Positron lines from subcritical heavy ion-atom collisions

Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ _u =Z ₁+Z ₂ being smaller thanZ _u =172. Each collision system, studied,²⁰⁸Pb +²⁰⁸Pb(Z_u=164),²³⁸U+¹⁸¹Ta(Z_u=165), and²³⁸Au(Z_u=171), exhibits the emission of two positron lines withZ _u -independent c.m. energies of ～ 258 keV and ～ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee ⁺-lines rises with a high power ofZ _u (ocZ _u ²²), which is comparable to theZ _u ²⁰-dependence for the collision induced positrons.     

Electrons from quasi-atoms formed in heavy-ion collisions

Electrons emitted in heavy-ion collisions of oxygen and sulfur projectiles with heavy targets were measured. Electron energies up to five times the K-shell binding energy of the target atom were observed. The high-energy part can be explained well within the framework of the Born approximation using relativistic electron wave functions for the united atoms. It is argued that the high-energy shape of the spectra is directly related to the form factor of inner shell electrons of the united atoms.     

The reaction of diazomethane with double bonds—I Direct methylation of trisubstituted ethylenes

The reaction of -carbomethoxy-γ-benzylidenebutenolide with diazomethane has been studied, and the β-methylbutenolide structure of the resulting product established through degradative and synthetic work. Extension of this direct C-methylation to other related butenolides is presented. Hydrogenation of enol lactones is discussed in some detail.     

Local completeness and Pareto optimization

In this paper we study the Pareto optimization problem in the framework of locally convex spaces with the restricted assumption that only some related sets are locally complete.     

Process Analytical Chemistry: Applications of Ultraviolet/Visible Spectrometry in Environmental Analysis: An Overview

Abstract

Process analyzers based on the selective absorption of the ultraviolet (UV) and/or visible (VIS) radiation provide an on-line monitoring highly reliable of the composition and the industrial process control.

This review provides information about the technological advances in this area and its industrial applications, especially environmental applications.     

Generalised H-point standard addition method for the isolation of the analyte signal from the sample signal when coelution of unknown compounds occurs in liquid chromatography.

The generalised H-point standard addition method (GHPSAM) is proposed for isolating the analytical signal of an analyte from the signal of an unknown sample. Samples containing two and three coeluting compounds have been analysed. The accuracy of the predictions depends on the shape of the analyte and interferent spectra but not on the degree of chromatographic overlap. This methodology involves the location of linear intervals for the unknown interference spectrum from the spectrum of the sample. Once the linear interval has been found the selection of three wavelengths within the interval will allow the cancellation of the signal of the unknown interferent. The method has been applied to the determination of diuretics, amphetamines and phenols in water.     

Synthesis,Characterization, and Dissolution of Biomorphic Ceramics: Determination of Metal Ions

Converting biological structures into ceramic materials has recently received increasing interest. In the current paper, wood templates (oak and beech) with a unidirectional pore structure have been used as the carbon source. We have synthesized two new biomorphic ceramic materials from oak and beech woods and Si infiltration. After the material characterization, we have optimized the sample dissolution by acid attack in an oven under microwave irradiation. Experimental designs were used as a multivariate strategy for the evaluation of effects of varying several variables. The optimization was performed in two steps using factorial design for preliminary evaluation and a Draper–Lin design for determination of the critical experimental conditions. Five variables (time, power, volume of HNO₃, volume of H₂SO₄, and volume of HF) were considered as factors, and response was considered as the concentration of different metal ions in the optimization process.     

A practical procedure for the removal of the phenylethanol moiety from phenylglycinol-derived lactams

Chiral non-racemic bicyclic lactams derived from phenylglycinol have been appointed as key building blocks for the preparation of enantiopure nitrogen compounds. The removal of the chiral inductor leading to substituted piperidones by using air or oxygen in basic media is presented.     

Separation preconcentration method for platinum and rhodium from environmental samples using a chelating resin

A method of determining trace levels of platinum and rhodium in different samples was investigated. The method involves separation and preconcentration of the platinum and rhodium from the matrix by flow injection (FI) on-line coupled with electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background correction. Platinum and rhodium were adsorbed on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). The sorbed metals were directly eluted with nitric acid into the graphite furnace and determined by AAS.