$F$为支撑森林的$K_{v}-F$的最大六圈填充

In this paper,we extend the result of packing the complete graph Kv with 6-cycles (hexagons).Mainly,the maximum packing of Kv F is obtained where the leave is an odd spanning forest.     

Cation distribution in Eu-Sc-Fe garnets

The cation distribution has been studied with ⁵⁷Fe Mössbauer spectroscopy in the garnet system Eu_3?ySc_2+yFe₃O₁₂ with y = 0.0, 0.2 and 0.5. It is shown that the previously proposed cation distribution is not correct. The problem of possible impurities in the investigated system is discussed in detail. Several possible cation distributions are considered compatible with Mössbauer data. Mössbauer results combined with the composition dependence of lattice constants show that the tetrahedral sites are accessible to Sc³⁺ ions. The system studied is a second example of a garnet structure in which Sc³⁺ ions are found at the tetrahedral sites. A small fraction of Sc³⁺ ions for the samples y = 0.2 and 0.5 is also found at the dodecahedral sites.     

Dynamics of three-body half collisions: Ultraviolet and visible photodissociation of s-tetrazine

Ultraviolet (266 nm) and visible (532 nm) photodissociation of collision-free s-tetrazine show asymmetric dynamics with production of one translationally cool and one translationally hot HCN molecule. Furthermore, visible and ultraviolet dynamics are nearly identical, arguing that two-photon excitation is necessary for photodissociation in the visible.     

Phytochemical screening and metabolomic approach based on Fourier transform infrared (FTIR): Identification of α-amylase inhibitor metabolites in Vernonia amygdalina leaves

ContextVernonia amygdalina has been reported as a potential antidiabetic agent. One of the mechanisms in diabetes mellitus treatment is the inhibition of the α-amylase enzyme’s action.ObjectiveThis study is aimed to identify the presence of secondary metabolites in Vernonia amygdalina leaf extract, which has the potential as α-amylase inhibitors through phytochemical screening combined with metabolomic analysis.Materials and methodsMethanol extract from Vernonia amygdalina leaf was partitioned into n-hexane, dichloromethane (DCM), and ethyl acetate. From this process, methanol, hexane, DCM, and ethyl acetate extracts were obtained. These extracts were then being tested for phytochemical screening, α-amylase inhibition, and FTIR. Then FTIR data were used for metabolomic analysis (PCA and PLS).ResultsThe results of the α-amylase inhibition test showed that the ethyl acetate extract had the smallest IC50 average value, which was 3.00 μg/mL. Based on the phytochemical screening test results, the extract showed positive for the presence of compounds such as flavonoids, phenols, tannins, alkaloids, and saponins. From the PCA analysis (Bi-plot), the wavenumbers that were influential in the ethyl acetate extract were 1436 to 1681 and 3341 to 3348 cm^?1. In theory, functional groups such as CH, CC, CO, NH, and OH appeared on the absorption. From the PLS analysis, these wavenumbers affected the activity.ConclusionThe most potential extract as an α-amylase inhibitor was the ethyl acetate extract. Based on phytochemical screening tests and metabolomic analysis, it was proven that this extract contained compounds as hypoglycemic agents.     

Moving window as a variable selection method in potentiometric titration multivariate calibration and its application to the simultaneous determination of ions in Raschig synthesis mixtures

A novel method based on moving window (MW) strategy has been proposed to simultaneously choose the optimal pH region and latent variables (LVs) number for partial least squares (PLS) regression in potentiometric titration multivariate calibration. In this method, the leave‐one‐out cross‐validation with varying LVs number is run on different selected MW and, consequently, that revealing optimal results is selected. The method is applied to the simultaneous determination of H⁺, NH₃OH⁺ and NH in Raschig synthesis mixtures, which is of industrial importance. A comparison in the modeling power of PLS is made between non‐processed data set and data set processed by the MW method. Copyright © 2008 John Wiley & Sons, Ltd.     

重大突发事件对国际外汇市场影响分析:基于英国脱欧公投事件

从外汇市场收益率、收益率波动及联动性三个维度全面考察了英国脱欧公投事件对部分世界主要汇率冲击影响全过程。首先,利用时间序列异常点诊断算法研究了公投期间汇率异常波动全过程,发现所有汇率影响显著,但人民币反应具有时滞特征,说明其国际化水平有待进一步提高。进一步,构建了刻画收益率波动的三阶段变结构GARCH模型,结果发现汇率市场异常波动和重大突发事件发生具有显著同步性特征,同时人民币汇率在公投期间波动最小。接着,通过非线性门限协整检验发现汇市之间关联性和共移性较高,公投事件对汇市联动性造成结构性改变,但市场之间依旧保持紧密均衡关系。最后,通过稳健性检验说明了模型选择及结果的合理性。     

The fluorescence of all-trans diphenyl polyenes

The temperature dependence of the fluorescence and fluorescence excitation spectra of all-trans diphenyl hexathene (DPH) and octatetraene (DPO) in six solvents confirms the S₁(¹A_g*) and S₂(¹B_u*) state assignment, and determines their energy difference ΔE. The S₁ fluorescence rate parameter k_F depends on ΔE, the solvent refractive index n, the S₂ (n = 1) fluorescence rate parameter k_F20 (2.23 × 10⁸ s^?1 for DPH, 2.33 × 10⁸ s^?1 for DPO), and the S₂-S₁ coupling matrix element V (745 cm^?1 for DPH, 500 cm^?1 for DPO). The S₁ fluorescence is induced by ¹B_u*-¹A_g* potential interaction (PI), via a b_u vibrational mode (≈ 900 cm^?1), and not by vibronic coupling. The main S₁ radiationless transition, rate parameter k_R, is thermally-activated internal rotation through an angle θ about the central ethylenic bond(s). The PI distorts the S₁ (θ) potential surface and thus influences k_R.     

Self-consistent optimization of molecular geometries by semi-empirical force field method : Part I. Computational scheme

A force field method based on the semi-empirical force approach is used to predict the completely optimized geometries of both the stationary and the saddle points on the molecular energy hyper-surface. The computational aspects are discussed and the organization of computer programs is briefly described. The convergence properties are examined based on the results obtained from MINDO theory.