Panel‐based stratified cluster sampling and analysis for photovoltaic outdoor measurements

We study a stratified multisite cluster‐sampling panel time series approach in order to analyse and evaluate the quality and reliability of produced items, motivated by the problem to sample and analyse multisite outdoor measurements from photovoltaic systems. The specific stratified sampling in spatial clusters reduces sampling costs and allows for heterogeneity as well as for the analysis of spatial correlations due to defects and damages that tend to occur in clusters. The analysis is based on weighted least squares using data‐dependent weights. We show that this does not affect consistency and asymptotic normality of the least squares estimator under the proposed sampling design under general conditions. The estimation of the relevant variance–covariance matrices is discussed in detail for various models including nested designs and random effects. The strata corresponding to damages or manufacturers are modelled via a quality feature by means of a threshold approach. The analysis of outdoor electroluminescence images shows that spatial correlations and local clusters may arise in such photovoltaic data. Further, relevant statistics such as the mean pixel intensity cannot be assumed to follow a Gaussian law. We investigate the proposed inferential tools in detail by simulations in order to assess the influence of spatial cluster correlations and serial correlations on the test's size and power. ©2016 The Authors. Applied Stochastic Models in Business and Industry published by John Wiley & Sons, Ltd.     

Recent Developments in Carbon-Based Nanocomposites for Fuel Cell Applications: A Review

Carbon-based nanocomposites have developed as the most promising and emerging materials in nanoscience and technology during the last several years. They are microscopic materials that range in size from 1 to 100 nanometers. They may be distinguished from bulk materials by their size, shape, increased surface-to-volume ratio, and unique physical and chemical characteristics. Carbon nanocomposite matrixes are often created by combining more than two distinct solid phase types. The nanocomposites that were constructed exhibit unique properties, such as significantly enhanced toughness, mechanical strength, and thermal/electrochemical conductivity. As a result of these advantages, nanocomposites have been used in a variety of applications, including catalysts, electrochemical sensors, biosensors, and energy storage devices, among others. This study focuses on the usage of several forms of carbon nanomaterials, such as carbon aerogels, carbon nanofibers, graphene, carbon nanotubes, and fullerenes, in the development of hydrogen fuel cells. These fuel cells have been successfully employed in numerous commercial sectors in recent years, notably in the car industry, due to their cost-effectiveness, eco-friendliness, and long-cyclic durability. Further; we discuss the principles, reaction mechanisms, and cyclic stability of the fuel cells and also new strategies and future challenges related to the development of viable fuel cells.     

H2S和H2S+的振动光谱和电子能谱计算

本文基于MOLPRO软件包使用从头算方法计算了星际分子H₂S及其阳离子H₂S⁺的势能面及光电子能谱.首先,在(U)CCSD/cc-pVQZ理论水平下获取了H₂S沿法线坐标展开的势能面,势能面直观描述了不同振动模式耦合对分子能量变化的影响,S-H键的非对称伸缩振动和面内弯曲振动共同作用使得系统势能变化范围明显变大.振动多组态相互作用方法被用来计算非谐振动频率和振动光谱,计算结果显示,倍频和组合频之间出现了强烈的费米共振,使得相应波段处的红外强度显著增强.最后,使用拉曼波函数和收缩不变Krylov子空间方法首次计算了H₂SΧ¹A₁→H₂S⁺ X²B₁的光电子能谱.此项研究有助于进一步理解星际分子的内部结构,并为实验研究及星际观测提供参考.     

NO在稀有金属钇表面的吸附行为

以往的理论在预测六方结构(HCP)金属的表面能时,计算值与实验值存在较大误差.鉴于此,本文首先用一种较为合理的方法精准地预测了稀有金属钇(Y)(0001)面的表面能,计算值(1.141 J/M²)与实验值(1.125 J/M²)吻合的很好.随后,系统研究了NO小分子在Y(0001)面不同位置(空位、桥位和端位)的吸附行为.结果表明:空位(H1)表现出了良好的吸附能力,吸附能超过了5eV,同时N-O键长伸长量超过了24%,此时,NO分子几乎平行地吸附于Y(0001)表面.所有的吸附位置的N-O分子伸长量范围为0.2?-0.42?.这种伸长量明显超过了NO在其它金属表面时的计算结果.     

H2S、HCN、PH3在FeO（100）表面吸附的密度泛函理论研究

基于密度泛函理论研究了H2S、HCN、PH3 在FeO(100)表面的吸附行为,其吸附位点主要考虑四个：Fe-top(铁顶位)、O-top(氧顶位)、Hollow(空位)、Bridge(桥位)。结果表明H2S吸附在O-top吸附位点的吸附能最小,为-1.02ev,即在该位点的吸附体系最稳定。当HCN吸附在FeO(100)表面时,各吸附位点的稳定顺序为Hollow>Fe-top>Bridge>O-top。PH3 的最稳定的吸附位点与H2S的一致,为O-top吸附位点,其吸附能为-1.11ev。当H2S吸附在O-top吸附位点时,H2S与FeO（100）表面的电荷转移量最多,说明该吸附构型最稳定,而HCN吸附在FeO(100)表面,在Hollow吸附位点的电荷转移量最多,也即该吸附位点属于最稳定吸附位点。PH3与FeO（100）表面之间的电荷转移量最多的吸附位点与H2S的相同。当H2S和PH3吸附在O-top吸附位点时,吸附后的态密度曲线整体向低能级移动,峰值降低,其吸附结构变得更加稳定。而HCN吸附在Hollow位点时,吸附后的HCN态密度曲线向能量更低的区域移动,吸附体系变得更稳定。     

钪与氧空位共掺杂锐钛矿相TiO2的形成能与电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理研究了钪(Sc)、氧空位(O_V)单/共掺杂锐钛矿相TiO₂,对晶体结构、形成能以及电子结构进行了对比分析.研究结果表明,Sc-TiO₂在富氧环境下缺陷形成能为负值,富钛环境下缺陷形成能为正值,表明Sc-TiO₂只能在富氧环境下制备;O_V-TiO₂、Sc-O_V-TiO₂在富氧或富钛环境下缺陷形成能均为负值,但富氧环境下形成能更低;O_V-TiO₂的0/1-缺陷电荷转变能级为深能级,而Sc-TiO₂的0/1-缺陷电荷转变能级则属于相对较浅能级;与纯锐钛矿相TiO₂相比,Sc-TiO₂的禁带宽度略有减小,但O_V-TiO₂、Sc-O_V-TiO₂禁带宽度变宽.     

基于密度泛函理论的CO2吸附微观机理比较研究

为探究吸附法捕获CO₂过程中的微观机理和吸附剂材料间的作用关系,基于密度泛函理论方法,综合比较了典型吸附剂包括煤基官能团、Fe、限域离子液体、Na₂CO₃、SrTiO₃与CO₂的吸附过程和差异性.根据不同计算策略,着重分析比较了吸附能、结构优化参数、吸附构型以及原子分布等参数.结果表明,化学吸附中CO₂分子与吸附面呈平行关系时通常吸附能最大;在一种材料的同类型官能团中,吸附能大小与氧原子的数量呈正相关关系;吸附过程中C-O键的伸长活化会生成一种重要的中间产物CO₂^-.提出在探寻CO₂吸附材料时可以在含氧原子较多的官能团、活性金属表面等方面进一步探究.最后对基于密度泛函理论的CO₂的吸附机理的进一步研究方向进行了展望.     

稀土X (X=La、Ce、Pr、Nd)修饰单层h-MoS2的NO气敏性

为提高h-MoS₂对NO的气敏性,采用第一性原理研究了X(X=La、Ce、Pr和Nd)对h-MoS₂的稳定性、吸附特性、功函数和伏安特性的影响.研究结果表明：X(X=La、Ce、Pr和Nd)取代Mo原子后得到的形成能均为负,说明掺杂体系容易形成且稳定存在.同时X掺杂后的h-MoS₂布居数相比于未掺杂前的大,也说明掺杂有利于体系稳定.NO吸附在La、Ce原子顶部位置的吸附能为-1.215 eV、-1.225 eV,吸附距离分别为2.475?、2.854?,具有明显的化学吸附特征.同时Hirshfeld转移电荷分别为0.213e和0.325e,具有明显的受体特征,提高了气敏性.La和Ce掺杂后能明显改变功函数的大小,也说明La和Ce能提高h-MoS₂对NO的气敏性.施加电场后能有效提高Pr掺杂体系的吸附强度,增大Hirshfeld转移电荷,对功函数的改变最大,所以电场对Pr掺杂体系的影响非常明显.通过分析掺杂体系的伏安特性曲线,La、Ce两掺杂体系的电流分别由0增大到5.3μA和4.8μA,而Pr、Nd...     

C_2^+ (X^4 Σ_g^-,1^4 Σ_u^+)离子体系解析势能函数、光谱常数和振动能级研究

采用多参考组态相互作用(MRCI)方法,结合aug-cc-pV6Z(AV6Z)基组,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)的势能曲线,计算过程中考虑了Davidson修正和相对论效应,并将结果外推至完备基组(CBS)的极限.基于得到的单点能量,用最小二乘法方法进行了Murrell-Sorbie函数拟合,得到了势能函数解析式(APEF).基于APEF,计算了C₂⁺(X⁴Σ_g^-,1⁴Σ_u⁺)离子体系的离解能D_e,平衡核间距R_e,光谱常数ω_e,ω_eχ_e,B_e,α_e,结果与实验和其他理论计算值符合...