Maximum Repair Time Research Articles

The Importance of Sodium Pyruvate in Assessing Damage Produced by Hydrogen Peroxide

Instability of hydrogen peroxide solutions was noted during the experimental exposure of human cells in culture to hydrogen peroxide in experiments designed to study the production and repair of DNA single-strand breaks. A hydrogen peroxide concentrate was diluted into culture medium, which was then added to experimental cell cultures at various times, with all cultures assessed for DNA damage at 2 h. Only cells treated by the first addition had observable DNA damage. This result was unexpected since these cells had had the maximum repair time. It was determined that the hydrogen peroxide had been eliminated by the culture medium. To determine the mechanism of this elimination, 200 μM hydrogen peroxide was added to various cell culture components, and the solutions were assayed for hydrogen peroxide after 1 h at 37°C. Although most components (except the balanced salts) showed some hydrogen peroxide degradation, it was found that sodium pyruvate was most effective, by a wide margin, in eliminating hydrogen peroxide and its toxic effects. This was confirmed by addition of pyruvate to balanced salt solutions or buffers, and observing the same elimination of hydrogen peroxide. We subsequently found a few earlier reports describing the decarboxylation reaction between hydrogen peroxide and pyruvate, but no kinetic measurements have been published and there seems to be no general appreciation for the very high efficiency of this reaction. The present work presents a preliminary assessment of the importance of pyruvate in the study of hydrogen peroxide and other reactive oxygen species in mammalian cell culture.

Stochastic analysis of a two‐unit cold standby system with maximum repair time and correlated failures and repairs

Investigates a stochastic model of a two identical unit cold standby system. Assumes that, if repair of the failed unit is not completed within a specified time, then an order is placed to replace the failed unit by the new one. The specified time is also known as the maximum repair time limit which may change from user to user of the system, so that it is assumed as a random variable. Joint distribution of failure and repair times is bivariate exponential whereas the distributions of lead time (difference between order and delivery time for a new unit) and replacement time of the new unit are negative exponential. Obtains various reliability characteristics of the system under study by using regenerative point technique. Also studied characteristics through graphs.

Profit analysis of a two multi-component unit standby system with MRT

A stochastic model is investigated for a two-unit (one priority and the other ordinary) cold standby system, when each unit has n independent and non-identical components. It is assumed that the repair of the ordinary unit is completed within a specified time, known as the maximum repair time (MRT); otherwise, the ordinary unit is discarded. The system is observed at suitable regenerative epochs to obtain the profit function. Finally, the behaviour of the profit function is studied graphically in a particular case and values of the parameters are obtained when the profit becomes negative.

A mathematical expression describing the failure probability of a system of redundant components with finite maximum repair time

This paper studies the probability of failure of a system of two or three redundant components. Failure for the system is defined as the failure of all components for the duration of a given finite time T. The implications of this condition of failure duration are discussed. Starting from standard expressions for the probability of failure and the probability of repair with constant failure and repair rates, expressions for the probability of failure as described above are derived. Particular attention is devoted to the part representing the failure to repair, whose derivation is described in detail. Expressions for systems of different components and of identical components are given. Some mathematical properties of the expression for two identical components are discussed and these are related to the properties of the system. Two short examples are given to show the advantages of the application of the new formulae over less accurate expressions.

Reliability of a 2-Unit Standby Redundant System with Constrained Repair Time

This paper considers a 2-unit warm-standby redundant system with repair. The repair of a failed unit is constrained as follows: Associated with each failure of a unit is a random variable termed the Maximum-Repair-Time (MRT) of the failure. If the repair of a failed unit is not completed within the MRT, the unit is rejected for further use. Two types of failure stituations for the system are considered: 1) No allowed down time, and 2) Some allowed down time. Expressions for the Cdf of the Time to System Failure (TSF) and the mean TSF are derived by using Markov renewal processes.

Analysis of Maintenance Man Loading Via Simulation

This paper provides the results of a computer simulation performed to test compliance with a system maintenance requirement. Special attention is given to the selection of the simulation run time (sample size) and fitting a curve to the output data. The actual simulation program was written in the RCA Flow Simulation language which is similar to the IBM GPSS (General-Purpose Simualtion System) language. More specifically, the system requirement was as follows. The probability that the system maintenance-man loading exceeds 4-h repair time in a day (24 h) shall be less than 0.0025. Equipment failures and repairs were simulated via a computer. Equipment failure and repair probability distributions were used as input data. A year's operation was simulated in less than 2-min computer time. A simulation sample size of 360 days was selected on the basis of a statistical analysis using a nonparametric 0.60 confidence level. The results showed a maximum repair time in a day of 130 min, which indicates the system repair time distribution is considerably better than required. The output data were analyzed and the observed repair times were fit with an empirical distribution function.