A computer program for searching the best model for describing different experimental systems

An algorithm for searching the best polynomial analytical function for describing different experimental systems is presented. It is based

1. (1)on the generation of all possible analytical functions of a given order, with a given number of terms and with a given number of independent variables, and

2. (2)on the calculation of the parameters of all selected functions using the linear regression method.

To show the ability of the program two different examples are given:

1. (1) searching the best univariate polynomial model, and

2. (2) modelling of the stability of a two-component mixture as a function of three factors.

Determination of arsenic in sediments, coal and fly ash slurries after ultrasonic treatment by hydride generation atomic absorption spectrometry and trapping in an iridium-treated graphite tube

A simple and reliable method for the determination of arsenic in sediment and in coal without sample digestion, based on hydride generation from slurry samples is proposed. After grinding the samples to a particle size of 50 μm, the sample powder was mixed with aqua regia and hydrofluoric acid in an ultrasonic bath for 30 min. After diluting the mixture with hydrochloric acid, the slurry was allowed to stand for 48 h, and an aliquot was used for hydride generation with sodium borohydride. More than 80% of the arsenic was leached to the aqueous phase under these conditions, except for one sediment sample with very high silica content. The generated arsine was collected in a graphite tube, treated with 0.5 mg of iridium as a permanent modifier, and the arsenic determination was carried out by electrothermal atomic absorption spectrometry. The same tube could be used for at least 160 cycles without any re-treatment. The greatest advantage of the method was that only a minimum of reagents and sample handling were required, reducing the risks of contamination and/or analyte loss. However, the addition calibration technique had to be used in order to obtain results within the 95% confidence level for 11 certified reference materials, 5 sediments, 5 coals and one coal fly ash. One certified sediment slurry was spiked with the analyte and the resulting addition calibration curve was used for the analysis of the certified sediments. Similarly, one certified coal was used to obtain the addition calibration curve for the coal and coal fly ash samples. The recoveries of the certified values, except for one sediment, were between 91 and 115%. The limits of detection in the samples were 0.54 and 0.7 μg g⁻¹ for the coal and sediment samples, respectively, obtained for 1 ml of slurry containing 1 mg of sample.     

Field-theoretic approach to second-order phase transitions in two- and three-dimensional systems

We review the physical principles which are at the basis of recent field-theoretic computations of the critical exponents in two- and three-dimensional systems. We concentrate on those points that do not show up explicitly in the more standard-expansion: they must be discussed with care if one uses a perturbative approach at fixed space dimensions (the loop expansion). We present in detail simple computations of the critical exponents, while we summarize the results of longer and more accurate computations.     

碳纳米管在接枝二元胺过程中微结构的变化

通过对酸化的多壁碳纳米管(MWNTs)进行酰氯化, 在碳纳米管表面接枝己二胺. 用红外光谱、热重分析、拉曼光谱和场发射扫描电镜对处理前后的碳纳米管进行分析表征. 结果表明, 经过酰氯活化, 己二胺比较容易被接枝到碳纳米管上. 而且还发现碳纳米管在酸化后形成紧密块状结构, 在接枝胺后重新变得蓬松, 其表观比容甚至大于原始碳纳米管. 从理论上分析了碳纳米管的反应过程, 对碳纳米管在接枝胺过程中微结构的变化机理进行推测, 认为通过接枝, 己二胺插入碳纳米管之间, 改变了碳纳米管之间的相互作用, 使得酸化后因形成氢键而导致的紧密堆砌结构被破坏.     

Effect of the aspect ratio of silicate platelets on the mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber (HNBR)/layered silicate nanocomposites

The role of the aspect ratio of the layered silicate platelets on the mechanical and oxygen permeation properties of hydrogenated nitrile rubber (HNBR)/organophilic layered silicate nanocomposites was investigated. Montmorillonite (MMT) and fluorohectorite (FHT) bearing the same type of intercalant (i.e., octadecylamine; ODA), however, showing different aspect ratio was involved in this study. The dispersion of the layered silicates was assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Increasing aspect ratio (MMT < FHT) resulted in higher stiffness under uniaxial tensile loading. The dispersion state (“secondary structure”) of the organophilic layered silicates reduced dramatically the oxygen permeability of the rubber matrix based on the labyrinth principle. The lowest oxygen permeability was measured for the HNBR/FHT-ODA films in which the layered silicates had the highest aspect ratio. By varying the FHT-ODA volume fraction in the latter compound the mechanical and permeation properties were measured and modelled. It was found that the modified Guth’s and Nielsen’s equations predicted accurately the mechanical and permeation responses, respectively.     

Volumetric properties of the water + ethylenediamine mixture at atmospheric pressure from 288.15 to 353.15 K

Densities of the water + ethylenediamine binary system were measured at atmospheric pressure over the whole range of compositions at temperatures from 288.15 to 353.15 K using an Anton Paar digital vibrating glass tube densimeter. Density increases with water content. The experimental excess molar volume data have been correlated with the Redlich-Kister equation, and partial molar volumes calculated at infinite dilution for each component.     

Ionic liquid–modified cellulosic hydrogels for loading and sustained release of selenourea: an ensuing inhibition of tyrosinase activity

Cellulose-based hydrogel materials were prepared and modified with tannic acid and l-methionine using ionic liquid as the solvent. The gels were prepared to develop a sustained release medium for selenourea (SeU). The drug delivery characteristics of selenourea-loaded cellulose (CSeU), selenourea-loaded tannic acid-modified cellulose (CTSeU), and selenourea-loaded L-methionine-modified cellulose (CMSeU) were investigated in aqueous media and simulated gastric fluid (SGF) media. This modified gel beads have been characterized using field emission scanning electron microscope, X-ray energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, thermogravimetry–differential thermal analysis and swelling properties and compared with those of the unmodified ones. We also investigated the inhibitory effects of SeU released from these gels on the activity of mushroom tyrosinase. Out of all the gel materials, CTSeU showed maximum SeU release both in water and SGF media. However, tyrosinase inhibitory action in PBS medium was comparable for all the three gel materials.     

Static ultrasonic oscillations induced degradation and its effect on the linear rheological behavior of novel propylene based plastomer melts

The ultrasonic degradation of novel propylene based plastomer (DP) melts with different melt viscosities was conducted in a “static” ultrasonic device where the samples were taken from various distances from the tip of an ultrasonic probe. The effects of ultrasonic time, oscillation temperature, ultrasonic intensity and the distance from the ultrasonic probe tip on the degradation behavior of DP melts as well as the ultrasonic degradation effect on the linear rheological behavior of DP melts were studied. The results show that the increase of initial melt viscosity of DP (higher molecular weight) has greater impact on the ultrasonic degradation of DP melt. The molecular weight and intrinsic viscosity of DP decrease with the increase of ultrasonic oscillation time and they approach to a limiting value. The molecular weight distribution of DP increases after ultrasonic degradation. Decreasing oscillation temperature and distance from probe tip and increasing ultrasonic intensity lead to an increase in the degradation of DP melt. The linear rheological behavior measurements of the samples obtained near the ultrasonic probe tip show that ultrasonic oscillations decrease the complex viscosity, zero shear viscosity, viscoelastic moduli, cross modulus, relaxation time and the slope of log G′ − log G″ for DP melts.     

用于测量亚硝酸的长光程吸收光谱仪的研制

This article has been retracted at the request of the authors.     

低压下酞菁裂解法制备定向碳纳米管阵列

在低压条件下以酞菁铁为原料, 采用独立双温控加热系统在石英玻璃基底上气相沉积制备了大面积准直性好和管径均匀的碳纳米管. 利用扫描电子显微镜(SEM/FESEM)和透射电子显微镜(TEM)研究了定向碳纳米管的生长形态和结构. 详细讨论了系统真空度、反应温度、气体流速及氢气和氩气的体积比例等参数对碳纳米管生长的影响, 并测试了该碳纳米管的场发射性能及超电容性能.