三维荧光光谱的特征区域选择方法

将数学中的二元凸函数判定和数据挖掘中的聚类分析方法结合,提出了针对三维荧光的光谱区域选择方法,并利用此种方法从光谱图中提取出含有丰富光谱信息的凸集区域。对水体中总有机碳的检测和白酒中黄曲霉素的检测进行了实验研究,实验结果表明,采用本文提出的三维荧光光谱区域选择方法提高了模型的精度,与利用全光谱所建立的回归模型相比,模型精度分别提高了6.17%和4.97%。     

Global asymptotical stability of a unique almost periodic solution for enterprise clusters based on ecology theory with time-varying delays and feedback controls

This paper is concerned with some dynamic behavior of enterprises cluster constituted by n satellite enterprises and a dominant enterprise. We present a model involving time-varying delays and feedback controls based on ecology theory, which effectively describe the competition and cooperation of enterprises cluster in real economic environments. Applying the comparison theorem of differential equations and constructing a suitable Lyapunov functional, sufficient conditions which guarantee the existence of a unique globally asymptotically stable nonnegative almost periodic solution of the system are obtained. Finally, we present an example to explain the economical significance of mathematical results.     

多元统计分析方法的理论研究及应用分析

多元统计分析在多指标实际问题的研究中起着重要的作用.以往文献中,一般采用某一种多元统计方法对一个多指标实际问题进行研究,但其结果存在一定的偏差性.采用四种典型的多元统计方法:主成分分析法、因子分析法、分层聚类和K-均值聚类方法对同一个多指标银行问题进行研究,并对四种方法的不同结果进行比较综合分析,这样可以避免单一方法的偏差性,以便得到的结果更合理、更具有说服力.     

Unravelling Structural Mysteries of Simple Organozinc Alkoxides

Simple RZnOR’ alkoxides are among the first known organozinc compounds, and widespread interest in their multifaced chemistry has been driven by their fundamental significance and potential applications including various catalytic reactions. Nevertheless, their chemistry in solution and in the solid state remains both relatively poorly understood and a subject of constant debate. Herein, the synthesis and structural characterization of long-sought structural forms, a roof-like trimer [(tBuZn)₃(μ-OC(H)Ph₂)₂(μ₃-OC(H)Ph₂)] and a ladder-type tetramer [(PhZn)₄(μ-OC(H)Ph₂)₂(μ₃-OC(H)Ph₂)₂], incorporating diphenylmethanolate as a model alkoxide ligand, are reported. Both novel aggregates are robust in the solid state and resistant towards mechanical force. By using ¹H NMR and diffusion-order spectroscopy, it is demonstrated that new RZnOR’ alkoxides are kinetically labile in solution and readily undergo ligand scrambling, such as in the case of Schlenk equilibrium. The elucidated key structural issues, which have remained undiscovered for decades, significantly advance the chemistry of RZnOR’ alkoxides and should support the rational design of zinc alkoxide-based applications.     

DRDF analysis of wide-angle x-ray scattering of natural rubber

A differential radial distribution function (DRDF) of molten natural rubber (NR) was derived from its wide-angle x-ray scattering (WAXS) data. Three peaks with Bragg spacings 4.85, 2.31, and 1.23 Å corresponding, respectively, to interchain, C₁-C₃ and C₁ -C₂ distances are present in the corrected WAXS curve. The derived DRDF, which is shown to be greatly improved than the ones published so far, contains six peaks located at 1.51, 2.48, 3.98, 5.68, 10.65, and 15.25 Å. Maximum contributions of intramolecular atomic distances to the radial distribution peaks were estimated and compared with the experimental results. The comparison shows that the first three peaks are intramolecular in origin and the remaining peaks are predominantly due to intermolecular regularities. A periodicity of an approximately constant interval of 5.26 Å is found between the intermolecular peaks and is attributable to the organizations of more or less parallel chain segments in the material. This finding provided additional evidence for the presence of local lateral ordering to the extent of about 30 Å in molten-state natural rubber.     

W4Br10 Cluster Intermediates in the Solid State Nucleation of W6Br12

The new adduct W₄Br₁₀ · 2SbBr₃ and the new binary compound W₄Br₁₀ were obtained as products in a reaction cascade in which WBr₆ was reacted with elemental antimony at successively increased temperatures. The crystal structures of both compounds were refined from X‐ray powder diffraction data and their electronic structures were analyzed by MO calculations. The cluster compounds W₄Br₁₀ · 2SbBr₃ and W₄Br₁₀ appear as intermediates in the solid state nucleation of W₆Br₁₂. The overall reaction cascade involves tungsten clusters having tetrahedral (W₄), square pyramidal (W₅) and finally octahedral (W₆) cluster cores.     

Is it True That the Normal Valence‐Length Correlation Is Irrelevant for Metal–Metal Bonds?

The most intriguing feature of metal–metal bonds in inorganic compounds is an apparent lack of correlation between the bond order and the bond length. In this study, we combine a variety of literature data obtained by quantum chemistry and our results based on the empirical bond valence model (BVM), to confirm for the first time the existence of a normal exponential correlation between the effective bond order (EBO) and the length of the metal–metal bonds. The difference between the EBO and the formal bond order is attributed to steric conflict between the (TM)_n cluster (TM=transition metal) and its environment. This conflict, affected mainly by structural type, should cause high lattice strains, but electron redistribution around TM atoms, evident from the BVM calculations, results in a full or partial strain relaxation.     

The Key Role of U28 in the Aqueous Self‐Assembly of Uranyl Peroxide Nanocages

For 11 years now, the structural diversity and aesthetic beauty of uranyl–peroxide capsules have fascinated researchers from the diverse fields of mineralogy, polyoxometalate chemistry, and nuclear fuel technologies. There is still much to be learned about the mechanisms of the self‐assembly process, and the role of solution parameters including pH, alkali template, temperature, time, and others. Here we have exploited the high solubility of the UO₂²⁺/H₂O₂/LiOH aqueous system to address the effect of the hydroxide concentration. Important techniques of this study are single‐crystal X‐ray diffraction, small‐angle X‐ray scattering, and Raman spectroscopy. Three key phases dominate the solution speciation as a function of time and the LiOH/UO₂²⁺ ratio: the uranyl–triperoxide monomer [UO₂(O₂)₃]^4?and the two capsules [(UO₂)(O₂)(OH)]₂₄^24?(U₂₄) and [(UO₂)(O₂)_1.5]₂₈^28?(U₂₈). When the LiOH/U ratio is around three, U₂₈ forms rapidly and this cluster can be isolated in high yield and purity. This result was most surprising and challenges the hypothesis that alkali templating is the most important determinant in the cluster geometry. Moreover, analogous experiments with KOH, NH₄OH, and TEAOH (TEA=tetraethylammonium) also rapidly yield U₂₈, which suggests that U₂₈ is the kinetically favored species. Complete mapping of the pH–time phase space reveals only a narrow window of the U₂₈ dominance, which is why it was previously overlooked as an important kinetic species in this chemical system, as well as others with different counterions.