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Determining contingency aware dispatch decisions by solving a security-constrained optimal power flow (SCOPF) is challenging for real-world power systems, as the high problem dimensionality often leads to impractical computational requirements. This problem becomes more severe when the SCOPF has to be solved not only for a single instance, but for multiple periods, e.g. in the context of electricity market analyses. This paper proposes an algorithm that identifies the minimal set of constraints that exactly define the space of feasible nodal injections for a given network and contingency scenarios. By internalizing the technical limits of the nodal injections and enforcing a minimal worst-case impact of contingencies to line flows, computational effort can be further improved. The case study applies and analyzes the methods on the IEEE 118 and A&M 2000 bus systems, as well as the German and European transmission systems. In all tested cases the proposed algorithm identifies at least 95% of the network and security constraints as redundant, leading to significant SCOPF solve time reductions. Scalability and practical implementation are explicitly discussed. The code and input data of the case study is published supplementary to the paper under an open-source license. [ABSTRACT FROM AUTHOR]

This paper describes the algorithms used in a planning and scheduling software tool developed for the European Space Agency in the framework of the Mars Express mission. The planning and scheduling algorithm computes a feasible schedule for the transmission of telecommands (TCs) from the ground segment to the space segment, complying with a number of technical constraints. Owing to the distance between Mars and Earth, it is important that the robustness of the schedule is taken into account because repair operations may be very time consuming or even impossible. For this reason, besides the maximization of the number of TCs transmitted from Earth to Mars, the scheduler is also designed to maximize the number of full confirmations and secondary time windows, which are two special characteristics of the Mars Express schedule explicitly designed for the sake of robustness. Besides the maximization of robustness, the scheduling algorithm that can run with different settings can be used to optimize some secondary figures of merit, such as the average saturation of the memory devices of the space segment and the usage of the time windows available for communication. Computational results on real instances are presented. [ABSTRACT FROM PUBLISHER]

Abstract: This paper addresses a hub-and-spoke network problem for railroad freight, where a central planner is to find transport routes, frequency of service, length of trains to be used, and transportation volume. Hub-and-spoke networks, often found in air freight, have not been favoured by railways in the past. Such a structure could be profitable, however, if there exist concentrated freight flows on some service links. We formulate a linear integer programming model whose objective function includes not only the typical operational cost, but also cost due to the transit time spent by freight in the network. We then develop heuristic algorithms to solve large scale instances occurring in rail freight systems in France plus Italy; Germany; and a 10-country European network. By assuming that every node is equipped with consolidation capability, we let the final solution naturally reveal potential hub locations, the impact of several of which is studied by sensitivity analysis. [Copyright &y& Elsevier]

Assessing the performance of transit systems operating under different regulatory regimes is a topic of considerable interest in the literature. The goal of this paper is to investigate the performance characteristics and factors affecting this performance for European transit systems operating in vastly different regulatory environments. The initial results of data envelopment analysis application indicate that privately operated systems tend to be more efficient while publicly operated systems tend to be more effective; transport operators in cities where open entry form of competition has been introduced were found to perform both efficiently and effectively. Further, as the Tobit regressions focused on the effect of ownership indicate, most systems in the sample demonstrate a positive trend in both efficiency and effectiveness, a finding with important practical implications for financially strained systems. [ABSTRACT FROM AUTHOR]