N,N'-Diglycidylimides and their polymers

At first new epoxy derivatives, namely glycidylimide compounds, have been prepared using benzyltrimethylammonium chloride as catalyst and epichlorohydrin in excess. Their chemical and physical properties were studied. Spectral data confirmed these new structures. Afterwards new epoxy resins have been synthesized by the reaction of diimides and their glycidyl derivatives in N,N-dimethylformamide. The physical characteristics of the obtained polymers and also their solubilities are reported. Their IR, ¹H- and ¹³C-NMR spectra allowed to confirm the polymer structure. Thermal analysis of these compounds showed their good thermal properties.     

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.     

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.     

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).     

New control concept of anthropomorphic manipulators

In this paper is presented a new control concept of anthropomorphic manipulators for industrial application. A new algorithm is given for finding the dynamic equations of open kinematic chains using a digital computer. The synthesis of the programmed dynamics has been performed via prescribed motion kinematics. The synthesis of the compensating movement level was proposed too, by measuring contact forces between the object and the terminal device. The presented example of a 6 degrees-of-freedom anthropomorphic manipulator illustrates the proposed approach to manipulator control.     

An indirect method for the detection of changes in power network configuration

This paper presents an indirect procedure for determination of power network topology. The procedure applies the methods of state and parameter estimation, using redundant and noisy measurements, and a power system model in the steady state for some known basic network topology. Detection of changes in a network topology related to a basic topology is done by monitoring a suitably selected performance index during the process of static state estimation, while the location of changes requires additional criteria. The paper describes the development of a mathematical algorithm and gives some simulation results obtained on a real power network.     

Statistical study of tram driver accidents

This statistical study considers two basic hypotheses on industrial and traffic accidents the accident proneness theory and the spell theory. The two hypotheses were tested on the basis of a correlation analysis of accident distribution in a group of tram drivers over a five year observation period. Using the chi-square goodness of the test. the analysis showed the negative binomial distribution and the “short” distribution were successfully fitted,while the Poisson distribution significantly differed from the observations. Correlation analysis showed a significant correlation between the number of tram driver accidents over different periods, and that this correlation. although decreasing with an increase of the interval between observation periods, remained significant. The conclusion is that the proneness hypothesis explains more satisfactorily than the spell hypothesis the occurrence of accidents in tram drivers during tlie observation period.     

Allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico

Several experiments were carried out to confirm the allelopathic potential ofAmbrosia cumanensis H.B.K. (Compositae) in a tropical zone of Mexico. The aqueous extracts of leaves and roots inhibited growth of several species used in bioassays. The wash-water of the leaves inhibited some species and stimulated others. The aqueous solutions of soil, in reference to those collected in July, were significant in their general inhibitory action. Decomposition of leaves and roots, in pots where several species were growing, was highly inhibitory to some of the seedlings; microorganisms have a major role in this process.     

Formation of Pb during epitaxial growth of PbS on KCl in a vitreous silica hot wall system

Thin monocrystalline films of PbS grown epitaxially from the vapour on KCl in a vitreous silica hot wall system, present lower specular reflectivity than expected. Electron micrography shows that the surfaces of the films are studded with a multitude of small blobs. They scatter partially the incident light. By electron probe microanalysis and Bragg diffractometry it was found that the blobs are made up of elemental Pb and PbS. As basic lead sulphates were also found on the films the presence of elemental Pb is attributed to the roast reduction reaction. We believe that the silica of the apparatus provides the major part of the oxygen involved in this reaction.