1,721,092 research outputs found
Models and algorithms for the pollution-routing problem and its variations
No full textThis thesis is positioned within the field of green logistics with respect to CO2 emissions in road freight transportation. In order to examine the different aspects of CO2 emissions of freight transportation, three related, but different research questions are studied. Because CO2 emissions are proportional to the amount of the fuel consumed by vehicles, the first goal of the thesis is to review and compare several available fuel emission models. The results of extensive computational experiments show that all emission models tested are sensitive to changes in load, speed and acceleration. Second, the dissertation studies the Pollution-Routing Problem (PRP), an extension of the classical Vehicle Routing Problem with Time Windows (VRPTW). The PRP consists of routing a number of vehicles to serve a set of customers within preset time windows, and determining their speed on each route segment, so as to minimise a function comprising fuel, emission and driver costs. A mathematical formulation of this problem cannot be solved to optimality for medium to large scale instances. For this reason, the thesis describes an adaptive large neighbourhood search (ALNS) based algorithm to solve the PRP. The algorithm iterates between a VRPTW and a speed optimisation problem, where the former is solved through an enhanced ALNS and the latter is solved using a polynomial time speed optimisation algorithm (SOA). The third question relates to the PRP and the two important objectives that should be taken into account, namely minimisation of fuel consumption and total driving time. Computational results on a large set of PRP instances show that the algorithm is both effective and efficient in solving instances of up to 200 nodes. The thesis therefore studies the bi-objective PRP where one of the objectives is related to the environment, namely fuel consumption (hence CO2 emissions), and the other to driving time. An enhanced ALNS algorithm is described to solve the bi-objective PRP. The algorithm integrates the classical ALNS scheme with a specialized SOA. The results show that one need not compromise greatly in terms of driving time in order to achieve a significant reduction in fuel consumption and CO2 emissions
The pollution-routing problem with speed optimization and uneven topography
No full textThis paper considers a joint pollution-routing and speed optimization problem (PRP-SO) where fuel costs and emissions depend on the vehicle speed, arc payloads, and road grades. We present two methods, one approximate and one exact, for solving the PRP-SO. The approximate strategy solves large-scale instances of the problem with a tabu search-based metaheuristic coupled with an efficient fixed-sequence speed optimization algorithm. The second strategy consists of a tailored branch-and-price (BP) algorithm in which speed optimization is managed within the pricing problem. We test both methods on modified Solomon benchmarks and newly constructed real-life instance sets. Our BP algorithm solves most instances with up to 50 customers and many instances with 75 and 100 customers. The heuristic is able to find near-optimal solutions to all instances and requires less than one minute of computational time per instance. Results on real-world instances suggest several managerial insights. First, fuel savings of up to 53\% are realized when explicitly taking into account arc payloads and road grades. Second, fuel savings and emissions reduction are also achieved by scheduling uphill customers later along the routes. Lastly, we show that ignoring elevation information when planning routes leads to highly inaccurate fuel consumption estimates
A metaheuristic approach for the multi-objective sustainable vehicle routing problem
No full textThis study introduces the Multi-Objective Sustainable Vehicle Routing Problem (MOSVRP) with time windows, designed for congested urban networks. The model simultaneously addresses economic, environmental, and social sustainability by minimizing costs and emissions while maximizing customer satisfaction through enhanced service at pickup nodes. To manage the complexity of large-scale urban routing, we propose a novel Voronoi diagram-based network shrinking procedure that significantly reduces computational effort. More specifically, the model incorporates time-dependent traffic patterns to capture realistic urban conditions. For the solution, we propose a tailored metaheuristic, the enhanced Multi-Objective Volleyball Premier League algorithm (MOVPL), which incorporates reference point guidance, disruption operators, and adaptive weight adjustment. This hybrid approach effectively balances conflicting objectives and improves solution diversity. Applied to Tehran’s urban freight network, the proposed method demonstrates superior performance across all metrics compared to benchmark algorithms and exact methods. Results show notable reductions in fuel consumption and travel distance, alongside improved service equity. Furthermore, the framework offers a scalable and transferable solution for sustainable logistics in other urban contexts
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A selected review on the negative externalities of the freight transportation: modeling and pricing
Full text linkThe planning of freight transportation activities creates benefits as well as costs. Among those costs, some of them, namely externalities, fall on other people/society that have no direct relevance to the operations of transportation. Such externalities are accrued expenses which should be addressed by actual pricing policies to enable an efficient and sustainable freight transportation system. This paper reviews externalities in quantitative terms, and then provides pricing studies of these costs per unit of freight transported along with the most recent estimations. The associated negative externalities are structured by transportation mode (road, rail, maritime, and air)
The pollution-routing problem with speed optimization and uneven topography
Full text linkThis paper considers a joint pollution-routing with time windows and speed optimization problem (PRP-SO) where vehicle speed, payload, and road grade influence fuel costs and CO2e emissions. We present two advanced optimization methods (i.e., approximate and exact) for solving the PRPSO. The approximate strategy solves large- scale instances of the problem with a Tabu search-based metaheuristic coupled with an efficient fixed-sequence speed optimization algorithm. The second strategy consists of a tailored branch-and-price (BP) algorithm to manage speed optimization within the pricing problem. We test both methods on modified Solomon benchmarks and newly constructed real-life instance sets. Our BP algorithm successfully solves the majority of instances involving up to 50 customers and many instances with 75 and 100 customers. The heuristic can find near-optimal solutions to all instances and requires less than one minute of computational time per instance. Results on real-world instances suggest several managerial insights. First, fuel savings of up to 53% can be achieved when explicitly considering arc payloads and road grades. Second, fuel savings and emission reduction can be achieved by scheduling uphill customers later along the routes. Lastly, we show that ignoring elevation information when planning routes leads to highly inaccurate fuel consumption estimates
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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