Informational entropy : a failure tolerance and reliability surrogate for water distribution networks

Evolutionary algorithms are used widely in optimization studies on water distribution networks. The optimization algorithms use simulation models that analyse the networks under various operating conditions. The solution process typically involves cost minimization along with reliability constraints that ensure reasonably satisfactory performance under abnormal operating conditions also. Flow entropy has been employed previously as a surrogate reliability measure. While a body of work exists for a single operating condition under steady state conditions, the effectiveness of flow entropy for systems with multiple operating conditions has received very little attention. This paper describes a multi-objective genetic algorithm that maximizes the flow entropy under multiple operating conditions for any given network. The new methodology proposed is consistent with the maximum entropy formalism that requires active consideration of all the relevant information. Furthermore, an alternative but equivalent flow entropy model that emphasizes the relative uniformity of the nodal demands is described. The flow entropy of water distribution networks under multiple operating conditions is discussed with reference to the joint entropy of multiple probability spaces, which provides the theoretical foundation for the optimization methodology proposed. Besides the rationale, results are included that show that the most robust or failure-tolerant solutions are achieved by maximizing the sum of the entropies

Editorial introduction

Tiku Tanyimboh, Senior Lecturer in Civil Engineering at the University of Strathclyde provides this editorial to water management

Seamless pressure-deficient water distribution system model

Pressure-deficient conditions are a common occurrence in water distribution systems. These situations require accurate modelling for timely decision making. However, the conventional demand-driven analysis approach to network modelling is unsuitable for operating conditions with insufficient pressure. Increasing emphasis is being placed on the need for water companies to satisfy stringent performance standards for the continuous supply of water to consumers and it is those pressure-deficient operating conditions which are critical in determining whether or not adequate supplies can be provided. It is therefore very unfortunate that the demand-driven analysis method becomes invalid for use in precisely those critical conditions. The aim of this paper is to present a new pressure-dependent demand function to help improve the simulation of pressure-deficient conditions. The proposed function has better computational properties than those in the literature and has been incorporated successfully in the governing equations for water distribution networks. In particular, the proposed function and its derivative do not have the discontinuities that often cause convergence difficulties in the solution of the constitutive equations. A robust Newton–Raphson algorithm was developed to model water distribution systems under both normal and pressure-deficient conditions in a seamless way. Examples which demonstrate the methodology are included

"Adaptive response" - some underlying mechanisms and open questions

Organisms are affected by different DNA damaging agents naturally present in the environment or released as a result of human activity. Many defense mechanisms have evolved in organisms to minimize genotoxic damage. One of them is induced radioresistance or adaptive response. The adaptive response could be considered as a nonspecific phenomenon in which exposure to minimal stress could result in increased resistance to higher levels of the same or to other types of stress some hours later. A better understanding of the molecular mechanism underlying the adaptive response may lead to an improvement of cancer treatment, risk assessment and risk management strategies, radiation protection, e. g. of astronauts during long-term space flights. In this mini-review we discuss some open questions and the probable underlying mechanisms involved in adaptive response: the transcription of many genes and the activation of numerous signaling pathways that trigger cell defenses - DNA repair systems, induction of proteins synthesis, enhanced detoxification of free radicals and antioxidant production.Publisher PDFPeer reviewe