Application of composites to impact energy absorption

The sleeve, conical simple composite elements and polymer foam filled composite conical element behaviour during failure are presented and discussed. The impact energy in these elements is absorbed in progressive fracture process. Possibilities of energy absorption panels – the great structures made from simple elements in a certain military and civilian field are demonstrated.     

Stabilization of singular 2-D continuous-discrete systems bystate-feedback controllers

Necessary and sufficient conditions are established for the existence of a solution to the stabilization problem for singular two-dimensional (2-D) continuous-discrete linear systems. A procedure is presented for designing a state-feedback controller such that the closed-loop system is asymptotically stable, and its response is impulse-free     

Changes in structure of psoas major and minor and semitendinosus muscles of calves, heifers and cows during post-mortem ageing

Changes occurring during post-mortem ageing in structure of psoas major and minor (PM) and semitendinosus (ST) muscles of calves, heifers and cows were observed. Samples from muscles taken 3 h after slaughter and after 6 and 12 days of storage at the temperature of 4?°C were analysed using light and transmission electron microscopy. Three hours after slaughter muscle fibres were close to each other and sarcomeres showed normal structure of A- and I-bands, M-lines and Z-disks. The space between myofibrils and sarcolemma and also between single myofibrils in muscle fibres increased during storage. Structure of sarcomeres underwent continuous degradation, length of sarcomeres increased due to enlargement of I-bands accompanied by Z-disk degradation. During ageing structural changes in myofibrils took place faster, were more intensive in muscles of younger animals and were more extensive and faster in PM than in ST muscles.     

X-ray scattering investigations of acrylonitrileethylene oxide block copolymers

Wide angle (WAXS) and small angle (SAXS) X-ray scattering studies are reported on block copolymers of acrylonitrile with ethylene oxide. A distinct structural similarity between the copolymers and acrylonitrile homopolymer has been found. Considerable porosity of the copolymers has been shown. The porosity very largely governs the scattering power. It was found that the pores are three dimensional “particles” (scattering exponent α = 4), probably with smooth surfaces (surface fractal dimension d_s = 2).     

Dynamic Characteristics of Solids Transportation in Rotary Dryers

An original method was proposed for the determination of the mean residence time in a continuous dryer, based on the step-change in the solids feed rate. The method has been validated through experiments performed in a pilot-scale rotary dryer. The effect of the solids flow rate, gas flow rate, dryer rotation speed, and dryer slope was quantified. Several design correlations to predict the residence time in rotary dryers were critically evaluated, and a new, more accurate correlation was derived.     

Chemistry and application of organic isocyanates,IX. Conversion of tolylene-2,4-diisocyanate into urethane derivatives by means of heptane-1,4,7-triol

Investigations on the conversion of tolylene-2,4-diisocyanate (2,4-TDI or TDI) with heptane-1,4,7-triol 1,4,7-HPT or HPT) at 55–85°C and various molar ratios of starting materials are described. By means of mass spectroscopic analysis and gel permeation chromatography, molecular weights of six oligomers and their percent contents in the products have been estimated. Moreover, a scheme of the formation of all prepared isocyanate prepolymers has been proposed. It has been shown, that apart from oligomers having the structures resulting from the reaction of 1,4,7-HPT with the isocyanate group in the position “4”, reaction products contained oligomers, which confirmed the reactivity of isocyanate group in the position “2”, too.     

Freeze-fracture electron microscopic and low temperature X-ray scattering studies of the effect of cryofixation upon serum low density lipoprotein structure

We report here a correlated X-ray diffraction and freeze-fracture electron microscope study of the effects of several cryofixation procedures upon human serum low density lipoprotein (LDL₂) structure. Only when the LDL₂ solutions contained 75%, by weight, glycerol were the room temperature and post cryofixation low temperature LDL₂ X-ray scattering curves indistinguishable from one another. Other cryofixation procedures, slow or rapid, with or without glycerol, resulted in differences between the room temperature and low temperature LDL₂ X-ray scattering curves, in part due to the effect of quenching upon the solvent. Freezeetching electron microscopy of the slowly cryofixed LDL₂ showed marked aggregation of the particles and an unusual morphological appearance. In contrast, after rapid cryofixation or cryofixation in the presence of glycerol, freeze-etch electron microscopy revealed well-isolated particles which had a knobby morphology. The results demonstrate that under certain conditions (in the presence of 75% glycerol) cryofixation results in minimal, if any, structural alteration of, at least, the LDL₂ lipid moiety. Further, this study underlines the more general conclusion that any high resolution structural study employing a cryofixation step must be interpreted with caution and the effect of cryofixation upon the sample structure need be evaluated by independent means.     

Determination of copper in water by means of chalcocite copper ion-selective electrode

The possibility of determination of copper in natural waters was tested by direct potentiometry with chalcocite copper sensitive ion selective electrode. This can be carried out for the copper concentration down to 6 μg l⁻¹ when the standard additions procedure is used. The electrode characteristics was investigated and as a medium was proposed a TFB solution containing Tris, potassium fluoride and potassium nitrate. However at the extreme low concentrations of copper the water samples after addition of TFB should be heated to boiling. In these conditions the accuracy of determination for the average of five measurements is not worse than 25%, and precision is of the order of 20%.     

Analytical function for lidar geometrical compression form-factor calculations

A simple model of image formation in a Newtonian telescope was used for calculating an analytical formula, that describes the geometric compression form factors of coaxial and biaxial lidars. Calculations were successfully validated by comparison with real measurements, confirming the accuracy of our approach. The need for different alignment of coaxial and biaxial systems to increase the overlap between the lidar emitter and receiver is also discussed.