Comparison of two stochastic models for two-unit series system with cold standbys

Reliability characteristics are compared for two stochastic models of a system that has two non-identical units, arranged in series, each unit with its identical cold standby. The same set of assumptions is used for both models, except that in model 2 both of the standby units replace the failed operative unit instantaneously whereas in model 1 an operative failed unit is replaced by its corresponding standby unit (i.e. only one unit is replaced in this case). A single repair facility is available to repair the failed unit. Failure and repair time distributions are assumed to be negative exponential.     

Reliability analysis of a two-unit cold standby redundant system with two operating modes

This paper considers a two unit cold standby redundant system subject to a single repair facility with exponential failure and general repair time distribution. Each unit can work in three different modes — normal, partial failure and total failure. There is a perfect switch to operate the standby unit on total failure of the operative unit. The system has been analysed to determine the reliability parameters e.g. mean time to system failure (MTSF), steady state availability, mean recurrence to a state and expected number of visits to a state, first two moments of time in transient state, by using the theory of Semi-Markov Process. Howard's reward structure has been super-imposed on the Semi-Markov Process to obtained expected profit of the system. A number of results obtained earlier are derived as particular cases.     

Analysis of a two unit standby system with partial failure and two types of repairs

A two dissimiliar unit standby system is analysed. The priority unit can either be in normal or partial operative mode. When the unit fails from the partial mode, it undergoes minor repair and the unit becomes operative with different failure rate. If this unit fails again, it goes to major repair after which it works as good as new. The standby unit while in use is either operative or failed. This non priority unit fails without passing through the partial failure mode and undergoes only one type of repair with different repair time distribution. Failure and repair time distributions are negative exponential and general respectively. Regenerative technique in MRP is applied to obtain several reliability characteristics of interest to system designers.     

Stochastic analysis of a two-unit parallel system with partial and catastrophic failures and preventive maintenance

This paper studies a two-unit parallel system with each unit having two types of failure and two modes of operation—normal or partial failure mode. A unit fails either due to change in operating characteristics or due to catastrophe. The system goes for preventive maintenance randomly (in time). Failure rates are constant while repair and (preventive) maintenance rates are general. Using the theory of regenerative and Markov-renewal processes several important measures of reliability are obtained.     

Stochastic behaviour of a two-unit standby system with better utilization of units

This paper obtains various measures of reliability of a two-unit redundant system with three modes. Upon partial failure of an operative unit the cold standby starts operation only when it becomes active. A single service facility is available (1) for repairing a partially or totally failed unit and (2) to activate the cold standby unit whenever required. Failure time distributions are negative exponential while repair and activating time distributions are general.     

A comprehensive modeling framework for gate stack process dependence of DC and AC NBTI in SiON and HKMG p-MOSFETs

A comprehensive modeling framework involving mutually uncorrelated contribution from interface trap generation and hole trapping in pre-existing, process related gate insulator traps is used to study NBTI degradation in SiON and HKMG p-MOSFETs. The model can predict time evolution of degradation during DC and AC stress, time evolution of recovery after stress, impact of stress and recovery bias and temperature, and impact of several AC stress parameters such as pulse frequency, duty cycle, duration of last pulse cycle (half or full) and pulse low bias. The model can successfully explain experimental data measured using fast and ultra-fast methods in SiON and HKMG devices having different gate insulator processes. The trap generation and trapping sub components of the composite model have been verified by independent experiments. Data published by different groups are reconciled and explained. The model can successfully predict long time DC and AC stress data and has been used to determine device degradation at end of life as EOT is scaled for different HKMG devices.     

Stochastic analysis of a multi-unit cold standby system working in orbit form

This paper considers the analysis of a single server n-similar unit system. Initially k(<n) units form an orbit which functions if one unit functions at a time and the remaining n − k units work as cold standbys. When a unit fails in the orbit it is instantaneously replaced by one of the standbys with the help of a perfect transfer switch. The system is said to fail when n − k + 1 units have failed. The distribution of time to failure and time to repair of a unit are negative exponential. Using the regenerative point technique several reliability characteristics are obtained to carry out the cost-benefit analysis.     

Cost analysis of a two unit priority standby system with imperfect switch and arbitrary distributions

This paper deals with cost analysis of a single server two-unit (one priority and the other ordinary) cold standby system with two modes—normal and total failure. A switch is used to operate the standby unit (ordinary) and it works successfully with known probability p( = 1 ? q). Priority unit gets preference both for operation and repair. Failure and repair time distributions are arbitrary. System fails when switch or both the units fail totally. The system is observed at suitable regenerative epochs in order to obtain reliability characteristics of interest to system designers and operations managers. Explicit results for the exponential time distributions have been obtained in particular cases.     

Stochastic behaviour of man-machine systems operating under different weather conditions

This paper presents two mathematical models to predict the performance of the man—machine systems under different weather conditions. The operator may be in good or poor physical condition which also affects the performance of the system. Failure rate of the system, rate of change of weather conditions as well as rate of change of physical conditions of the operator are assumed to be constant while the repair time distributions are general. Regenerative technique in MRP is applied to obtain several reliability characteristics of interest.     

A two-unit parallel redundant system with three modes and bivariate exponential lifetimes

A two-unit parallel redundant system is applicable in many practical fields, such as computer systems. Whereas the earlier models for such a system have assumed that the failures of the two units are independent, these are taken here to be dependent and have a joint bivariate exponential (BVE) distribution. Each unit has three modes and when the system fails completely, it is repaired (or replaced) with arbitrary rate. Using Sugasaw and Kaji's (Microelectronics and Reliability, 21 (5), 661–670) modification of the regenerative point technique as applied to Markov-renewal process theory, several reliability characteristics of interest to system designers are obtained.