Developing a time-domain finite-element method for modeling of electromagnetic cylindrical cloaks

In this paper we propose a time-domain finite element method for modeling of electromagnetic cloaks. The permittivity and permeability of the cloak model are described by the Drude dispersion model. The model to be solved is quite challenging in that we have to solve a coupled problem with different partial differential equations given in different regions. Our method is based on a mixed finite element method using edge elements with different types of meshes in different regions. Numerical results demonstrate that our algorithm is quite effective for simulating cloaks in time-domain. To our knowledge, this is the first cloak simulation carried out by the time-domain finite element method.     

Synthesis and characterization of the efficient visible-light-induced photocatalyst AgBr and its photodegradation activity

AgBr photocatalysts were prepared with the 1-hexadecyl-3-methylimidazolium bromide ([C₁₆mim]Br) reactable ionic liquid at different temperatures by one-step hydrothermal method, in which the ionic liquid acted as a precursor and a template to control the size of AgBr crystal. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), the Brunauer–Emmett–Teller (BET) surface area and diffuse reflectance spectroscopy (DRS). Methyl orange (MO) dye was chosen as a model pollutant to investigate the photocatalytic activity and the stability of the samples under visible light irradiation. The results indicated that the AgBr photocatalysts showed high efficiency in the degradation of MO under visible light irradiation. The kinetic property of the reaction followed the first-order reaction model. During the photocatalytic degradation reaction, AgBr was transformed to the Ag⁰/AgBr composite. However, the photocatalytic efficiency was still high and the photocatalytic activity was stable. The possible photocatalytic mechanism of the photocatalysts was also eventually proposed.     

Changes in surface morphology and work function caused by corrosion in aluminum alloys

Corrosion behavior of a material is complicated and can affect strongly its surface physical and chemical properties. In this study, the effect of corrosion on surface morphology and electron work function (EWF) of various Al alloys was comparatively investigated using a scanning electron microscopy and a scanning Kelvin probe. The experimental results showed that the change in EWF with corrosion time was not linear, but firstly increased and then decreased. The theoretical treatments demonstrated that such a change in EWF did not only depend on the surface roughness, but also correlate with oxide layers formed at the surfaces of Al alloys. The present results can also be used to reasonably explain the correlation between surface roughness and EWF reported previously.     

Measurements of dynamics of nondegenerate optical nonlinearity in ZnS with pulses from optical parameter generation

We expand the degenerate PO pump-probe technique to nondegenerate field and use it to investigate optical nonlinear dynamics in ZnS single crystal. Excited by 532-nm laser pulses with 21-ps duration, the temporal response of nondegenerate nonlinear absorption and nondegenerate nonlinear refraction are probed by laser pulses from optical parameter generation (OPG) at 600 and 680 nm with pulse width of 10 ps. Based on the theory of free-carrier optical nonlinearity, we study the pure free-carrier refraction in ZnS. By numerically fitting based on the nondegenerate pump-probe theory, the nondegenerate two-photon absorption coefficient, the free-carrier lifetime, the free-carrier absorptive cross section and refractive coefficient at both probe wavelengths are determined respectively. The dispersion of the free-carrier refractive coefficients is discussed.     

License plate location based on trichromatic imaging and color-discrete characteristic

License plate location (LPL) is the key part of automatic license plate recognition (LPR) system that plays an important role in many applications and a number of LPL methods based on color information have been proposed. However, some problems, such as country specific, similar color interference, lighting variation sensitive, time consuming, processing only one kind of LP with same color combination a time and omitting the case of more than one combinations in a LP, should be solved further. In this study, a color-based LPL method that consists of three modules: color edge extraction, denoising and searching, is proposed. Color edge extraction, the kernel of the proposed, is designed by color-discrete characteristics of license plates in the trichromatic wavebands. In the experiment, 1384 images taken from natural scenes in China and other 104 countries or regions are employed. Of which, 74 have been failed to locate the license plates. The success rate and average execution time are 94.7% and 57 ms, respectively.     

Self-mixing effect in Yb3+ doped DBR fiber laser with different linewidth enhancement factor

We present a self-mixing interference model approach to stimulate the self-mixing interference in YDBR fiber laser with optical self-mixing interference operating in the weak feedback regime. The self-mixing interference model includes Yb³⁺ doped fibers pumped at 920 nm, with distributed Bragg reflector mirrors at both fiber ends and external reflector. Using the quasi-analytical YDBR fiber laser model and self-mixing three-mirror cavity model, the output power expression is deduced and the Peak-to-Peak values and asymmetry values of self-mixing waveform at different linewidth enhancement factor have been studied in detail.     

First-principles studies on the structural and electronic properties of Li-ion battery cathode material CuF2

The 3d transition metal binary compounds have been extensively investigated for a large multi-electron redox capacity through reversible electrochemical reactions. Here, the structural, electronic and magnetic properties of CuF₂ are studied by the first-principles calculations within both the generalized gradient approximation (GGA) and GGA+U frameworks. Our results show that the antiferromagnetic (AFM) configuration of CuF₂ is more stable than the ferromagnetic (FM) one, which is consistent with experiments. The analysis of the electronic density of states (DOS) shows that CuF₂ is a classic Mott–Hubbard insulator with a large d–d type band gap, which is similar to the case of FeF₃. Moreover, small spin polarizations were found on the sites of fluorin ions, which accords with a fluorin-mediated superexchange mechanism for the Cu–Cu magnetic interaction.     

Dynamics of quantum discord in the purification process

We investigate the dynamics of quantum discord during the purification process. In the case of Werner states, it is shown that quantum discord is increased after a round of purification protocol. Furthermore, quantum mutual information and classical correlation is also increased during this process. We also give an analytic expression for a class of higher dimensional states which have additive quantum discord.     

The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering

This paper seeks to determine the optimal settings for the deposition parameters, for TiO₂ thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO₂ target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (°C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO₂. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (1 1 0) and (2 0 0) peaks of the rutile structure and the (2 0 0) peak of the anatase structure were observed, at 2θ ∼ 27.4°, 39.2° and 48°, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO₂ film, because of the increased strength of the interface of micro-blasted tools.