Investigation of the extraction equilibria in the system hexachloridorhenate(IV)-neotetrazolium chloride-dichloroethane-water

The neotetrazolium hexachloridorhenate(IV) (NTReCl(6)) has been synthesized and its composition checked. The optimum conditions for the extraction of NTReCl(6) with dichloroethane have been established. The recovery factor for one-fold extraction is R = 74%. The distribution constant, K(D), extraction constant, K(ex), and ion-association constant, beta, have been determined. Neotetrazolium chloride was found to be suitable reagent for extraction-spectrophotometric determination of rhenium(IV) ((NTReCl(6)) = 3.42 +/- 0.20 x 10(4)M(-1) cm(-1)).     

A new approach to the study of ion transport processes by an in situ radiotracer method based on measuring intensity changes and energy spectrum alterations of β-radiation

A new approach for the study of ion transport by an in situ radiotracer method is presented. The method is based upon the measurement of the intensity and energy spectrum change of -radiation during the penetration of labeled species. The applicability of the radiotracer technique is detailed through the measurement of the transport of labeled chloride ions into a PERMAPLEX-A20 anion exchanger membrane. The proposed method is applicable to in situ monitoring of the motion of ions in the membrane (or adsorbent).     

Influence of substituents on positron annihilation in styrene copolymers

Results of angular correlation of annihilation radiation (ACAR) and positron annihilation lifetime (PAL) measurements are presented for five styrene copolymers: poly(co-styrene-phenylmaleimide) and its three derivatives with chlorine as well as for one with the OH group substituted at the benzene ring. It occurs that the chlorine substituted at three different positions at the benzene ring poly(co-styrene-o (or-m,-p)-chlorophenylmaleimide) inhibits the formation of the positronium to different extent. The greatest effect is observed in case of the chlorine atom substituted at the benzene ring at the ortho-position towards the nitrogen atom. The two long lifetimes (₃ and ₄) observed in the lifetime spectra are connected with the bimodal distributions of the free volume radius in the samples.     

Recent results from the TCV tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B _tor1.46T,I _p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s^–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors ( _tor aB/I _p) up to two and densities up to 2.25×10²⁰m^–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×10²⁰m^–3 have been obtained in elongated D-shaped plasmas with 360 kAI _P600 kA.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique.     

Hydrolysis of 2-aminoethanethiolsulfate ions

The kinetics of the acid catalyzed hydrolysis of 2-aminoethanethiolsulfate (AETS) ions were investigated. The dependence of the hydrolysis rate constant on acidity and temperature was determined. The hydrolysis rate equation can be expressed as where H_o is the Hammett acidity function. The rate constant, k, can be expressed as The pK_a's for the compound were measured and literature value of pK_a was found to be in error. The values determined in this study are pK_a1 < ?0.5 and pK_a2 = 9.1 ± 0.1. General acid catalysis of the hydrolysis reaction was found not to proceed to a significant degree. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Determination of chromium in aquatic environment by substoichiometric thermal neutron activation analysis

Chromium has been determined in environmental samples. The method described here involves the irradiation of environmental samples and a g quantity of standard with thermal neutrons at the self-serve position in the CIRUS reactor, followed by dissolution of the sample and standard in the presence of a milligram amount of carrier. Both the sample and the standard are subjected to substoichiometric extraction under controlled experimental conditions with alizarin into cyclohexane. An aliquot of the organic phase was counted on a gamma-ray spectrometer. The concentration of Cr in water samples from Bombay and Karad City, and the accuracy, precision and sensitivity of the method are discussed.     

On invexity-type nonlinear programming problems

In this paper, we propose a new class of nonlinear programing, called SFJ-invex programming. The optimality characterization shows that a problem is SFJ-invex if and only if a Fritz John point together with its multiplier, is a Fritz John saddle point of the problem. Under any constraint qualification assumption, a problem is SFJ-invex if and only if a Kuhn-Tucker point together with its multiplier is a Kuhn-Tucker saddle point of the problem. Furthermore, a generalization of the SFJ-invex, class is developed; the applications to (h, )-convex programming, particularly geometric programming, and to generalized fractional programming provide a relaxation in constraint qualification for differentiable problems to get saddle-point type optimality criteria.The author wishes to thank the referee for helpful comments.     

Evaluation of partition measurements in liquid-liquid segmented flow

The different configurations possible for an FIA extraction system for partition measurements have been tested and the corresponding evaluation formulae based on determinations at different phase flow ratios, verified. Increased flexibility results from the possibility of using samples dissolved in either aqueous or organic phase. Choosing the best configuration in every case makes it possible to extend the range of measurable conditional partition constants without excessive losses in precision.     

The effects of media properties on the horseradish peroxidase-catalyzed fluorogenic reaction

The effects of media properties including buffers, acidity, solvents and surfactant on horseradish peroxidase-catalyzed fluorogenic reaction were investigated. The results showed that the so-called non-fluorescent hydrogen donors were in fact fluorescent. There existed an acid—base equilibrium in the fluorescent dimer product. For p -hydroxyphenylpropionic acid, a pK_a value of 8.0 for the product was obtained from its titration curve. The product fluorescence increased with higher pH, however, a longer time was needed to reach the reaction equilibrium due to the pH mismatch problem. Cationic micelles cetyltrimethylammonium bromide and cetyltrimethylammonium chloride could reduce the pH mismatch and offered a way to further increase the determination sensitivity. Finally, a micelle-enhanced flow-injection analysis of horseradish peroxidase is suggested.     

Strong converse inequality for Kantorovich polynomials

For the Kantorovich polynomial approximationK _n (f, t), 1<p≤∞, we prove that, for somem, This equivalence includes a strong converse inequality of type B.