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Brown, Jason I. (author), Kolokolnikov, Theodore (author), Kooij, Robert (author)We introduce two new methods for approximating the allterminal reliability of undirected graphs. First, we introduce an edge removal process: remove edges at random, one at a time, until the graph becomes disconnected. We show that the expected number of edges thus removed is equal to (Formula presented.), where (Formula presented.) is the...journal article 2024
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Kooij, Robert (author)From the desire to reduce the impact of traveling on the environment and the increase in fuel prices over the past years, the propeller has regained interest as a propulsion mechanism in the aviation industry. Two main reasons can be found in their high propulsive efficiency and ability to combine with electric motors. The scaling of the motors...master thesis 2023
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Wang, F. (author), Kooij, Robert (author)Network controllability and its robustness have been widely studied. However, analytical methods to calculate network controllability with respect to node in and outdegree targeted removals are currently lacking. This paper develops methods, based on generating functions for the in and outdegree distributions, to approximate the minimum...journal article 2023
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Wang, F. (author), Cetinay, Hale (author), He, Zhidong (author), Liu, L. (author), Van Mieghem, P.F.A. (author), Kooij, Robert (author)For this study, we investigated efficient strategies for the recovery of individual links in power grids governed by the direct current (DC) power flow model, under random link failures. Our primary objective was to explore the efficacy of recovering failed links based solely on topological network metrics. In total, we considered 13 recovery...journal article 2023
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Wang, F. (author), Kooij, Robert (author)Network controllability is a critical attribute of dynamic networked systems. Investigating methods to restore network controllability after network degradation is crucial for enhancing system resilience. In this study, we develop an analytical method based on degree distributions to estimate the minimum fraction of required driver nodes for...journal article 2023
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Xu, Ran (author), Wang, F. (author), Kooij, Robert (author)In this paper we investigate the controller placement problem on networks using controller reachability as the network performance metric. This metric is defined as the probability that each node can reach at least one controller, given that each link is operational with a fixed probability. By exploring placements for more than 100 realworld...conference paper 2023
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Kooij, Robert (author), Zegeling, André (author)We present a mechanical model for an oscillator with one degree of freedom under the influence of a flowing medium. Under fairly general conditions we show that the ensuing differential equation has at most two limit cycles and we give examples where exactly two limit cycles will occur. The implications of this result are that it is possible...journal article 2023
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Kooij, Robert (author), Achterberg, M.A. (author)The effective graph resistance, also known as the Kirchhoff index, is metric that is used to quantify the robustness of a network. We show that the optimisation problem of minimizing the effective graph resistance of a graph by adding a fixed number of links, is NPhard.journal article 2023
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Predari, Maria (author), Berner, Lukas (author), Kooij, Robert (author), Meyerhenke, Henning (author)The total effective resistance, also called the Kirchhoff index, provides a robustness measure for a graph G. We consider two optimization problems of adding k new edges to G such that the resulting graph has minimal total effective resistance (i.e., is most robust)—one where the new edges can be anywhere in the graph and one where the new...journal article 2023
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Wezeman, Robert S. (author), Neumann, N.M.P. (author), Phillipson, F. (author), Kooij, Robert (author)In this paper we study encounterbased density estimation using different random walks and analyse the effects of the stepsize on the convergence of the density approximation. Furthermore, we analyse different types of random walks, namely, a uniform random walk, with every position equally likely to be visited next, a classical random walk...conference paper 2023
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Wang, F. (author), Kooij, Robert (author)Network controllability and its robustness has been widely studied. However, analytical methods to calculate network controllability with respect to node removals are currently lacking. This paper develops methods, based upon generating functions for the in and outdegree distributions, to approximate the minimum number of driver nodes...conference paper 2023
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Liu, X. (author), Achterberg, M.A. (author), Kooij, Robert (author)pinion dynamics models study how the interaction among people influences the opinion formation process. In most opinion dynamics models, only one opinion can exist in the steady state, which is different from the reallife opinion formation process. In 2009, Shao et at. introduced a NonConsensus Opinion (NCO) model, which allows different...conference paper 2022
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Horsevad, Nikolaj (author), Mateo, David (author), Kooij, Robert (author), Barrat, Alain (author), Bouffanais, Roland (author)The original version of this Article contained an error in the Abstract, which incorrectly read: ‘Here, we show theoretically, and experimentally with a multirobot system, that such a transition from simple to complex contagion can also bed observed in an archetypal model of distributed decisionmaking devoid of any thresholds or...journal article 2022
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Horsevad, Nikolaj (author), Mateo, David (author), Kooij, Robert (author), Barrat, Alain (author), Bouffanais, Roland (author)How does the spread of behavior affect consensusbased collective decisionmaking among animals, humans or swarming robots? In prior research, such propagation of behavior on social networks has been found to exhibit a transition from simple contagion—i.e, based on pairwise interactions—to a complex one—i.e., involving social influence and...journal article 2022
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Kumaresan, Anusha (author), Kandasamy, Nandha Kumar (author), Kooij, Robert (author)The endeavour towards making power distribution systems (PDSs) smarter has made the interdependence on communication network indispensable. Further, prospective high penetration of intermittent renewable energy sources in the form of distributed energy resources (DERs) has resulted in the necessity for smart controllers on such DERs....journal article 2022
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Chen, Anqi (author), Sun, P. (author), Kooij, Robert (author)Network recoverability refers to the ability of a network to recover to a desired performance level after suffering topological perturbations such as link failures. The minimum number of driver nodes is a typical metric to denote the network controllability. In this paper, we propose closedform analytic approximations for the minimum number of...conference paper 2021
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Dhiman, Ashish (author), Sun, P. (author), Kooij, Robert (author)This paper presents machine learning based approximations for the minimum number of driver nodes needed for structural controllability of networks under linkbased random and targeted attacks. We compare our approximations with existing analytical approximations and show that our machine learning based approximations significantly outperform...conference paper 2021
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Sun, P. (author), He, Z. (author), Kooij, Robert (author), Van Mieghem, P.F.A. (author)Optical networks are vulnerable to failures due to targeted attacks or largescale disasters. The recoverability of optical networks refers to the ability of an optical network to return to a desired performance level after suffering topological perturbations such as link failures. This paper proposes a general topological approach and...journal article 2021
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Zegeling, André (author), Kooij, Robert (author)The research presented in this paper compares the occurrence of limit cycles under different bifurcation mechanisms in a simple system of twodimensional autonomous predator–prey ODEs. Surprisingly two unconventional approaches, for a singular system and for a system with a center, turn out to produce more limit cycles than the traditional...journal article 2021
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Sun, P. (author), Kooij, Robert (author), Van Mieghem, P.F.A. (author)In this paper, we propose closedform analytic approximations for the number of controllable nodes in sparse communication networks from the aspect of network controllability, considering linkbased random attack, targeted attack, as well as random attack under the protection of critical links. We compare our approximations with simulation...journal article 2021