Automated derivation of time bounds in uniprocessor concurrentsystems

The successful development of complex real-time systems depends on analysis techniques that can accurately assess the timing properties of those systems. This paper describes a technique for deriving upper and lower bounds on the time that can elapse between two given events in an execution of a concurrent software system running on a single processor under arbitrary scheduling. The technique involves generating linear inequalities expressing conditions that must be satisfied by all executions of such a system and using integer programming methods to find appropriate solutions to the inequalities. The technique does not require construction of the state space of the system and its feasibility has been demonstrated by using an extended version of the constrained expression toolset to analyze the timing properties of some concurrent systems with very large state spaces     

The influence of the ferritic and austenitic phases and of silicon on the Corrosion resistance of alloyed cast steels

The paper deals with the influence of the α/gamma; phase ratio and silicon on the corrosion resistance of low carbon alloyed cast steels in strongly oxidizing media. Electrochemical investigations in 65% HNO₃ + 5g Cr⁶⁺ ions/I showed that none of the four tested cast steels, with γ_R = 100%, γ_R = 75%, γ_R = 50% and γ_R = 0%, achieved a passive state, and that the corrosion process was under cathodic control. Under such conditions the calhodic activation overpotential is considerably greater than the anodic activation overpotential, and, as well as this, the Tafel coefficient for a cathodic reaction has higher values than those which are characteristic for an anodic reaction. The austenitic cast steel is the most resistant to corrosion, since for the corrosion process to take place the greatest activation energy is needed. The results of investigations of corrosion resistance in 12M HNO₃, at 115°C, for 240 hours, confirmed the results of the electrochemical measurements and the predominant role of the austenitic cast steel with γ_R = 100%. By means of AES analysis it was found that the good resistance to corrosion of such a cast steel is based on the building up of a thin mechanically-protecting barrier, which mainly consists of silicon.     

Carbon fibre composites based on polyimide/silica ceramers: aspects of structure-properties relationship

Polyimide/silica ceramers, based on the products of the hydrolysis of tetraethoxysilane (TEOS) and a commercial poly(amic acid) solution, were used to fabricate unidirectional carbon fibre composites, which were subsequently evaluated with respect to thermal and mechanical properties. There is evidence to suggest that the silica component of these ceramers is present as dispersed discrete particles at low silica concentration (i.e. 7 wt%) and as fine interconnected domains trapped within the polyimide matrix at higher silica content (i.e. 14 wt%). The dimensions of the silica domains were in the region of 7–20 nm. Carbon fibre composites produced from ceramer solutions (CF/ceramers) were found to exhibit lower thermal expansion and a greater retention of flexural and interlaminar shear properties at elevated temperature than the corresponding polyimide-matrix composites (CF/polyimide). The properties of CF/ceramers were generally better for systems containing the higher amount of silica and were improved further by lowering the pH value of the precursor ceramer solution. This is believed to have resulted from the enhanced fluidity of the ceramer gel within the pre-impregnated fibres, giving rise to a higher packing density of the fibres and a more homogeneous distribution of fibres. CF/ceramers were also found to exhibit a better thermal oxidative stability at 350°C than the corresponding CF/polyimide, although a substantial amount of porosity developed in the case of ceramers with the higher silica content.     

Feedback Insertion-Deletion Codes

Problems of Information Transmission - A new problem of transmitting information over the adversarial insertion-deletion channel with feedback is introduced. Assume that the encoder transmits $$n$$...     

Microinhomogeneity of deformation and mechanical properties of steel in static and impact tests

The article presents the results of the investigation of the mechanical properties and microinhomogeneity of deformation of steel in dependence on its structure. A dependence of the characteristics of ductility and of impact toughness on the level of the microinhomogeneity of deformation is established. The change of ultimate (tensile) strength _u corresponds to the change of microhardness which serves as indirect characteristic of the strength properties of microvolumes. It is shown that impact toughness is a characteristic sensitive to the manifestation of microinhomogeneity of deformation, and that it changes in dependence on its level more than the static characteristics. The obtained results make it possible to choose the optimal structure of the metal.Translated from Problemy Prochnosti, No. 1, pp. 120–122, January, 1990.     

Hot corrosion ofα-SiC ceramics by V2O5 melt

The corrosion behaviour of-SiC in V₂O₅ melt has been investigated at elevated temperatures. The corrosion products on the surface of the specimen are removed using HF. The morphologies are also examined. From the observations of bubble formation in the scale and the temperature dependence of the corrosion rate, a kinetic mechanism is proposed. Based on the consistency of the plotted data with the proposed equation and high values of surface reaction rate constant, a diffusion controlling process has been developed.     

Vibratory comminution of A12O3 powders

Translated from Poroshkovaya Metallurgiya, No. 8(332), pp. 6–9, August, 1990.