Dynamic contact problems with unilateral limitations for elastic bodies with cracks

The hydrogasodynamics and technology a of melt treatment out of furnace by high-implused jets of neutral gas were studied. The conception of a jet synthesis, blowing regimes and devices to solve problems of melt treatment in ladle was developed. The appropriatenesses of melt degassing and homogenizig in ladle at the blowing by trans- and ultrasonic jets of neutral gas were obtained experimentaly. The approptiatenesses of gas-powder jets outflow were studied and a new class of blowing regimes and devices for powder material injection was developed. The principles of construction and optimization of regime parameters of blowing devices, regimes and devices for melt degassing by trans- and ultrasonic jets of neutral gas to inject the powder materials in a melt, technological decisions, concerning the correction of the chemical composition and temperature of a melt in ladle were developed. The principles of a temperature melting regime optimization were developed. The results obtained were applied in the West-Siberian Metallurgical works. The increase of the metal quality allowed to decrease the reject by 20-30%. The yield of steel was increased by 0,1-0,3%, the steel temperature on tap was decreased by 10-25% the specific expense of cast iron was decreased by 2-4 kg/t, the ferroalloy expense was reduced by 3-8%. The results may be use in steelmakingAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

An infinite-server queue influenced by a semi-Markovian environment

We consider an infinite-server queue, where the arrival and service rates are both governed by a semi-Markov process that is independent of all other aspects of the queue. In particular, we derive a system of equations that are satisfied by various "parts" of the generating function of the steady-state queue-length, while assuming that all arrivals bring an amount of work to the system that is either Erlang or hyperexponentially distributed. These equations are then used to show how to derive all moments of the steady-state queue-length. We then conclude by showing how these results can be slightly extended, and used, along with a transient version of Little’s law, to generate rigorous approximations of the steady-state queue-length in the case that the amount of work brought by a given arrival is of an arbitrary distribution

UM MODELO MARKOVIANO DE DECISÃO PARA A OTIMIZAÇÃO DE UM SISTEMA DE MANUTENÇÃO COM TEMPOS DE REPARO COXIANOS E FASES NÃO OBSERVÁVEIS

Neste artigo analisa-se um sistema de manutenção de máquinas com dois servidores diferentes, tempos até a quebra das máquinas exponencialmente distribuídos e tempos de reparo seguindo uma distribuição do tipo fase com configuração de Cox. Consideram-se dois modelos que se diferenciam pela possibilidade ou não de se observar as fases das distribuições do tipo fase: um modelo com informação completa e um modelo com informação parcial. No primeiro caso, modela-se o sistema por um processo markoviano de decisão a tempo contínuo e no segundo por um processo markoviano de decisão com informação parcial, conforme este é definido em Hordijk & Loeve (1994). Resultados numéricos são apresentados<br>In this paper we analyse a manufacturing system with two different servers. The times to failure follow an exponential distribution and the machines repair times follow a phase type distribution with Cox configuration. We consider two models: a full information model and a partial information model, which differ themselves by the possibility of observing or not the phases of the phase type distribution. The first one is modelled by a continuous time Markov decision process, and the second one by a decision Markov processes with partial information, as defined in Hordijk & Loeve (1994). Numerical results are presente