Photochromic polymers

Summary Two soluble photochromic polymers containing 1-(ß-hydroxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2-indoline] bound on a variously long side chain were prepared. It was found that the discolouration process depends on the length of the side chain to which the photochromic centre is bound.     

Comparison of different modes of excitation in X-ray emission spectroscopy in the detection of trace elements in coal and coal ash

Three different modes of sample excitation in X-ray emission spectroscopy were used in trace element analysis of coal and coal ash: proton beam, Mo X-ray tube and radioactive sources ⁵⁷Co and ¹⁰⁹Cd. The results of analysis are presented and methods and their possibilities are compared in order to indicate the most appropriate technique for the particular purpose.     

Mobility of holes in p-type silicon determined by the self-consistent method

The mobility of majority carriers is calculated in p-type silicon in the impurity concentration range from 10¹⁶ to 10²⁰ cm^?3. Taking into account the complexity of the band structure of holes and using the self-consistent model development earlier for electrons, the value of the Fermi energy and the screening length is determined. The following scattering types are considered: scattering by acoustical phonons, scattering by non-polar optical phonon and scattering by ionized impurities. The influence of interband transition of heavy and light holes on the total relaxation time is analysed. It is shown that it does not lead to essential changes in mobility. The obtained results are compared with experimental results and satisfactory agreement is found.     

On the use of pulse NMR techniques for the study of cement hydration

The application of pulse NMR to the study of hydration of cement and its constituents is discussed. The quantity of adsorbed water in hydrated samples can be most easily determined by measuring the proton free induction decay signal, whereas the rates of hardening and hydration can be best followed by measuring the proton spin-lattice and spin-spin relaxation times. The use of multiple pulse high resolution NMR in solids techniques is helpful in separating the H₂O and OH-group signals whereas ²⁷Al quadrupole coupling and spin-lattice relaxation may as well contribute to our understanding of the structure and hydration of cement.     

An approach to the evaluation of electromechanical transient processes in power systems

The paper presents an approach to the evaluation of electromechanical transient processes in power systems. On the basis of identification of the physical properties of the system considered, for an adequately chosen time interval, quasilinearization and decomposition of the original system of nonlinear differential equations into subsystems is performed. A linear transformation is introduced which transforms the state matrix of the sub-systems into diagonal form. These simplifications enable the use of numerical integration schemes based on difference state equations, which have an elementary form. As a result, a model is formed which is very suitable for numerical treatment. The integration is performed without numerical instability, quickly and effectively, with the desired simulation accuracy, and with low memory requirements.     

Dynamic tear tests of carbon weldable steels

For determining the crack arrest temperature of structural weldable steels of mass production, it is convenient to use the dynamic tear test because of its simple and low cost application using drop weight testers or pendulum testing machines. The dependence of the dynamic tear energy on temperature can in fact represent the curve of the crack arrest temperatures. The energy/temperature results have to be transformed into the nominal stress vs. temperature coordinates to permit a better review and simpler application. This work describes two methods of making such transformations and shows some results acquired with carbon weldable structural steels.     

High conversion polymerization of α-methylstyrene with maleimide at different monomer-to-monomer ratios in the feed

Summary High conversion polymerization of -methylstyrene (-MeSt) with maleimide (Ml) was performed in Calvet differential microcalorimeter under different monomer-to-monomer ratios in the feed using AIBN as initiator. From the calorimetric curve it was observed that in the presence of an excess of Ml, alternating copolymer is quantitatively formed prior to the formation of poly (Ml).