On the concentration and determination of plutonium in natural waters by adsorption on MnO2 filters

A new method of analysis of the efficiency of four filters of MnO₂ in series which takes into account the reactions induced in plutonium by the sorbent is described. The system of differential equations describing the behaviour of plutonium in water as it passes through the filters is solved and the parameters of the filters are determined for a best fitting of the solutions corresponding to the experimental uncertainties. The method is checked by numerical simulation and then applied to water solutions with a known plutonium concentration and to some experimental results given by other authors. In all occassions the results are consistent with the possibility of determining the contents of plutonium in sea and continental waters with uncertainties of the order of 10%.     

Preconcentration of trace antimony in tap and sea water on activated alumina. Determination by graphite furnace atomic absorption spectrometry

Summary A method is described for antimony preconcentration based on retention on a column of activated alumina. Recovery is 80% when no pH-control and 4 mol/l HCl as eluent are used. The preconcentration factor is 400. The method was applied to the determination of antimony in spiked tap and sea water. The analytical performance of the method is discussed.     

Improvement of the properties of polyarylate reinforced with liquid crystalline polymers

Blends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.     

General base catalysis in the decomposition of N-Cl-Valine in aqueous solution

This article analyzes the kinetics of the decomposition of N-Cl-Valine in aqueous solution, which is formed rapidly by chlorination of Valine with sodium hypochlorite. A general-base catalyzed process not yet described is reported. The experimental evidence shows two competitive decomposition paths: an unimolecular concerted fragmentation process (k = (1.8 ± 0.1) · 10^?4 s^?1 at 298 K) and the other one is an E2 elimination process whose importance increases with pH and depends on the nature and the concentration of the bases present in the medium. © 1994 John Wiley & Sons, Inc.     

1，4－二氟四苯基苯的合成、结构与构象

借助电子转移催化反应的方法，用电子给予体１，４－二锂四苯基丁二烯将惰性的三溴氟甲烷活化，并与之发生反应，产物１，４－二氟四苯基苯的结构经ＭＳ、ＮＭＲ和Ｘ射线单晶衍射确证，并以分子力学的方法对其进行了构象分析。     

Resolution of binary mixtures of cephalothin and clavulanic acid by using first derivative spectrophotometry

First-derivative spectrophotometric method with a “zero-crossing” technique of measurement has been used for the quantification of two-components mixtures of cephalothin and clavulanic acid. As the absorption bands of these drugs overlap, both direct and derivative spectrophotometric methods have been investigated and evaluated by a rigorous statistical analysis of the experimental data. The first-derivative spectrophotometric method was found to be more accurate, direct and reproducible. Beer's law was valid over the concentration range 2.0–28.0 mg/l for both compounds. The detection limits of cephalothin and clavulanic acid, at a 0.05 level of significance, were calculated to be 0.13 and 0.15 mg/l. The method was applied for determining these antibiotics in mixtures, some of them containing inject-able dosage forms of cephalothin, and so to determine both compounds in saline and glucosed physiological sera.     

Synthesis and Crystal Structure of Di-n-butyltin(IV) Complex with 2-Oxo-propionic Acid (4-Pyridinecarbonyl) Hydrazone

Introduction The studies of diorganotin(IV) complexes are of current interest owing to their wide range of applica-tions such as biocides and homogeneous catalysts in industry.1 In recent years there have been more and more reports on the synthesis, antitumour activities and structural elucidation of various diorganotin(IV) deriva-tives of carboxylic acid.2-5 In particular, people take considerable interest in structural studies of diorgano-tin(IV) complexes of carboxylic acid, because there…     

Formulation of N- and ν-representable density functional theory. V. Exchange-only self-consistent field

The concept of a self-consistent field is developed within the version of density functional theory based on local-scaling transformations. It is shown that in this context there arise two types of consistency: one relating to the charge-consistency within an orbit and another to “orbit jumping.” The latter is analyzed in terms of one-particle equations. The connection with other methods is discussed. © 1992 John Wiley & Sons, Inc.     

用正电子湮没研究高聚物聚甲基丙烯酸甲脂的结构转变与自由体积特性

在20—150℃温度范围内,测量了高聚物聚甲基丙烯酸甲酯(PMMA)中的正电子湮没寿命谱和湮没辐射多普勒展宽谱随温度的变化。两种正电子湮没参数的温度关系均一致反映了高聚物PMMA中的结构变化。108℃和48℃处的变化与玻璃化转变和β相交有关,而本实验发现正电子湮没特征在84℃处出现异常,这可能是此温度下少量自由体积孔洞的连通所致。由实验测得的o-Ps寿命及其相对强度计算了PMMA中自由体积孔洞的尺寸及自由体积分数随温度的变化。     

Local solution for the Kadomtsev-Petviashvili equation with periodic conditions

In this article we prove a local existence and uniqueness theorem for the Kadomtsev-Petviashvili Equation (u _t +u _xxx +uu _x ) _x −u _yy =0) in the Sobolev spaces of orders≥3, with initial values in the same spaces, and periodic boundary conditions. This theorem improves previous results based upon the application of singular perturbation techniques.