原子吸收分光光度法测试技术浅探

为普及和提高原子吸收分光光度法的测试技术,通过长期的测试实践,本文对该技术进行综述,可望能对原子吸收分光光度测试技术有所提高.但其中有些技术,如样品的分解,标准溶液的配制及仪器的灵敏度改善等尚有待更详尽的探讨.     

批判、借助和吸纳——对马克思主义经典作家关于民族主义论述的再认识

马克思主义经典作家在对民族主义持一般反对态度的同时,也对民族主义的进步性做了肯定,对不同性质的民族主义做了区别.根据经典作家的理论设想和世界历史的发展实践,民族主义是实现无产阶级革命和社会主义目标必需的"过渡"性途径.民族主义有着极为鲜明的两重性,既与民族本位、偏狭与排外倾向相通,又为反对压迫和不公提供动员手段,为社会进步提供有效的政治建构和认同.马克思主义经典作家对这个两重性有着清晰的辨别,对其消极性做了严厉的鞭挞和批判,而将它的积极因素在实践上加以借助,在理论上吸纳改造,使其成为马克思主义民族理论的重要内容.马克思主义经典作家对于民族主义的批判、借助和吸纳,既是矛盾的,又是统一的.     

血糖近红外光谱分析中两种常用化学计量学方法的比较

采用主成分回归和偏最小二乘法分别对血糖近红外光谱进行分析,建立数学校正模型。主成分回归模型的相关系数为 0 9294,偏最小二乘法模型相关系数为 0 9998。对两种方法进行比较,确定对血糖近红外光谱分析的方法。     

Covariance analysis and associated spectra for classes of nonstationary processes

In 1951, Cramér introduced a class of nonstationary processes. This broad class of processes contains the important harmonizable and stationary classes of processes. The Cramér class can have additional structure imposed upon it through Cesàro summability considerations. These refined Cramér classes, termed (c,p)-summable Cramér, have recently been considered by Swift (in: M.M. Rao (Ed.), Real and Stochastic Analysis: Recent Advances, CRC Press, Boca Raton, FL, 1997, p. 303). In this paper, the relationship between the (c,p)-summable Cramér classes and the (KF,p) classes of processes introduced by Rao in 1985 is considered. The (KF,p) classes of processes are a generalization of the class of processes considered by Kampé de Feriet and Frenkiel. A continuity theorem for the (KF,p) classes is obtained. This result yields a spectral representation for the (KF,p) classes. Some (KF,p) class processes are shown to arise as the solution to a difference equation obtained from a linear model of a noisy communication channel.     

The absorption distribution and the q-binomial theorem

Approximations for the mean and variance for the absorption distribution are found by means of a transformation of ordinary binomial to Gaussian or q-binomial coefficients.     

Regression methods for high dimensional multicollinear data

To compare their performance on high dimensional data, several regression methods are applied to data sets in which the number of exploratory variables greatly exceeds the sample sizes. The methods are stepwise regression, principal components regression, two forms of latent root regression, partial least squares, and a new method developed here. The data are four sample sets for which near infrared reflectance spectra have been determined and the regression methods use the spectra to estimate the concentration of various chemical constituents, the latter having been determined by standard chemical analysis. Thirty-two regression equations are estimated using each method and their performances are evaluated using validation data sets. Although it is the most widely used, stepwise regression was decidedly poorer than the other methods considered. Differences between the latter were small with partial least squares performing slightly better than other methods under all criteria examined, albeit not by a statistically significant amount.     

Probabilistic modeling of percutaneous absorption for risk-based exposure assessments and transdermal drug delivery

Chemical transport through human skin can play a significant role in human exposure to toxic chemicals in the workplace, as well as to chemical/biological warfare agents in the battlefield. The viability of transdermal drug delivery also relies on chemical transport processes through the skin. Models of percutaneous absorption are needed for risk-based exposure assessments and drug-delivery analyses, but previous mechanistic models have been largely deterministic. A probabilistic, transient, three-phase model of percutaneous absorption of chemicals has been developed to assess the relative importance of uncertain parameters and processes that may be important to risk-based assessments. Penetration routes through the skin that were modeled include the following: (1) intercellular diffusion through the multiphase stratum corneum; (2) aqueous-phase diffusion through sweat ducts; and (3) oil-phase diffusion through hair follicles. Uncertainty distributions were developed for the model parameters, and a Monte Carlo analysis was performed to simulate probability distributions of mass fluxes through each of the routes. Sensitivity analyses using stepwise linear regression were also performed to identify model parameters that were most important to the simulated mass fluxes at different times. This probabilistic analysis of percutaneous absorption (PAPA) method has been developed to improve risk-based exposure assessments and transdermal drug-delivery analyses, where parameters and processes can be highly uncertain.     

SrWO_4晶体中F型色心电子结构的研究

运用相对论的密度泛函离散变分法(DV-Xa)研究了SrWO4晶体中F型色心的电子结构.计算结果表明,F和F+心在禁带中引入了新的施主能级;从施主能级到导带底的电子跃迁能分别是1.858,2.14 eV,这分别与669,581 nm的吸收带相对应.由此说明SrWO4晶体中669,581 nm吸收带起源于晶体中的F和F+心.     

人体对手机辐射吸收剂量的仿真研究

基于时域有限差分法在两种电磁辐射源作用下,对人体组织的局部比吸收量分布进行了数值分析计算,并利用三维数值电磁仿真软件对人体局部的比吸收率分布进行了仿真分析计算。结果表明,人体组织对电磁辐射吸收剂量的分布极不均匀,它与辐射频率、辐射强度、暴露时间以及人体组织的导电率、介电常数等多种参数有关。仿真研究表明减少手机表面电流、避开人体谐振频率可以减少人体的比吸收率。     

Mutability of DNA base pairs: A statistical approach based on linear discrimination

A mutational spectrum measures the frequency of mutations at particular base pairs along a given DNA sequence under the influence of a particular treatment. Such spectra have been measured for several genes, in various organisms and under different treatments. This article presents a method of analysis based on the statistical discrimination between mutable base pairs and stable base pairs. The coefficients of the discriminant function characterize the mutational spectrum induced by a given treatment on a given sequence. These coefficients can be interpreted by the user without specialized statistical knowledge.