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Abstract In the subway system, passenger crowding in peak hours is likely to cause train delays that easily propagate to following trains, resulting in a lower efficiency of the system. Consequently, this paper focuses on determining a robust timetable for the trains on the one hand, i.e., finding a better timetable to avoid delay propagation as much as possible in case of a crowded subway system. On the other hand, this paper considers the energy efficiency, i.e., reducing the total energy consumption during operations by selecting appropriate speed profiles and maximizing the utilization of regenerative braking energy. A related mathematical optimization model is formulated with the objective of maximizing the robustness and minimizing the total energy consumption. In order to solve this model, an efficient algorithm, i.e., simulation-based variable neighborhood search algorithm, is presented to obtain a good timetable in reasonable amount of time. Finally, experiments are implemented to show the performance of the proposed algorithm.

Abstract The analysis was completed on the main production factors which determine energy characteristics of an electrically-driven hydraulic roller-bit drilling rig during drilling operations under the condition of the Far North deposit. In addition, the correlation ratio between the parameters and electric energy consumption was analyzed for the DM-H drilling rig. The equations expressing the relation of the drilling rig load to the drilling speed have been identified. In order to improve the quality of rock crushing, we have modified the method of determining the properties and condition of the rock mass in order to correct the connection layout of the blasting circuit, the activation system, the change in the type of an explosive agent, as well as the composition and weight of the blasthole charge. The proposed approach allows reducing the cost of drilling and blasting operations by 6 % through the improvement in the accuracy of the designed physical and mechanical properties in terms of both the stratum depth and the strike of the mining block.

The rapid development of metro transit systems brings very significant energy consumption, and the high service frequency of metro trains increases the peak power requirement, which affects the operation of systems. Train scheduling optimization is an effective method to reduce energy consumption and substation peak power by adjusting timetable parameters. This paper proposes a train timetable optimization model to coordinate the operation of trains. The overlap time between accelerating and braking phases is maximized to improve the utilization of regenerative braking energy (RBE). Meanwhile, the overlap time between accelerating phases is minimized to reduce the substation peak power. In addition, the timetable optimization model is rebuilt into a mixed integer linear programming model by introducing logical and auxiliary variables, which can be solved by related solvers effectively. Case studies based on one of Guangzhou Metro Lines indicate that, for all-day operation, the utilization of RBE would likely be improved on the order of 23%, the substation energy consumption would likely be reduced on the order of 14%, and the duration of substation peak power would likely be reduced on the order of 66%.

Fuel efficiency is vital for commercial airlines as fuel is one of the most costly items for airline operations. This study aims to compare fuel efficiencies of selected airlines around the globe and to build a benchmark of fuel efficiency that can be referred to by airlines. By using data on fuel consumption and traffic output collected from various sources including airline annual reports, environmental reports and sustainability reports, this study calculated fuel efficiencies measured by liters of fuel consumed per revenue tonne kilometer (RTK) for the selected airlines in the calendar year 2011 or financial year 2010–2011. Airlines were also compared and ranked by their respective fuel efficiencies. It was found that, depending on whether the passenger equivalent freight mass (PEFM) was 91 kg or 160 kg, the average fuel efficiency of the airlines studied is 0.4 L/RTK or 0.278 L/RTK, respectively. Variances in fuel efficiency among airlines from different regions and airlines of different business models were also found by this study.

Abstract In the daily operation of metro systems, the train scheduling problem aims to find a set of space-time paths for multiple trains that determine their departure and arrival times at metro stations, while train operations are in charge of selecting the best operational speed to satisfy the punctuality and operation costs. Different from the most existing researches that treat these two problems separately, this paper proposes an integrated approach for the train scheduling problem on a bi-direction urban metro line in order to minimize the operational costs (i.e., energy consumption) and passenger waiting time. More specifically, we simultaneously consider (1) the train operational velocity choices that correspond to the energy consumption of trains on each travelling arc, and (2) the dynamic passenger demands at each station for the calculation of total passenger waiting time in the planning horizon. By employing a space-time network representation in the formulations, this complex train scheduling and control problem with dynamic passenger demands is rigorously formulated into two optimization models with linear forms. The first model is an integer programming model that jointly minimizes train traction energy consumption and passenger waiting time. The second model, which is formulated as a mixed-integer programming model, further considers the utilization of regenerative braking energy on the basis of the first model. Due to the computational complexity of these two models, especially for large-scale real-world instances, we develop a Lagrangian relaxation (LR)-based heuristic algorithm that decomposes the primal problem into two sets of subproblems and thus enables to find a good solution in short computational time. Finally, two sets of numerical experiments, involving a relatively small-scale case and a real-world instance based on the operation data of Beijing metro are implemented to verify the effectiveness of the proposed approaches.

The nonresidential solar energy market has grown rapidly in the United States. Companies considering the adoption of solar energy have an important choice: whether to purchase the system (direct ownership, or DO) or opt for an agreement with a service provider that offers third-party ownership (TPO). Although this decision is financially very important, empirical research comparing the two models from an operational perspective has been scarce. These issues are particularly relevant considering that federal and state incentives are commonly used to stimulate adoption. This paper presents an empirical analysis of the role of TPO in the operational performance of nonresidential solar energy installations in California. Using a panel data estimation framework, and accounting for factors that influence TPO adoption, the analysis shows that TPO systems performed, on average, approximately 4% better than DO systems) in terms of their production yield. This performance improvement is consistent with better system design under TPO, but not with better solar panel technology selection by TPO providers.

This article presents a solution that strengthens information security in critical infrastructure entities. Critical infrastructure plays a key role in the functioning of the state and the life of its citizens. Therefore, the protection of critical infrastructure is one of priorities in Poland. The aim of this article is to show that designated postal operators may become an important link in the process of information flow and cybersecurity. Based on their multiple-year experience and expended competences, the operators may provide digital services for entities responsible for the energy security infrastructure. Verification of this goal is necessary, since critical infrastructure is exposed to growing threats, both in the area of energy and other sensitive sectors of the economy. Research results presented in the article were obtained by conducting a CATI survey. The study used the purposeful selection method, which allows to influence the structure of a sample in the context of goals set by the authors. The method solicited key information from experts on postal and energy markets. The results constitute a new approach to the role of the designated postal operator. The authors analysed possibilities to support entities that secure critical infrastructure, including those from the energy sector. It shows that the role of the designated postal operator may significantly change. Taking into account the security of information and cybersecurity, the postal operator could expand its competences, secure infrastructure-related information flow, and thus become a key pillar of the state.

In vertically integrated energy systems, integration frequently entails operational gains that must be traded off against the requisite cost of capacity investments. In the context of the model analyzed in this study, the operational gains are subject to inherent volatility in both the price and the output of the intermediate product transferred within the vertically integrated structure. Our model framework provides necessary and sufficient conditions for the value (NPV) of an integrated system to exceed the sum of two optimized subsystems on their own. We then calibrate the model in Germany and Texas for systems that combine wind energy with Power‐to‐Gas (PtG) facilities that produce hydrogen. Depending on the prices for hydrogen in different market segments, we find that a synergistic investment value emerges in some settings. In the context of Texas, for instance, neither electricity generation from wind power nor hydrogen production from PtG is profitable on its own in the current market environment. Yet, provided both subsystems are sized optimally in relative terms, the attendant operational gains from vertical integration more than compensate for the stand‐alone losses of the two subsystems.