Friedländer synthesis of poly‐substituted quinolines in the presence of triethylammonium hydrogen sulfate [Et3NH][HSO4] as a highly efficient,and cost effective acidic ionic liquid catalyst

A rapid and an efficient method for the preparation of a variety of substituted quinolines has been developed through the reactions of o‐aminoarylketones with carbonyl compounds containing a reactive α‐methylene moiety in the presence of molten [Et₃NH][HSO₄] under solvent‐free conditions in high yields. J. Heterocyclic Chem., (2011).     

A solvent-free synthesis of 1,2,3,5-tetrasubstituted pyrroles from enaminones and α-haloketones

A simple synthesis of 1,2,3,5-tetrasubstituted pyrrole derivatives from the reaction of enaminone withα-haloketones,under solvent-free conditions,is described.     

Optimal standby activation in m-out-of-n systems: A preventive approach

This article investigates an optimal preventive standby activation policy for an $m$-out-of-$n$ redundant system. We assume that for such a system, which starts operating at time $t=0$, a standby component will be activated at either the failure time of the system or at a predetermined time $\tau$, whichever occurs first. We first obtain the system reliability function under this switching policy as a function of $\tau$. Then, we investigate the optimal switching time $\tau$ so that the mean time to failure of the system is maximized. The results indicate that the existence of an optimal value of $\tau$ depends on the lifetime of the standby redundancy and its virtual age in the standby state. Some illustrative examples are presented to examine the theoretical outcomes.     

An overview of some classical models and discussion of the signature-based models of preventive maintenance

In reliability engineering literature, a large number of research papers on optimal preventive maintenance (PM) of technical systems (networks) have appeared based on preliminary many different approaches. According to the existing literature on PM strategies, the authors have considered two scenarios for the component failures of the system. The first scenario assumes that the components of the system fail due to aging, while the second scenario assumes the system fails according to the fatal shocks arriving at the system from external or internal sources. This article reviews different approaches on the optimal strategies proposed in the literature on the optimal maintenance of multi-component coherent systems. The emphasis of the article is on PM models given in the literature whose optimization criteria (cost function and stationary availability) are developed by using the signature-based (survival signature-based) reliability of the system lifetime. The notions of signature and survival signature, defined for systems consisting of one type or multiple types of components, respectively, are powerful tools assessing the reliability and stochastic properties of coherent systems. After giving an overview of the research works on age-based PM models of one-unit systems and $k$-out-of-$n$ systems, we provide a more detailed review of recent results on the signature-based and survival signature-based PM models of complex systems. In order to illustrate the theoretical results on different proposed PM models, we examine two real examples of coherent systems both numerically and graphically.