion technique has relatively high spatial resolution and enables the creation of micron-sized in-plane p-n junction at predefined region.     

Rolling velocity and relative motion of particle detector in local granular flow

The velocity of a particle detector in granular flow can be regarded as the combination of rolling and sliding velocities. The study of the contribution of rolling velocity and sliding velocity provides a new explanation to the relative motion between the detector and the local granular flow. In this study, a spherical detector using embedded inertial navigation technology is placed in the chute granular flow to study the movement of the detector relative to the granular flow. It is shown by particle image velocimetry (PIV) that the velocity of chute granular flow conforms to Silbert's formula. And the velocity of the detector is greater than that of the granular flow around it. By decomposing the velocity into sliding and rolling velocity, it is indicated that the movement of the detector relative to the granular flow is mainly caused by rolling. The rolling detail shown by DEM simulation leads to two potential mechanisms based on the position and drive of the detector.     

WLAN无感知认证关键技术探讨

WLAN无感知认证是一种由终端自动识别的接入认证方式,为用户提供方便快捷的WLAN接入服务,极大地改变传统繁琐的接入方式,有效地提升用户感知.首先介绍WLAN业务现状及认证存在的问题,通过对IEEE 802.1x体系结构及认证方式的分析,探讨基于EAP身份认证协议的无感知认证方式的技术原理、网络结构、认证流程等关键技术,并对3种主流的无感知认证方法进行详细的分析比较,最后对其应用推广进行总结.     

Long-time asymptotics and the radiation condition with time-periodic boundary conditions for linear evolution equations on the half-line and experiment

The asymptotic Dirichlet-to-Neumann (D-N) map is constructed for a class of scalar, constant coefficient, linear, third-order, dispersive equations with asymptotically time/periodic Dirichlet boundary data and zero initial data on the half-line, modeling a wavemaker acting upon an initially quiescent medium. The large time $t$ asymptotics for the special cases of the linear Korteweg-de Vries and linear Benjamin–Bona–Mahony (BBM) equations are obtained. The D-N map is proven to be unique if and only if the radiation condition that selects the unique wave number branch of the dispersion relation for a sinusoidal, time-dependent boundary condition holds: (i) for frequencies in a finite interval, the wave number is real and corresponds to positive group velocity, and (ii) for frequencies outside the interval, the wave number is complex with positive imaginary part. For fixed spatial location $x$, the corresponding asymptotic solution is (i) a traveling wave or (ii) a spatially decaying, time-periodic wave. The linearized BBM asymptotics are found to quantitatively agree with viscous core-annular fluid experiments.     

Surface‐enhanced Raman scattering investigations on silver nanoparticles deposited on alumina and titania nanotubes: influence of the substrate material on surface‐enhanced Raman scattering activity of Ag nanoparticles

Silver nanoparticles deposited on various ‘inert’ porous materials (mainly Al₂O₃ and TiO₂) are often used as substrates for surface‐enhanced Raman scattering (SERS) measurements. In this study, we used the sputter deposition technique to cover tubular arrays of Al₂O₃ and TiO₂ with Ag nanoparticles. Raman spectra of pyridine (as a probe molecule) and of two selected dyes (5‐(4‐dimethylaminobenzylidene)rhodanine and 5‐(4‐(dimethylamino)benzylidene)‐3‐(3‐methoxypropyl)rhodanine) adsorbed on fabricated Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al substrates were measured. We found that the SERS spectra of pyridine adsorbed on Ag nanoparticles deposited on an Al₂O₃‐n/Al substrate are distinctly different from those measured for an Ag/TiO₂‐n/Ti composite. Similar effects were observed for dyes adsorbed on the surface of both composites. The spectral differences between two kinds of composites (Ag/TiO₂‐n/Ti and Ag/Al₂O₃‐n/Al) are discussed in terms of (1) the modified electronic structure of the Ag nanoparticles due to their interaction with different substrate materials and (2) the different atomic topology of the metal particles thus deposited on the surfaces of the substrates. Composite samples were also studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Copyright © 2012 John Wiley & Sons, Ltd.     

声学超构材料

2000年报道的具有局域共振带隙的声学材料是声学超构材料的前身,也是最早实现的声学超构材料．同光学、电磁超构材料一样,近年来声学超构材料也引起了许多学者的研究兴趣．文章介绍了到目前为止声学超构材料的主要研究进展,内容包括含共振单元的声学超构材料的负有效声学参数（包括质量密度、体模量等）的实现,以及不含共振单元的声学超构材料的一些有效声学参数的确定等,最后对声学超构材料的可能应用进行了简单展望．     

Propagation of local excitations through strongly correlated quantum chains

The propagation of an external transverse magnetic signal acting locally on a 1d chain of spins generates a disturbance which runs through the system. This quantum effect can be interpreted as a classical travelling wave which contains a superposition of a large set of frequencies depending on the size of the chain. Its local amplitude fixes the size of the z-component of the spins at any location in the chain. The average and maximum value of the group velocity are determined and compared with the transmission velocity fixed by the Lieb-Robinson upper bound inequality.     

Optimal selling time in stock market over a finite time horizon

In this paper, we examine the best time to sell a stock at a price being as close as possible to its highest price over a finite time horizon [0, T ], where the stock price is modelled by a geometric Brownian motion and the ’closeness’ is measured by the relative error of the stock price to its highest price over [0, T ]. More precisely, we want to optimize the expression: where (V t ) t≥0 is a geometric Brownian motion with constant drift α and constant volatility σ > 0, M t = max Vs is the running maximum of the stock price, and the supremum is taken over all possible stopping times 0 ≤τ≤ T adapted to the natural filtration (F t ) t≥0 of the stock price. The above problem has been considered by Shiryaev, Xu and Zhou (2008) and Du Toit and Peskir (2009). In this paper we provide an independent proof that when α = 1 2 σ 2 , a selling strategy is optimal if and only if it sells the stock either at the terminal time T or at the moment when the stock price hits its maximum price so far. Besides, when α > 1 2 σ 2 , selling the stock at the terminal time T is the unique optimal selling strategy. Our approach to the problem is purely probabilistic and has been inspired by relating the notion of dominant stopping ρτ of a stopping time τ to the optimal stopping strategy arisen in the classical "Secretary Problem".     

Local influence analysis for semiparametric reproductive dispersion nonlinear models

The present paper proposes a semiparametric reproductive dispersion nonlinear model (SRDNM) which is an extension of the nonlinear reproductive dispersion models and the semiparameter regression models. Maximum penalized likelihood estimates (MPLEs) of unknown parameters and nonparametric functions in SRDNM are presented. Assessment of local influence for various perturbation schemes are investigated. Some local influence diagnostics are given. A simulation study and a real example are used to illustrate the proposed methodologies.