Eu^3+激活氟氧硼酸锗酸盐闪烁玻璃的发光性能

采用传统高温熔融法合成了玻璃组成为B2O3-GeO2-15GdF3-(40-x)Gd2O3-xEu2O3(0≤x≤10)的Eu^3+激活氟氧硼酸锗酸盐闪烁玻璃。在硼锗酸盐玻璃基质中,Gd2O3和GdF3稀土试剂的总含量高达55%,从而确保其密度高于6.4 g/cm^3。闪烁玻璃的光学性能通过光学透过光谱、光致发光光谱、X射线激发发射(XEL)光谱和荧光衰减曲线来表征。玻璃中Gd^3+→Eu^3+离子的能量传递通过激发光谱、发射光谱和Gd^3+-Eu^3+离子间距得到证明,同时也确定了在紫外线和X射线激发下Eu^3+激活氟氧硼酸锗酸盐闪烁玻璃的最佳浓度。Judd-Ofelt理论分析了玻璃中Eu―O键的共价性随Eu^3+掺杂浓度增加而显著增强。Eu^3+激活氟氧硼酸锗酸盐闪烁玻璃在80~470 K温度范围内荧光衰减曲线和发射光谱的温度依赖关系最终证实了其具有较好的发光稳定性。     

锡苯和铅苯二聚反应的理论研究

采用密度泛函理论B3LYP方法,研究了锡苯和铅苯的[2+2],[4+2]及[4+4]二聚反应的微观机理和势能剖面,考察了Sn(Pb)原子上的2,4,6-三甲基苯基(Mes)取代基对反应势能剖面的影响.研究结果表明,所有反应均为协同过程,且大多数情况下,2个C—Sn(Pb)键同步形成.[2+2]和[4+2]反应在热力学和动力学上均比相应的[4+4]反应容易进行,而[4+2]反应在动力学上比相应的[2+2]反应有利.Sn(Pb)原子上的Mes取代基在热力学和动力学上均不利于反应的进行.铅苯的动力学稳定性与锡苯相当,但其热力学稳定性高于锡苯.     

Quantum theory as a description of robust experiments: Derivation of the Pauli equation

It is shown that the Pauli equation and the concept of spin naturally emerge from logical inference applied to experiments on a charged particle under the conditions that (i) space is homogeneous (ii) the observed events are logically independent, and (iii) the observed frequency distributions are robust with respect to small changes in the conditions under which the experiment is carried out. The derivation does not take recourse to concepts of quantum theory and is based on the same principles which have already been shown to lead to e.g. the Schrödinger equation and the probability distributions of pairs of particles in the singlet or triplet state. Application to Stern–Gerlach experiments with chargeless, magnetic particles, provides additional support for the thesis that quantum theory follows from logical inference applied to a well-defined class of experiments.     

The coupled-cluster formalism – a mathematical perspective

ABSTRACT

The Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle.     

Phase transition in the one-dimensional pair-hopping model with unusual one-electron hopping

By modifying the conventional one-electron hopping behavior, we study effects of an occupation-dependent hopping on the ground state of the half-filled one-dimensional pair-hopping model. At weak coupling, the use of bosonization and renormalization-group analysis techniques helps to derive the phase diagram. Such unusual hopping is shown to drive a spin-gap transition and to introduce a new region where the triplet superconducting instability dominates for positively small pair-hopping interaction.     

TBOR-shaped electro-optic modulator with dual output based on double-layer graphene

We proposed an electro-optic modulator with two-bus one-ring (TBOR) structure to improve the extinction ratio and reduce insert loss. It has a dual output compared with one-bus one-ring structure. In addition, double-layer graphene makes it possible for the modulation in the visible to mid-infrared wavelength range. It shows that this new electro-optic modulator can present two switching states well with low insertion loss, high absorption and high extinction ratio. At $\lambda =1550\text{ nm}$, when the switching states are based on the chemical potential, ${\mu }_{\mathrm{c}}=0.38\text{ eV}$ and ${\mu }_{\mathrm{c}}=0.4\text{ eV}$, the insertion losses of both output ports are less than 2 dB, the absorption of the output port coupled via a micro-ring reaches 45 dB and the extinction ratio reaches 14 dB. When the refractive index of the dielectric material is 4.2, the applied voltage will be less than 1.2 V, thus can be used in low-voltage CMOS technology.     

Compressibility of random walker trajectories on growing networks

We find that the simple coupling of network growth to the position of a random walker on the network generates a traveling wave in the probability distribution of nodes visited by the walker. We argue that the entropy of this probability distribution is bounded as the network size tends to infinity. This means that the growth of a space coupled to a random walker situated in it constrains its dynamics to a set of typical random walker trajectories, and walker trajectories inside the growing space are compressible.     

Pentapnictogen heterocyclic monoanions: Structure,stability, and aromaticity

Inorganic planar ring-shape molecules with 4n + 2 π electrons are always the focus of experimental synthesis and theoretical research due to their potential aromaticity and stability. In this work, the whole series of five-membered heterocycle monoanions X _nY_5-n⁻ (X, Y = group 15 elements; n = 1-4) were thoroughly investigated by means of density functional theory calculations. They all have large formation energies and HOMO-LUMO gap energies, suggesting the potential thermodynamic and kinetic stability. Their aromaticities are comparable to that of typical aromatic hydrocarbons. Their thermal stabilities were firmly established by the ab initio molecular dynamics simulations. As most of them are predicted for the first time, their various spectra were simulated for experimental characterization. Furthermore, we demonstrate that these five-membered cyclic anions can be employed as η⁵-ligand to construct novel all-inorganic metallocenes, which may serve as the building blocks of low-dimensional nanomaterials.     

Ligands Based on Phosphine-Stabilized Aluminum(I), Boron(I), and Carbon(0)

A systematic quantum chemical study of the bonding in d⁶-transition-metal complexes, containing phosphine-stabilized, main-group-element fragments, (R₃P)₂E, as ligands (E=AlH, BH, CH⁺, C), is reported. By using energy decomposition analysis, it is demonstrated that a strong M−E bond is accompanied by weak P−E bonds, and vice versa. Although the Al−M bond is, for example, found to be very strong, the weak Al−P bond suggests that the corresponding metal complexes will not be stable towards phosphine dissociation. The interaction energies for the boron(I)-based ligand are lower, but still higher than those for two-carbon-based ligands. For neutral ligands, electrostatic interactions are the dominating contributions to metal–ligand bonding, whereas for the cationic ligand a significant destabilization, with weak orbital and even weaker electrostatic metal–ligand interactions, is observed. Finally, for iron(II) complexes, it is demonstrated that different reactivity patterns are expected for the four donor groups: the experimentally observed reversible E−H reductive elimination of the borylene-based ligand (E=BH) exhibits significantly higher barriers for the protonated carbodiphosphorane (CDP) ligand (E=CH) and would proceed through different intermediates and transition states. For aluminum, such reaction pathways are not feasible (E=AlH). Moreover, it is demonstrated that the metal hydrido complexes with CDP ligands might not be stable towards reduction and isomerization to a protonated CDP ligand and a reduced metal center.     

基于计算机视觉技术的茶叶品质随机森林感官评价方法研究

为弥补茶叶品质感官审评存在的缺陷，利用计算机视觉技术对茶叶品质进行快速无损评价研究。以碧螺春绿茶为对象，依据专家感官审评结果，将茶样分成4个等级；采用中值滤波及拉普拉斯算子对茶样图像进行预处理，并提取预处理后的茶样图像的颜色特征和纹理特征以表征茶叶图像的外形特征，利用随机森林算法对茶叶外形特征属性进行重要性排序；筛选出重要性较大的特征及随机森林算法中最优的决策树棵数建立感官评价模型，并与建立的支持向量机(SVM)模型性能相比较。结果表明：色调均值、色调标准差、绿体均值、平均灰度级、饱和度均值、红体均值、饱和度标准差、亮度均值、一致性等9个特征属性的重要性较大，且与感官审评特征描述结果相一致；当采用优选出的9个重要性较大的特征及决策数棵数为500时，建立的模型性能最优，模型总体判别率为95.75%，Kappa系数为0.933，OOB误差为5%，较SVM模型分别提高了3.5%，0.066，优选的9个重要性较大的图像特征与感官审评特征描述相一致。研究表明：利用随机森林方法筛选出对茶叶外形特征属性贡献最大的少数几个特征建立模型，模型性能就能达到很好的识别效果，模型得到简化，同时模型精度和稳定性都高于其他方法。