Forgetting complex propositions

This paper uses possible-world semantics to model the changes that may occur in an agent's knowledge as she loses information. This builds on previous work in which the agent may forget the truth-value of an atomic proposition, to a more general case where she may forget the truth-value of a propositional formula. The generalization poses some challenges, since in order to forget whether a complex proposition $\pi$ is the case, the agent must also lose information about the propositional atoms that appear in it, and there is no unambiguous way to go about this. We resolve this situation by considering expressions of the form $[\boldsymbol{\ddagger} \pi]\varphi$, which quantify over all possible (but minimal) ways of forgetting whether $\pi$. Propositional atoms are modified non-deterministically, although uniformly, in all possible worlds. We then represent this within action model logic in order to give a sound and complete axiomatization for a logic with knowledge and forgetting. Finally, some variants are discussed, such as when an agent forgets $\pi$ (rather than forgets whether $\pi$) and when the modification of atomic facts is done non-uniformly throughout the model

Wireless Backhaul Networks: Minimizing Energy Consumption by Power-Efficient Radio Links Configuration

In this work, we investigate on minimizing the energy consumption of a wireless backhaul communication network through a joint optimization of data routing and radio configuration. The backhaul network is modeled by a digraph in which the nodes represent radio base stations and the arcs denote radio links. According to the scenario under consideration, a power-efficient configuration can be characterized by a modulation constellation size and a transmission power level. Every link holds a set of power-efficient configurations, each of them associating a capacity with its energy cost. The optimization problem involves deciding the network's configuration and flows that minimize the total energy expenditure, while handling all the traffic requirements simultaneously. An exact mathematical formulation of the problem is presented. It relies on a minimum cost multicommodity flow with step increasing cost functions, which is very hard to optimize. We then propose a piecewise linear convex function, obtained by linear interpolation of power-efficient configuration points, that provides a good approximation of the energy consumption on the links, and present a relaxation of the previous formulation that exploits the convexity of the energy cost functions. This yields lower bounds on the energy consumption, and finally a heuristic algorithm based on the fractional optimum is employed to produce feasible solutions. Our models are validated through extensive experiments that are reported and discussed. The results verify the potentialities behind this novel approach. In particular, our algorithm induces a satisfactory integrality gap in practice

Viability of bridge inspectors determining defect ratings using photographic images

The visual inspection of bridges is a major undertaking for asset owners and operators. In the UK, visual inspections require inspectors to visit bridges on site and often at night and under unfavourable weather conditions. Therefore, it would be beneficial to move some of the visual inspection process off site. This paper studies whether the defect classification aspects of the inspection process could be conducted remotely using photographs. This study examines the defect ratings assigned by ten survey participants who were tasked with examining photographs from visual inspections of ten UK bridges. The survey results were compared with the results from the general inspections previously carried out for the bridges in question. From this data set, the differences in the ratings given and the extent to which defects are missed were examined. The results show that a higher number of defects were identified for a given bridge by the remote inspectors. Statistical analysis shows that aggregated defects rated by off-site inspectors tend to be more severe and of a higher priority rating compared with those from the on-site inspectors. The results also indicate that there is closer agreement between on-site and off-site inspectors for defects of a higher severity rating.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Hydraulic Structures and Flood Ris

Tradeoffs in routing reconfiguration problems

International audienceNous étudions le problème du reroutage d'un ensemble de connexion dans un réseau. Il consiste à passer d'un routage initial (ensemble de chemins reliant des paires de noeuds) à un autre, en traitant séquentiellement chaque connexion. Il est parfois indispensable d'en interrompre temporairement certaines au cours du processus de reconfiguration, ce qui nous amène à étudier les compromis possibles entre deux mesures d'efficacité : le nombre total de connexions interrompues et le nombre maximum de connexions interrompues simultanément. Nous prouvons qu'établir de tels compromis mène à des problèmes NP-complets et difficiles à approcher (APX-difficiles voir non APX). Nous montrons ensuite que de bons compromis sont impossibles en général. Enfin, nous exhibons une classe d'instances de reroutage pour laquelle il est possible de minimiser le nombre de requêtes interrompues simultanément sans "trop" augmenter le nombre total de connexions interrompues. Ces résultats sont obtenus en modélisant ce problème par un jeu à l'aide d'agents mobiles

Minimizing Energy Consumption by Power-Efficient Radio Configuration in Fixed Broadband Wireless Networks

International audienceIn this paper, we investigate on minimizing the energy consumption of a fixed broadband wireless network through a joint optimization of data routing and radio configuration. The network is modeled by a digraph in which the nodes represent radio base stations and the arcs denote radio links. Under this scenario, a power-efficient configuration can be characterized by a modulation constellation size and a transmission power level. Every link holds a set of power-efficient configurations, each of them associating a capacity with its energy cost. The optimization problem involves deciding the network's configuration and flows that minimize the total energy consumption, while handling all the traffic requirements simultaneously. An exact mathematical formulation of the problem is presented. It relies on a minimum cost multicommodity flow with step increasing cost functions, which is very hard to optimize. We then propose a piecewise linear convex function, obtained by linear interpolation of powerefficient configuration points, that provides a good approximation of the energy consumption on the links, and present a relaxation of the previous formulation that exploits the convexity of the energy cost functions. This yields lower bounds on the energy consumption, and finally a heuristic algorithm based on the fractional optimum is employed to produce feasible solutions. Our models are validated through extensive experiments that are reported and discussed. The results verify the potentialities behind this novel approach. In particular, our algorithm induces a satisfactory integrality gap in practice

Joint Optimization of Routing and Radio Configuration in Fixed Wireless Networks

International audienceNous étudions la minimisation de la consommation d'énergie des réseaux sans-fil fixes à transmission par liens microondes, par l'optimisation jointe du routage des flux de données et la sélection de la configuration des liens. Nous présentons une formulation mathématique exacte basée sur un multiflot entier de coût minimum avec des fonctions de coût en escalier, rendant le problème très difficile à résoudre. Nous proposons ensuite une fonction linéaire par morceaux convexe, obtenue par interpolation linéaire des points de configuration efficaces en énergie, qui fournit une bonne approximation de la consommation d'énergie sur les liens, et présentons une relaxation qui exploite la convexité des fonctions de coût. Ceci rapporte des limites inférieures sur la consommation d'énergie, et finalement un algorithme heuristique basé sur l'optimum fractionnaire est utilisé pour produire des solutions réalisables. Les résultats attestent du potentiel de notre nouvelle approche