Curing of unsaturated polyester resins with low exotherm peak

The curing behavior of an unsaturated polyester resin with low exotherm peak was studied by a standard procedure and by differential scanning calorimetry (DSC). A copper salt and α-methylstyrene were used as the polymerization retarders. The influence of the retarders on the exotherm peak temperature, gelation time, exothermic heat and the polymerization kinetics was investigated.     

Extracts of phenolic compounds from seeds of three wild grapevines-comparison of their antioxidant activities and the content of phenolic compounds

Phenolic compounds were extracted from three wild grapevine species: Vitis californica, V. riparia and V. amurensis seeds using 80% methanol or 80% acetone. The total content of phenolic compounds was determined utilizing the Folin-Ciocalteu’s phenol reagent while the content of tannins was assayed with the vanillin and BSA precipitation methods. Additionally, the DPPH free radical scavenging activity and the reduction power of the extracts were measured. The RP-HPLC method was applied to identify the phenolic compounds in the extracts, such as phenolic acids and catechins. The seeds contained large amounts of tannins, catechins and gallic acid and observable quantities of p-coumaric acid. The total content of phenolic compounds and tannins was similar in the extracts from V. californica and V. riparia seeds. However, the total content of total phenolic compounds and tannins in the extracts from V. californica and V. riperia seeds were about two-fold higher than that in the extracts from V. amurensis seeds. Extracts from seeds of the American species (V. californica and V. riparia) contained similarly high concentrations of tannins, whereas extracts from seeds of V. amurensis had approximately half that amount of these compounds. The content of catechin and epicatechin was similar in all extracts. The highest DPPH^• anti-radical scavenging activity was observed in the acetonic and methanolic extracts of V. californica and V. riparia seeds— while the acetonic extract from the V. californica seeds was the strongest reducing agent.     

Modelling the movement of a two-link manipulator

An algorithm for optimizing the control signal for simple movements of a two-link manipulator with four degrees of freedom is described. Based on the typical movement and functions of upper human extremities, the manipulator (so-called anthropomorphic manipulator) is composed of two links. The motion of the links is developed by four driving motors. The mathematic model is based of the Lagrange equations of the IInd king. The minimization of the time of movement with initial limitation of accuracy is obtained and the error of the final position is minimized without changing the time-optimal criterion. The relations connected with minimalization of both quality factors are considered. At the same time, the algorithm optimizes the torque distribution between the actuators which drive each link of manipulator. As well the manipulator as its activity are modelled on the digital computer. The results of the computer simulation of the algorithm, and the modelling of the time and accuracy optimal control, are presented.     

Halogenated polyethylenes as electron-sensitive resists

Irradiation of a layer of halogenated polyethylene with an electron beam at 10-kV accelerating potential brings about crosslinking of brominated and chlorobrominated polyethylenes, but the chlorinated polyethylenes undergo either crosslinking or degradation, depending on the electron charge delivered. The limiting charge value which separates these two effects was found to be ca. 1 × 10^?3C/cm². The minimum useful dose was found to increase in the order brominated, chlorobrominated, chlorinated polyethylene.     

Phosphate inactivation with iron chloride during sediment resuspension

The present study undertook laboratory and in situ experiments in two hypertrophic lakes in order to determine the possibilities for the effective PO₄ precipitation by means of FeCl₃, applied directly to organic sediments (at a specific depth) previously subject to resuspension. The study also aimed to test, modify and improve a device constructed previously. This made the direct application of FeCl₃ to organic sediments possible, while generating resuspension in the surface layer of sediments to a specified thickness. The results of both laboratory and field experiments, and tests of the prototype device, showed that linking a dosage of FeCl₃ with the initiation of controlled resuspension led to a decrease of seven-fold in the concentration of PO₄ in interstitial water, and changed other physical and chemical parameters in the water only slightly. The effectiveness of PO₄ precipitation relied mostly on initial conditions in the interface of water–organic sediment phases, and especially on the sorption capacity of sediments for phosphates, on the gradient of PO₄ concentration, and on the concentration of oxygen in the layer of water above the sediment. It could be an effective method of over-eutrophied lakes reclamation, and an alternative to the expensive removal of sediments.     

Invariants and paradigms of concurrency theory

We introduce a new invariant semantics of concurrent systems which is a direct generalisation of the causal partial order semantics. Our new semantics overcomes some of the problems encountered when one uses causal partial orders alone. We discuss various aspects of the new invariant model. In particular, we outline how the new invariants can be generated by I-safe inhibitor Petri nets.