基于连续投影算法的光谱主成分组合优化方法研究

应用连续投影算法(successive projections algorithm, SPA)选择由主成分分析(principal component analysis,PCA)得到主成分的最佳组合。首先对奶粉的短波近红外光谱进行PCA分析, 然后通过SPA得到的脂肪和蛋白质含量预测最佳主成分组合分别为主成分1,2,4,5,6和7以及主成分1,2,3,4,5和8。通过最小二乘支持向量机(Least-squares support vector machine, LS-SVM)对奶粉中脂肪和蛋白质含量进行预测, SPA选择得到的主成分组合均优于分别采用前4个到前8个主成分。 基于SPA得到的主成分组合得到脂肪含量预测结果的确定系数(R2p),预测误差均方根(root mean square error for prediction, RMSEP)和剩余预测偏差(residual predictive deviation, RPD)分别为0.989 0,0.170 3和9.534 3。而蛋白质含量预测结果的R2p,RMSEP和RPD分别为0.987 6,0.134 8和8.927 4。说明SPA能够用于快速有效选取最佳的主成分数, 寻优过程简单快速,并且不用对大量参数进行调试。     

Measurability and countable separation

We introduce several types of countable separation and we give necessary and sufficient conditions, in terms of measurability of some sets constructed by means of multifunctions, in order that a topological space satisfies such a property. We give a characterization of measurability of multifunctions in terms of their graphs.     

Physically based molecular device model in a transient circuit simulator

Two efficient, physically based models for the real-time simulation of molecular device characteristics of single molecules are developed. These models assume that through-molecule tunnelling creates a steady-state Lorentzian distribution of excess electron density on the molecule and provides for smooth transitions for the electronic degrees of freedom between the tunnelling, molecular-excitation, and charge-hopping transport regimes. They are implemented in the fREEDA™ transient circuit simulator to allow for the full integration of nanoscopic molecular devices in standard packages that simulate entire devices including CMOS circuitry. Methods are presented to estimate the parameters used in the models via either direct experimental measurement or density-functional calculations. The models require 6–8 orders of magnitude less computer time than do full a priori simulations of the properties of molecular components. Consequently, molecular components can be efficiently implemented in circuit simulators. The molecular-component models are tested by comparison with experimental results reported for 1,4-benzenedithiol.     

Nonisothermal Kinetics of Sub‐Solidus Phase Transitions in C10Zn,C16Zn and Their Binary System

Nonisothermal kinetics of the solid‐solid phase transition in (n‐C₁₀H₂₁NH₃)₂ZnCl₄(C₁₀Zn), (n‐C₁₆H₃₃NH₃)₂ZnCl₄(C₁₆Zn) and their binary system were determined by Kissinger and Ozawa methods from DSC measurements. The activation energy E_a of the binary system shows a waving dependence on W_C10Zn%, which is caused by not only an intermediate (C₁₀H₂₁NH₃)(n‐C₁₆H₃₃NH₃)ZnCl₄ but also three solid solution ranges (α, β, γ) in the phase diagram of C₁₀Zn‐C₁₆Zn. The variations of the layer d‐spacing are also convenient for the above result.     

X-ray magnetic circular dichroism of Pseudomonas aeruginosa nickel(II) azurin

We show that X-ray magnetic circular dichroism (XMCD) can be employed to probe the oxidation states and other electronic structural features of nickel active sites in proteins. As a calibration standard, we have measured XMCD and X-ray absorption (XAS) spectra for the nickel(II) derivative of Pseudomonas aeruginosa azurin (NiAz). Our analysis of these spectra confirms that the electronic ground state of NiAz is high-spin (S = 1); we also find that the L(3)-centroid energy is 853.1(1) eV, the branching ratio is 0.722(4), and the magnetic moment is 1.9(4) mu(B). Density functional theory (DFT) calculations on model NiAz structures establish that orbitals 3d(x2-y2) and 3d(z2) are the two valence holes in the high-spin Ni(II) ground state, and in accord with the experimentally determined orbital magnetic moment, the DFT results also demonstrate that both holes are highly delocalized, with 3d(x2-y2) having much greater ligand character.     

O2 interaction and reactivity on a model hydroxylated rutile(110) surface

Recently several theoretical studies have examined oxygen adsorption on the clean, reduced TiO2(110) surface. However the photocatalytic behavior of TiO2 and the scavenging ability of oxygen are known to be influenced by the presence of surface hydroxyls. In this paper the chemistry of O2 on the hydroxylated TiO2 surface is investigated by means of first-principles total energy calculations and molecular dynamics (MD) simulations. The MD trajectories show a direct, spontaneous reaction between O2 and the surface hydroxyls, thus supporting the experimental hypothesis that the reaction does not necessarily pass through a chemisorbed O2 state. Following this reaction, the most stable chemisorbed intermediates are found to be peroxide species HO2 and H2O2. Although these intermediates are very stable on the short time scale of MD simulations, the energetics suggests that their further transformation is connected to a new 300 K feature observed in the experimental water temperature programmed desorption (TPD) spectrum. The participation of two less stable intermediate states, involving terminal hydroxyls and/or chemisorbed water plus oxygen adatoms, to the desorption process, is not supported by the total energy calculations. Analysis of the projected density of states, however, suggests the possibility that these intermediates have a role in completing the surface oxidation immediately before desorption.     

N‐Doped Carbon Aerogel Derived from a Metal–Organic Framework Foam as an Efficient Electrocatalyst for Oxygen Reduction

Metal–organic frameworks (MOFs) are promising alternative precursors for the fabrication of heteroatom‐doped carbon materials for energy storage and conversion. However, the direct pyrolysis of bulk MOFs usually gives microporous carbonaceous materials, which significantly hinder the mass transportation and the accessibility of active sites. Herein, N‐doped carbon aerogels with hierarchical micro‐, meso‐, and macropores were fabricated through one‐step pyrolysis of zeolitic imidazolate framework‐8/carboxymethylcellulose composite gel. Owing to the hierarchical porosity, high specific surface area, favorable conductivity, excellent thermal and chemical stability, the as‐prepared N‐doped carbon aerogel exhibits excellent oxygen reduction reaction (ORR) activity, long‐term durability, and good methanol tolerance in alkaline medium. This work thus provides a new way to fabricate new types of MOF‐derived carbon aerogels for various applications.