§ 149. Present Perfect часто употребляется при составлении краткой аннотации, предшествующей статье (Abstract), и кратких выводов, помещаемых после статьи (Summary)). Например:

Abstract

The compounds N-allyl-a-pyrrolidone, N-allyl-e-caprolactam, and N-allyl-a-piperidone have been synthesized and described. In а study of the polymerization of N-allyl-pyrrolidone and N-allylcap-rolactam in the presence of free radical initiators it was found that N-allylactam is not activated by benzoyl peroxide, but with 5—10% azoisobutyrodinitrile it undergoes stepwise polymerization to produce low yields of the dimers and trimers. The copolymerization of N-allylpyrrolidone with vinyl acetate, methyl methacrylate, and methyl acrylate has been investigated.

11*

Summary

The ultraviolet, infrared, and luminescence spectra of ethyl-cellulose preparations with varying carboxyl group contents have been investigated. The luminescence spectra and intensities have been found to change as the preparations are irradiated with ultraviolet light. The changes are particularly marked in the initial steps of irradiation allowing one to determine the very first stages of degradation of ethyl cellulose molecular chains. Light sensitivity has been shown to increase with the carboxyl content of the ethylcellulose specimens. Neutralization of the groups by Pd and Na cations leads to light stabilization of the compounds. It has been suggested that the presence of carboxyl groups in the ethyl cellulose compounds accelerates the ultraviolet-induced photochemical reactions. This is in accord with the earlier assumption of the part played by carboxyl groups in the thermooxidative degradation of ethylcellulose.

Abstract

Complex formations between dimethyl sulphide, diethyl sulphide, and tetrahydrothiophen and niobium pentachloride and pen-tabromide, and tantalum pentachloride, pentabromide, and penta-iodide has been studied. The following crystalline 1 : 1 complexes have been isolated, and their compositions established by analysis and vapour-pressure measurements.

Summary

The specific gravity of fibers of polyacrylonitrile and chlorinated poly vinyl chloride (64% Cl) subjected to stretching and thermore-laxation has been determined by the flotation method. The results have been interpreted in terms of changes in the molecular packing density which has been shown to depend on both orientation and ther-morelaxation. A theoretical calculation has been made of the specific gravity of a number of polymers.

1 Примечание. В Present Perfect Tense обычно стоят те глаголы, которые указывают на конкретный, полученный авторами, результат. Описание эксперимента и других явлений в основном передается простыми формами Indefinite.

§ 150. Present Perfect часто используется в н а ч а-л е _l(b вводной части) статьи. В отличие от его функции в аннотации или кратких выводах (см. § 149), в данном случае Present Perfect указывает на то, что уже сделано другими раньше, и подводит к теме, исследуемой самими авторами.

Например:

164

Introduction

Ever since the discovery by Szilard and Chalmers, in 1934 that chemical reactions can result from the consequences of nuclear processes, the attempted elucidation of the chemical consequences of radiative neutron capture has been the object of much experimental effort. A mechanistic approach to hot atom chemistry has appeared comparatively recently. No generalization has yet appeared which provides a unifying rationale of all currently available data. Several models, for example physical impact, epithermal reactions, random bond fragmentation and the displacement spike, which emphasize physical considerations, have been suggested. Models stressing the importance of chemical environment have also appeared.