Tube-shaping unit — A way of improving the quality of shaped tubes

Lenin Dnepropetrovsk Pipe Plant. Translated from Metallurg, No. 8, p. 39, August, 1989.     

Synthesis and characterisation of copolyesters from poly(ethylene terephthalate) and poly(hexamethylene terephthalate)

Copolyesters containing poly(ethylene terephthalate) and poly(hexamethylene terephthalate) (PHT) were prepared by a melt condensation reaction. The copolymers were characterised by infrared spectroscopy and intrinsic viscosity measurements. The density of the copolyesters decreased with increasing percentage of PHT segments in the backbone. Glass transition temperatures (T_g). melting points (T_m) and crystallisation temperatures (T_c) were determined by differential scanning calorimetry. An increase in the percentage of PHT resulted in decrease in T_g, T_m and T_c. The as-prepared copolyesters were crystalline in nature and no exotherm indicative of cold crystallisation was observed. The relative thermal stability of the polymers was evaluated by dynamic thermogravimetry in a nitrogen atmosphere. An increase in percentage of PHT resulted in a decrease in initial decomposition temperature. The rate of crystallisation of the copolymers was studied by small angle light scattering. An increase in percentage of PHT resulted in an increase in the rate of crystallisation.     

“Metallisation” of oxide surfaces observed by in situ high-resolution electron microscopy

Intense irradiation (25–40 A/cm²) at intermediate energy (400 keV) has been found to cause “metallisation” of tungsten oxide and titanium niobate crystal surfaces. The possible mechanisms and the likely consequences for high-resolution imaging of clean oxide surfaces are briefly discussed.     

Half-bridge inverter using 4H-SiC gate turn-off thyristors

This paper reports on the first demonstration of a half-bridge power inverter constructed from silicon carbide gate turn-off thyristors (GTOs) operated in the conventional GTO mode. This circuit was characterized with input bus voltages of up to 600 VDC and 2 A (peak current density of 540 A/cm²) with resistive loads using a pulse-width modulated switching frequency of 2 kHz. We discuss the implications of the thyristor's electrical characteristics and the circuit topology on the overall operation of the half-bridge circuit. This work has determined the conservative critical rate of rise value of the off-state voltage to be 200 V/μs in these devices     

Three-phase flash and distillation

A mixed K-value model allows existing computer programs for the simulation of vapor-liquid equilibrium stages to be used for three-phase vapor-liquid-liquid systems. The mixed K-value model has been implemented with a minimum effort into the Badger General Material Balance flow-sheeting program. Good convergence has been obtained with the mixed K-value model for a number of systems. A comparison is made with published literature [1, 2], showing excellent results with this generally applicable and easy-to-use method.     

Comparison of Solutions of the Problems of Elasticity Theory for Different Near-Boundary Elements

We consider three types of near-boundary elements: curvilinear quadrangles and families of arcs and points, and their application to a two-dimensional problem of the static theory of elasticity with boundary conditions in displacements. The comparison of the theoretical and numerical aspects of the obtained solutions is performed. It is shown that the accuracy of evaluation of the components of the vector of displacements increases in the following cases: in the case of complete quantization of the near-boundary region (but not in the case of its partial quantization or quantization with overlapping), in the case where the numbers of arcs and points increase, and in the case of simultaneous application of different types of near-boundary elements (specifically, quadrangles and families of arcs).     

The first accurate measurement of systolic and diastolic bloodpressure

Poiseuille, known for his law of fluid flow, which is the analog of Ohm's law, introduced the units (mmHg) by which we measure blood pressure by using the mercury manometer, which he described in his medical school thesis in 1828. For 50 years, mean blood pressure was all that could be measured because of the long response time of the mercury manometer. It is true that the height of the mercury column displayed pulsatile oscillations, but their amplitude was much less than that of pulse pressure. It is interesting to note that the slowly responding mercury manometer was made to display first systolic then diastolic pressure by means of an ingenious device that contained two oppositely directed check valves. It took from 1828 to 1903 for high-fidelity graphic recordings of blood pressure to appear in which systolic and diastolic pressures were believable. However, systolic and diastolic pressures were measurable since 1878 when Golz and Gaule created their ingenious valved device that permitted use of the slowly responding mercury manometer to display these pressures accurately