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This paper deals with heterogeneous queues where servers differ not only in service rates but also in operating costs. The classical optimisation problem in queueing systems with heterogeneous servers consists in the optimal allocation of customers between the servers with the aim to minimise the long-run average costs of the system per unit of time. As it is known, under some assumptions the optimal allocation policy for this system is of threshold type, i.e., the policy depends on the queue length and the state of faster servers. The optimal thresholds can be calculated using a Markov decision process by implementing the policy-iteration algorithm. This algorithm may have certain limitations on obtaining a result for the entire range of system parameter values. However, the available data sets for evaluated optimal threshold levels and values of system parameters can be used to provide estimations for optimal thresholds through artificial neural networks. The obtained results are accompanied by a simple heuristic solution. Numerical examples illustrate the quality of estimations.

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The effect of Cu addition on structure and mechanical properties of the gray cast iron is studied. Copper is showed to affect the graphitization process. Copper content increase up to 6 ... 7 wt. % reduces the depth of the chill layer.With further increase of coppercontent the alloys tendency to chilling effectincreases.When the cast ironcontains from 0 to ~ 7% Cu, inclusions can’t be detected using only optical microscopy. In the cast iron with 14.7% Cu, distribution of inclusions has two peaks: 30 ... 40 ... 150 microns and 160 microns. Out-of-shape cupric inclusions of the size of ~ 1 micron are detected in the ledeburite cementite.Submicron inclusions are observed in the lamellar pearlite colonies. With increase of copper content up to ~ 7 wt. % cast iron hardness and microhardness of pearlite increases.

Influence of modifying with silicocalcium (SiCa) on the structure and friction properties of the hypereutectoid steel alloyed with 8.85 wt. % of Cu was studied. SiCa modifying of the copper alloyed hypereutectoid steel, led to the formation of the vermicular graphite distributed in the indendritic space instead of cementite. Coefficient of friction reduction and increased wear resistance were marked in the copper alloyed hypereutectoid steel due to the presence of graphite and cupric inclusions in the steel structure. The wear resistance of the graphitized hypereutectoid steel alloyed with 8.85 wt. % of Cu was almost 5 times higher compared to the wear resistance of bronze BrA9J3L and 75% higher compared to the wear resistance of antifriction cast iron AChS-1.