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THE use of liquid oxygen as an oxidizer for various fuels in liquid rocket propellent systems is not new. Professor Goddard used liquid oxygen in his rocket experiments and the well known German V‐2 rockets used this material as an oxidizer. However, its effect on non‐metallic materials ordinarily used in rocket systems was not investigated until recent years. This investigation was prompted by phenomena which had been experienced by rocket engine and rocket aircraft manufacturers and by suppliers of the material. It was observed that when some organic materials came in intimate contact with liquid oxygen they became prone to detonation when subjected to certain impact energies. This was undoubtedly due to the formation of unstable organo‐peroxide compounds which when impacted released high levels of energy resulting in an explosion. Specifically, when liquid oxygen was accidently spilled on asphalt and inadvertently stepped on, the asphalt would often explode. Also, leather gaskets immersed in liquid oxygen and subjected to surge impact detonated with disastrous effects.

In systems theory, authors such as Klir, Miller, Yang, Lin and Ma, Backlund, etc. have developed different definitions of the system concept in function of both the type of variables used and the type of connection between variables. The concept of the subsystem, however, tends not to vary substantially from author to author, and this leads to a new system definition based on the subsystem concept, analysing the possible cases of interaction between subsystems and obtaining results for the overall system from an analysis of its subsystems.

Several coefficients, called divergences, have been suggested in the statistical literature to reflect the fact that some probability distributions are “closer together” than others and consequently that it may be easier to distinguish between the distributions of one pair than between those of another. When comparing three biological populations, it is often interesting to measure how two of them “move apart” from the third. Deals with the statistical analysis of this problem by means of bivariate divergence statistics. Provides a unified study, depicting the behaviour and relative merits of traditional divergences, by using the (h,ø), divergence family of statistics introduced by Menéndez et al.

In this paper, we introduce the concept of a supporting set for a general system. We study basic properties of supporting sets for a general system, supporting sets for subsytems of a system, homomorphic images of supporting sets for a system, and supporting sets for free sums and direct sums of systems.

Following Ma, Yonghao and Yi Lin's definition of a mathematical model of general systems in 1987, shows the class of all general systems with relation‐reversion mappings and that of all general systems with relation‐preserving mappings to be productive, co‐productive categories Answers two questions posed in earlier published papers and poses some more questions for solution.

This paper aims to propose a fast and accurate simulation of large-scale induction heating problems by using nonlinear reduced-order models.

A projection space for model order reduction (MOR) is quickly generated from the first kernels of Volterra’s series to the problem solution. The nonlinear reduced model can be solved with time-harmonic phasor approximation, as the nonlinear quadratic structure of the full problem is preserved by the projection.

The solution of induction heating problems is still computationally expensive, even with a time-harmonic eddy current approximation. Numerical results show that the construction of the nonlinear reduced model has a computational cost which is orders of magnitude smaller than that required for the solution of the full problem.

Only linear magnetic materials are considered in the present formulation.

The proposed MOR approach is suitable for the solution of industrial problems with a computing time which is orders of magnitude smaller than that required for the full unreduced problem, solved by traditional discretization methods such as finite element method.

The most common technique for MOR is the proper orthogonal decomposition. It requires solving the full nonlinear problem several times. The present MOR approach can be built directly at a negligible computational cost instead. From the reduced model, magnetic and temperature fields can be accurately reconstructed in whole time and space domains.

In the paper the optimization procedure of a direct current motor with a hybrid excitation has been presented. The excitation system consists of a shunt field winding disposed around field pole and permanent magnet, both acting in parallel. The field distribution in motor for various magnet and field pole dimensions has been determined using finite element method. The flux linkage with the armature winding has been computed. Demagnetizing effect of armature current was taken into account. The optimal permanent magnet and the field pole dimensions, ensuring minimum total cost of purchase and work during assumed period of time were calculated. Motor characteristics e.g. rated torque, rated current, speed regulation limit were used as constraints. In worked up algorithm and computer program Carroll internal penalty function method was used. Some basic suggestions tor design of optimal hybrid excited dc motors with parallel permanent magnet and electromagnetic excitation are given.

I‐V characteristics of GaAs n‐i‐n structures are calculated by considering impact ionization of carriers. Impact ionization at reverse‐biased n‐i junction becomes a cause of steep current rise when an acceptor density in the i‐layer is high. It is shown that an optimum acceptor density exists to keep a good isolation. Photoconduction transients of GaAs n‐i‐n structures are also simulated, and are shown to be strongly affected by existence of n‐i junctions.