Effectiveness retention ratio and its standardization

Aim. To promote a better understanding, a wider and more correct application of the effectiveness retention ratio. That is the measure that is best suited for assessing the dependability of complex technical systems, in which partial failures are possible that put a system into intermediate states between complete up and down ones. Methods. The paper uses the methods of the probability theory and comparative analysis of texts of interstate (Euro-Asian), Russian and international dependability-related standards. Results. The principal contribution of Russian researchers to the creation and development of methods for applying effectiveness indicators to estimating the dependability of complex systems is pointed out. Shortcomings were identified in the basic dependability-related standards as regards the effectiveness retention ratio and related concepts. Namely, in terminology standard GOST 27.002–2015, the phrases that require improvement are indicated. They relate to the concepts of partial failure, partial up state and partial down state. A broader and more ac[1]curate definition of partial failure is suggested. It is noted that the relationship between partially up and partially down states are to be discussed and clarified. GOST 27.003–2016 that establishes the content and general rules for specifying dependability requirements contains wording errors in the classification of items according to the number of possible (taken into consideration) states and in the examples of possible variants of the effectiveness retention ratio in various branches of technology that are probabilities of task completion, etc. The paper suggests corrections to the appropriate wordings. It has been established that although the effectiveness retention ratio is not referred to in the international dependability-related terminology standard (IEC 60050-192:2015), it implicitly appears in two IEC standards (IEC 61703:2016 and IEC 62673:2013), in which it is assigned to availability measures. Conclusion. The paper’s findings will be useful to experts involved in the assessment and standardization of complex technical system dependability. Their implementation will help improve interstate, Russian and international dependability-related standards.

Stochastic Analysis of a Priority Standby System under Preventive Maintenance

In this paper, we propose a system of two dissimilar units: one unit prioritizes operation (priority unit), and the other unit is kept as a cold standby (ordinary unit). In this system, we assume that the failures, repairs, and preventive maintenance (PM) times follow arbitrary distributions for both units, except for the fact that the repair time of the ordinary unit follows an exponential distribution. The priority unit has normal, partial failure or total failure modes, while the ordinary unit has normal or total failure modes. The PM of the system can be started after time t when (i) the priority unit is in the normal or partial failure modes up to time t and (ii) the standby unit is available up to time t. PM can be achieved in two types: the costlier type with probability p and the cheaper type with probability (1−p). Under these assumptions, we investigate the reliability measures of the system using the regenerative point technique. Finally, we show a numerical example to illustrate the theoretical findings and show the effect of preventive maintenance in the reliability measures of the proposed system.

8. Resulting Trusts

This chapter examines the nature of the resulting trust. It explains that a trust is called resulting when the beneficial interest in the property returns to the person who transferred the property in the first place. It discusses the theoretical foundation of the resulting trust and its categories, which include presumed and automatic resulting trusts. This chapter examines the consequences of a total or partial failure of express trust and the Quistclose trust which arises where property is transferred for a purpose which has failed, and suggests that there is no need to expand the resulting trust to encompass claims in unjust enrichment and following the rescission of a contract.

Spinal stabilisation using a polyvinilidine (Lubra) plate in a pot-bellied pig

A three-month-old pot-bellied pig presented for acute paraplegia following a presumptive fall. CT examination identified a vertebral subluxation of L1–L2 with a comminuted fracture of the L1 vertebra. Spinal stabilisation was performed with polyvinilidine (Lubra) plates. The pig improved neurologically and regained the ability to walk. Spinal radiographs six weeks following surgery revealed partial failure of the plates in the caudal aspect of the vertebral column and suspected pressure atrophy of spinous processes. Eighteen months later, the plates were piercing through the skin, so they were removed surgically and the pig did well from then on. This case report describes the feasibility of spinal stabilisation in a pot-bellied pig associated with a good outcome, but also reveals potential complications and spinal changes that can be observed after use of polyvinilidine plates in this species.