A Theoretical Perspective to Study the Optical Properties of Tetrafluoroborates

In this study, a series of tetrafluoroborates with non-π-conjugated [BF₄] tetrahedra are investigated systematically by first-principles calculations. Theoretical studies demonstrate that tetrafluoroborates with alkali and/or alkaline-earth metals are more favorable for deep-ultraviolet transmission and are comparable to the classical deep-ultraviolet (deep-UV) material, MgF₂. Furthermore, bandgap decrease with the increasing of ionic radii in alkali and/or alkaline-earth metals. Introducing highly polarizable cations with d₁₀-configuration or cations with lone pair electrons into the structure will decrease the bandgaps. The birefringence and second harmonic generation effects are not large enough in tetrafluoroborates because polarizability anisotropy and hyperpolarizability in non-π-conjugated [BF₄] tetrahedra are much smaller than those in π-conjugated groups. However, the second harmonic generation effect for [BF₄] tetrahedra has a higher contribution in comparison with that due to birefringence. To effectively synthesize the borate fluorides or fluorooxoborates in the deep-UV region, raw materials with B−F bonds are preferred.     

Mechanical and electrochemical properties of platinum coating by double glow plasma on titanium alloy substrate

In this paper, a platinum coating was deposited on titanium alloy substrate by a double glow plasma. Phase and microstructure of platinum coating were examined by X-ray diffraction and scanning electron microscopy, respectively. The microhardness of the coating was estimated by nanoindentation instrument. The adhesive force between the coating and the substrate was performed with scratch tester. The electrochemical behavior of the platinum coating in 3.5 wt % sodium chloride solution was investigated by potentiodynamic polarization. The results indicated that an adherent platinum coating could be successfully obtained on titanium alloy substrates. Compared with the titanium alloy substrate, the platinum coating had a relative low corrosion current density and high corrosion potential. It indicated that the platinum coating had a better corrosion resistance than the titanium alloy substrate.     

硝酰氯的大气化学

硝酰氯(nitryl chloride,ClNO₂)是大气中一种重要的气态污染物,对大气氧化性、一次污染物的降解和二次污染物的生成具有重要影响,并在全球氮循环和氯循环中扮演着不可忽视的角色。本文归纳了ClNO₂的基本物理化学性质及其在大气中的生成和去除机制,并介绍了实验室研究和外场观测中ClNO₂的主要测量方法。在此基础上,本文总结了过去十几年报道的ClNO₂在实际大气中的时空分布特征,通过分析实验室模拟和外场观测的研究结果系统讨论了ClNO₂非均相生成的机制、产率及其影响因素,探讨了ClNO₂对氯自由基、大气氧化性以及臭氧和硝酸盐形成的影响。我们指出,ClNO₂既耦合了气相化学和非均相化学,又耦合了夜间大气化学和日间光化学,在我国大气复合污染中可能起着非常重要的作用。最后,本文提出了ClNO₂大气化学研究中尚待解决的关键科学问题,并简要讨论了该领域的未来发展方向。     

Multiplesite structure and photoluminescence properties of Eu3+ doped MgO nanocrystals

MgO:Eu³⁺ nanocrystals with average diameter around 15 nm were prepared via a facile combustion method under a weak reductive atmosphere at temperature as low as 300°C. The photoluminescence spectra showed that the MgO:Eu³⁺ nanocrystals emit white light, the hypersensitive transition (⁵ D ₀→⁷ F _j of Eu³⁺) emission was prominent in the emission spectra resulting from the noinversion symmetry local site at which Eu³⁺ ions were located. Two kinds of luminescence sites of Eu³⁺ are identified by means of the fluorescence decay and site-selective spectroscopy. The excitation and absorption spectra indicated that the absorption of surface state decreased with the increase of Eu³⁺ concentration, meaning that the surface defect decreased through Eu³⁺ doping for some of them located at the disordered sites near the surface or absorbed at the surface of MgO host. Meanwhile, absorptivity and CIE chromaticity coordinates of all samples were measured; the results were in accordance with the excitation and absorption spectra and photoluminescence spectra, respectively.     

超声管形振子的振动分析

基于Flügge壳体理论,利用严格解法得出了自由边界条件下超声管形振子纵径耦合振动的频率方程,研究了长径比、径厚比及泊松比等参数对振子振动频率的影响,并和薄膜简支边界条件下的振动情况进行了对比;通过与表观弹性法进行比较研究,探讨了表观弹性法的精度;最后用严格解法计算了管形振子的振型曲线,对其纵径转换效率进行了分析.研究...     

Strangeonium-like hybrids on the lattice

The strangeonium-like ss^-g hybrids are investigated from lattice QCD in the quenched approximation.In the Coulomb gauge,spatially extended operators are constructed for 1^--and(0,1,2)^-+states with the color octet ss^-component being separated from the chromomagnetic field strength by the spatial distance r,whose matrix elements between the vacuum and the corresponding states are interpreted as Bethe-Salpeter(BS)wave functions.In each of the(1,2)^-+channels,the masses and the BS wave functions are reliably derived.The 1^-+ground state mass is approximately 2.1-2.2 GeV,and that of 2^-+is approximately 2.3-2.4 GeV,whereas the mass of the first excited state is approximately 1.4 GeV higher.This mass splitting is much larger compared to that expected based on the phenomenological flux-tube model or constituent gluon model for hybrids,which is usually a few hundred MeV.The BS wave functions with respect to r exhibit clear radial nodal structures of a non-relativistic two-body system,which imply that r is a meaningful dynamical variable for these hybrids and motivate a color halo picture of hybrids,in which the color octet ss^-is surrounded by gluonic degrees of freedom.In the 1^--channel,the properties of the lowest two states are consistent with those ofФ(1020)andФ(1680).We did not obtain convincing information with respect toФ(2170).However,we argue that regardless of whetherФ(2170)is a conventional ss^-meson or a ss^-g hybrid in the color halo scenario,the ratio of partial decay widthsΓ(Фη)andΓ(Фη')observed by BESIII can be understood based on the mechanism of hadronic transition of a strangeonium-like meson in addition toη-η'mixing.     

A Quantum Watermarking Protocol Based on Bell Dual Basis

This paper presents a Bell-dual-basis-based quantum watermarking protocol composed of three major algorithms: watermark embedding and extracting and the intercepting test. The first two are completed by using the entanglement swapping property of Bell dual basis and the test is accomplished through IBF protocol to guarantee its bottom security. The watermarking protocol is mainly designed for the protection of digital copyright in the existence of classical information. This design finds that the quality of digital contents is not damaged with its zero-watermark attributes when embedding watermarks.     

Time-Dependent Methane Diffusion Behavior in Coal: Measurement and Modeling

In-depth understanding of how methane diffuses in porous media like coal is critical for enhanced coalbed methane recovery and coal seam methane drainage. However, the classic unipore gas diffusion model can only describe methane diffusion behavior in coal at the early time diffusion stage. Describing the whole methane diffusion behavior in coal has not been reasonably addressed in the coalbed methane field. Considering the large surface-to-volume ratio of coal, the authors proposed a time-dependent gas diffusion model to describe the whole diffusion process. This work first proposed a power–law relationship between diffusion coefficient and time according to previous studies of the time-dependent gas diffusion process in porous media. Then, both the analytical solution and its approximation solution for the time-dependent gas diffusion model were derived. Six methane diffusion tests in crushed coal were conducted to validate the proposed model under different pressures (0.5, 1.5, 2.5 MPa) and temperatures (20 and \(30\,{^{\circ }}\hbox {C}\)). Modeling results show that the time-dependent gas diffusion model is superior to the classic unipore gas diffusion model for describing the whole methane diffusion process in coal. Increasing temperature always accelerates methane diffusion in coal; the higher the temperature the larger the diffusion coefficient.     

A coupled-channel lattice study of the resonance-like structure Zc(3900)

In this exploratory study, near-threshold scattering of D and \begin{document}$\bar{D}^*$\end{document} meson is investigated using lattice QCD with \begin{document}$N_f=2+1+1$\end{document} twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with \begin{document}$I^G(J^{PC})=1^+(1^{+-})$\end{document} where the resonance-like structure \begin{document}$Z_c(3900)$\end{document} was discovered. We first identify the two most relevant channels and the lattice study is performed in the two-channel scattering model. Combined with the two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results for the scattering length parameters suggest that for the particular lattice parameters that we studied, the best fit parameters do not correspond to the peak in the elastic scattering cross-section near the threshold. Furthermore, in the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond the 3\begin{document}$\sigma$\end{document} level.