A splitting positive definite mixed element method for second‐order hyperbolic equations

In this article, we establish a new mixed finite element procedure, in which the mixed element system is symmetric positive definite, to solve the second‐order hyperbolic equations. The convergence of the mixed element methods with continuous‐ and discrete‐time scheme is proved. And the corresponding error estimates are given. Finally some numerical results are presented. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009     

A proof of the Gordon Conjecture

A combinatorial proof of the Gordon Conjecture: The sum of two Heegaard splittings is stabilized if and only if one of the two summands is stabilized.     

基于遗传算法的柔性作业车间柔性分批调度问题研究

针对柔性作业车间柔性分批调度问题的复杂性,采用遗传算法进行求解,在引入柔性分批方法后,并提出了染色体的两级编码方法,设计了2种交叉和变异操作方法,以防止操作中非法解的产生,提高求解效率.该算法不仅解决批量分批,而且也解决子批排序和选择加工路线的问题.对比整批调度和柔性分批调度的Makespan后,仿真结果表明,柔性分批调度可缩短生产周期,验证了采用新算法的可行性和有效性.     

在不同应力下石墨烯中拉曼谱的G峰劈裂的变化

应用计及五阶近邻的力常数模型,研究了单轴应力下的石墨烯和芳香烃分子三明治型贴层的石墨烯中拉曼谱的G峰劈裂.计算结果表明对称性的降低解除了G峰对应的在Γ点的面内的纵波光学模声子和横波光学模声子能量简并,从而G峰劈裂为G⁺和G^- 两个峰.在单轴应力作用下,C—C键的伸长致使力常数减小,软化了面内的光学模声子,导致两个G峰都红移;芳香烃分子对石墨烯产生的沿分子长短边方向不同的应力作用,使得G峰对应的两支光学模声子的频率一支发生蓝移,而另一支发生红移.这解 关键词： 力常数模型 石墨烯 拉曼G峰劈裂     

Restored thermoluminescence in oxide crystals

In this paper, we present the results of a thermoluminescence study on several oxide crystals, including Y₃Al₅O₁₂ (YAG), Y₃Al₅O₁₂:Nd (YAG:Nd), Lu₂SiO₅:Ce (LSO:Ce), Y₂SiO₅:Ce (YSO:Ce), Gd₂SiO₅:Ce (GSO:Ce), PbWO (PWO), and PbWO:La (PWO:La). A phenomenon involving restoration of thermoluminescence (TL) glow peaks is found to occur in some of the crystals investigated; crystals γ-irradiated at room temperature and subsequently stored for some time in the dark at 77 K exhibit TL glow peaks in the range below room temperature. This phenomenon is caused not by a thermally or optically stimulated process, but rather as a by-product of a tunneling process. The intensity of the restored TL glow peaks measured in LSO:Ce crystals is found to be proportional both to the radiation dose and to the storage-time at low temperature. A phenomenological theoretical model is proposed, in which tunneling recombination occurs between deep electron and hole traps accompanied by the simultaneous ejection of an electron to the conduction band; some of these conduction electrons then repopulate shallow traps. An oxygen vacancy with two trapped electrons is assumed to be the deep electron trap in this model. The role of oxygen vacancies is confirmed by heating in air at 1000 °C. This model is applied specifically to LSO:Ce, and several possible candidates are suggested for shallow traps in that material.     

塞曼效应测光速实验中影响精度的因素分析

通常情况下该实验用以对电子的荷质比进行测量。笔者发现,如果进行逆向构思,把电子的荷质比作为已知量时,可重新进行理论推导从而得到真空中的光速值。基于该理论基础重新设计塞曼效应试验,就可以得到测量光速的一种新方法。本文主要就采用这一方法测光速时,对影响测量精度的主要因素进行了分析。     

Metal Phosphorous Trichalcogenides (MPCh3): From Synthesis to Contemporary Energy Challenges

Owing to their unique physical and chemical properties, layered two‐dimensional (2D) materials have been established as the most significant topic in materials science for the current decade. This includes layers comprising mono‐element (graphene, phosphorene), di‐element (metal dichalcogenides), and even multi‐element. A distinctive class of 2D layered materials is the metal phosphorous trichalcogenides (MPCh₃, Ch=S, Se), first synthesized in the late 1800s. Having an unusual intercalation behavior, MPCh₃ were intensively studied in the 1970s for their magnetic properties and as secondary electrodes in lithium batteries, but fell from scrutiny until very recently, being 2D nanomaterials. Based on their synthesis and most significant properties, the present surge of reports related to water‐splitting catalysis and energy storage are discussed in detail. This Minireview is intended as a baseline for the anticipated new wave of researchers who aim to explore these 2D layered materials for their electrochemical energy applications.     

Photoelectron Spectroscopy and Theoretical Studies of PCSe−, AsCS−, AsCSe−, and NCSe−: Insights into the Electronic Structures of the Whole Family of ECX− Anions (E=N,P, As; X=O,S, Se)

The newly synthesized phosphorus‐ and arsenic‐containing analogues of the thio‐ and seleno‐cyanate anions, PCSe^?, AsCS^?, and AsCSe^?, as well as the known ion NCSe^? were investigated in the gas phase by negative‐ion photoelectron spectroscopy (NIPES), velocity‐map imaging (VMI) spectroscopy, and quantum‐chemical computations. The electron affinities (EA), spin–orbit (SO) splittings, and “symmetric”/“asymmetric” stretching frequencies of the neutral radicals ECX^. (E=N, P, As; X=S, Se), generated by electron detachment from the corresponding anions, were obtained from the spectra. The calculated EAs, SO splittings, and vibrational frequencies are in excellent agreement with the experimental measurements. These newly obtained values, when combined with those previously determined for the lighter analogues, show interesting trends on descending the pnictogen and chalcogen series. These trends are rationalized based on electronegativity arguments, the electron distributions in the HOMOs, and NBO/NRT analyses.     

Design of Multi-Metallic-Based Electrocatalysts for Enhanced Water Oxidation

Electrochemical water splitting by renewable energy resources is an efficient and green approach for hydrogen gas production. However, the anodic oxygen evolution reaction (OER) largely impedes the industrial application due to its sluggish four-electron-transition kinetics. Although various materials have been developed to accelerate the OER rate, still some issues should be addressed to meet the industrial demand: (i) considerable 200–300 mV overpotential as extra onset energy input, (ii) limited survival and performance in acidic electrolyte for the majority of oxide/hydroxide composite materials, (iii) unsatisfying long-term durability and (iv) the need for facile and scalable preparation methods. Here, we emphasize on multi-metallic composites with enhanced OER activity based on both precious and nonprecious elements that outperform the unary and binary composites. The regulation effect from multi-metal incorporation is also summarized systematically: (i) introducing foreign metal atoms to the host material boosts the physical properties such as conductivity, surface area, defect density, morphology, wettability, etc., (ii) metal doping can synergistically regulate the electronic features of the host material, e. g. oxygen vacancy, e_g orbit filling, coordinative number and covalence state, which can optimize the absorption/desorption energy of the M−O intermediate, (iii) chaotic impact from the added atoms twists the catalyst lattice into a more aggressive and higher energy state, which is more feasible to transform to an active intermediate with lower required energy supply. This review aims to provide a practical approach to further improve the OER performance via multi-metallic-based catalysts.     

Hydrated‐Metal‐Halide‐Based Deep‐Eutectic‐Solvent‐Mediated NiFe Layered Double Hydroxide: An Excellent Electrocatalyst for Urea Electrolysis and Water Splitting

The liquid structures of deep eutectic solvents (DESs) based on hydrated metal halides and their application as electrolytes have been widely studied. However, little attention has been paid to the direct use of this type of DES in the preparation of micro‐/nanomaterials. Herein, an FeCl₃ ? 6 H₂O/urea DES was used in the one‐step synthesis of NiFe‐LDH_D with a nanoflower morphology. In alkaline media, this catalyst promoted excellent electrocatalytic activity for the oxidation of urea at potential of 1.32 V (vs. RHE) and for the oxygen‐evolution reaction at a potential of 1.39 V to achieve a current density of 10 mA cm^?2. These results were superior to the results with NiFe‐LDH/NF that was obtained from an aqueous solution of FeCl₃, as well as most of the previously reported transition‐metal catalysts. Furthermore, NiFe‐LDH_D/NF could be readily implemented as both a cathode and an anode for the electrolysis of urea and water splitting. The use of hydrated‐metal‐halide‐based DESs for the preparation of LDH catalysts through a dipping‐redox strategy should both enrich the research of DESs and offer guidance for the rational surface engineering of catalysts for the electrolysis of urea and overall water splitting with high performance.