一种改进的随机检验法用于主成分选择以避免光谱分析校正模型的过拟合或欠拟合

为了避免主成分个数选择不当引起的校正模型过拟合或欠拟合,提出了一种改进的随机检验法,应用该方法对样品复杂程度递增的三组近红外光谱数据进行了实验研究,并与交互验证法进行了比较,分析了模型复杂程度对光谱定量校正模型预测能力的影响,讨论了该方法对复杂样品的适用性问题。结果显示,该方法可避免交互验证法剔除样本的过程,考虑了全部训练样本的信息,可客观地选择主成分,有助于避免过拟合或欠拟合,提高校正模型的预测精度;该方法不同于一般随机检验法的统计检验过程,简化了判据,易实现,选择过程可视化、可交互;在三组实验中,分别选择4,5和8个主成分建模,其外部独立预测集的预测结果最优;该方法适用于小样本复杂样品建模。     

Effective charges in the fp shell

Following the heavy-ion fusion-evaporation reaction 32S+24Mg at 95 MeV beam energy the lifetimes of analogue states in the T(z)=+/-1/2 A=51 mirror nuclei 51Fe and 51Mn have been measured using the Cologne plunger device coupled to the GASP gamma-ray spectrometer. The deduced B(E2;27/2(-)-->23/2(-)) values afford a unique opportunity to probe isoscalar and isovector polarization charges and to derive effective proton and neutron charges, epsilon(p) and epsilon(n), in the fp shell. A comparison between the experimental results and several different large-scale shell-model calculations yields epsilon(p) approximately 1.15e and epsilon(n) approximately 0.80e.     

A study of madelung potential effects in the ESCA spectra of the metal oxides

Madelung potentials, assuming the normal oxidation states of the ions involved, have been calculated within the point-charge approximation for most of the common metal oxides, and an empirical expression has been found for obtaining these potentials to a high degree of accuracy. Using these potentials and core binding-energy shifts of the free ions [1], calculated and experimental ESCA spectra have been compared. Deficiencies of the simple Madelung-potential model are discussed, and trends in the ionicity of the oxides are obtained.     

A new method to test virtual photon spectra

Millisecond isomers in¹⁴⁶Tb,¹⁴⁸Ho and¹⁵⁰Tm, observed in⁶⁰Ni reactions on³⁹Y,⁹⁰Zr, and⁹²Mo targets, are interpreted as (πh_11/2 vh_11/2 ^?1) 10⁺ isomers predicted by the shell model. Their decays are characterized.     

A new method for ESCA studies of liquid-phase samples

A new technique is described for obtaining ESCA spectra from liquid-phase samples. It combines temperature regulation of the liquid samples, which are continuously created as thin films on a metal backing, with the use of monochromatized A1 Kα radiation for excitation. The technique is simple to implement and can be used routinely over essentially unlimited periods of recording time in the spectrometer. The results show substantially increased quality with respect to earlier measurements in terms of signal-to-background ratio and resolution. The technique also implies a vast increase in the number of solvents usable for future liquid-phase ESCA work.     

K‐edge XANES analysis of sulfur compounds: an investigation of the relative intensities using internal calibration

Sulfur K‐edge XANES (X‐ray absorption near‐edge structure) spectroscopy is an excellent tool for determining the speciation of sulfur compounds in complex matrices. This paper presents a method to quantitatively determine the kinds of sulfur species in natural samples using internally calibrated reference spectra of model compounds. Owing to significant self‐absorption of formed fluorescence radiation in the sample itself the fluorescence signal displays a non‐linear correlation with the sulfur content over a wide concentration range. Self‐absorption is also a problem at low total absorption of the sample when the sulfur compounds are present as particles. The post‐edge intensity patterns of the sulfur K‐edge XANES spectra vary with the type of sulfur compound, with reducing sulfur compounds often having a higher post‐edge intensity than the oxidized forms. In dilute solutions (less than 0.3–0.5%) it is possible to use sulfur K‐edge XANES reference data for quantitative analysis of the contribution from different species. The results show that it is essential to use an internal calibration system when performing quantitative XANES analysis. Preparation of unknown samples must take both the total absorption and possible presence of self‐absorbing particles into consideration.     

一种显示器颜色特性的反向查找新方法

根据实验的数据建立了CRT的设备颜色空间(RGB空间)与标准颜色空间(CIELAB空间)之间的颜色特性转换模型。通过分析大量的实验测量数据,以改进的三维查找表形式建立了RGB和L*a*b*之间的正逆转换关系。其中正向查找表的建立是按照三维线性的插值方法,逆向查找表的建立则利用一种插值和迭代相结合的新方法,使L*a*b*查找到较为准确的RGB值。通过用标准图像的的随机误差检验,其转换的平均色差ΔE为0.9286色差单位。     

Effective charges of the valence shells on atoms of A15 chemical compounds

X-ray diffraction data are used to calculate the charges of the valence shells of Si and V in V₃Si. The subsequent integration of the deformation density $\text{(?}{}_{\mathrm{def}}\text{(}\text{¬}\text{→}\text{) = ?}{}_{\exp }\text{(}\text{¬}\text{→}\text{) ? ?}{}_{\mathrm{at}}\text{(}\text{¬}\text{→}\text{)}$ indicates that the charges on Si atoms decrease and on V atoms increase in comparison with the charges on free atoms. The magnitude of charge transfer are compared to the results of self-consistent band structure calculation. The observed increase of charge for atom V may be associated with the compression of the 3d-shells of V in V₃Si.     

Beam-foil spectra of the highly ionized sulfur

Spectra of carbon, boron, beryllium, lithium, belium and hydrongen-line for sulfur obtained at an energy of 80 MeV, wherein thirty-four lines have been identified. Analysis of the spectra was based on theoretical results and other experimental data.     

Screening effects in the Ti 2p core level spectra of Ti-based ternary nitrides

The electronic structure of Ti-based ternary nitrides, Ti-X-N, with X = Si, Al or Cr, has been investigated by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. Striking screening effects associated with the decrease of the occupied states at the Fermi level have been observed in the Ti 2p core level spectra of the Ti-Si-N and Ti-Al-N systems with decreasing the Ti content, due to the reduction of the screening ability of conduction electrons. As a consequence of this effect, a strong increase of the ratio between the satellite or “poorly-screened” peak and the main line or “well-screened” peak in the Ti 2p spectra is observed. This behaviour strongly supports the explanation proposed by Porte et al. for the origin of the Ti 2p satellite structure in nearly stoichiometric TiN_x films. Likewise, shifts of the Fermi edge have been observed in the Ti-Si-N and Ti-Al-N systems with decreasing the Ti content. These shifts could be associated with the formation of a nanocomposite structure in which metallic clusters are embedded in an insulator matrix, or just to reflect a metal-to-insulator transition in those ternary systems. Although, the core level and valence band spectra do not allow to univocally decide on this point. The comparative study of the evolution of Ti 2p spectra and of the occupied states at the Fermi level in Ti-Si-N and Ti-Al-N systems suggests that the disappearance of the well-screened peak upon decreasing the Ti content is related not only with the decrease of the occupied states at the Fermi level, but with the formation of isolated metallic clusters embedded in an insulating matrix. The formation of small isolated TiN clusters could change the degree of localization of screening orbitals, therefore promoting the satellite at the expense of the main line in the Ti 2p core level spectra.     

A method for evaluating correlation times for tumbling and internal motion in macromolecules using cross-relaxation rate constants from proton NMR spectra

A method of estimating the correlation times and extent of internal motion of macromolecules using ¹H NMR is proposed. The method relies on measuring the cross-relaxation rate constant between resolved, identified protons separated by a fixed distance, for example 2, 3 protons of tyrosine residues or 4, 5 protons of tryptophan residues in proteins, and the 5, 6 protons of cytosine residues in DNA. For a rigid body, the cross-relaxation rate constant yields directly an estimate of the tumbling time. Deviation of its dependence on viscosity and temperature from expectations for a rigid body allows one to estimate the degree to which internal motions contribute to the relaxation. The method is illustrated for Ribonuclease A and a 20 base pair fragment of DNA corresponding to the trp operator of Escherichia coli. The calculated correlation time of RNAse A is about 8 ns at 298 K, in good agreement with expectations from hydrodynamic measurements. Tyrosine 25 has significant internal motion, characterized by an apparent amplitude of 50–60°, a correlation time of about 5 ns, and low activation energy. The correlation time of the fragment of DNA is about 6.4 ns at 298 K, in agreement with expectations for a rigid rod. The apparent activation energy was 3.8 kcal/mol, close to the value for the dependence of the viscosity of D₂O on temperature. Further, the same result was obtained regardless of the position of the base in the sequence, indicating that bending motions are of small amplitude on the nanosecond time scale for short fragments of DNA.     

薄栅氧化层中陷阱电荷密度的测量方法

提出了一种测量陷阱电荷密度的实验方法,该方法根据电荷陷落的动态平衡方程,利用恒流应力前后MOS电容高频CV曲线结合恒流应力下栅电压的变化曲线求解陷阱电荷密度及位置等物理量.给出了陷阱电荷密度的解析表达式和相关参数的提取方法和结果.实验表明这种方法方便而且具有较高的精度 关键词： 薄栅氧化膜 经时击穿 恒流应力 陷阱电荷密度     

A method for removing etalon oscillations from THz time-domain spectra

We present a simple algorithm for removing or reducing spurious oscillations in the THz spectra which result from secondary reflection peaks in samples or optical elements. The algorithm utilizes the fact that a THz time-domain trace containing secondary peaks can be represented as a convolution of the primary peak and two or more delta functions. The algorithm is applicable for samples which are sufficiently thick that the reflection peak does not overlap with the primary peak, and that do not have strong absorption or dispersion.