1,720,995 research outputs found
An effective mitigation strategy to hedge against absenteeism of occasional drivers
Full text linkCompanies can use occasional drivers to increase efficiency on last-mile deliveries. However, as occasional drivers are freelancers without contracts, they can decide at short notice whether they perform delivery requests. If they do not perform their tasks, this is known as driver absenteeism, which obviously disrupts the operations of companies. This paper tackles this problem by developing an auction-based system, including a mitigation strategy to hedge against the absenteeism of occasional drivers. According to this strategy, a driver can bid not only for serving bundles but also to act as a reserved driver. Reserved drivers receive a fee to ensure their presence but are not guaranteed to be assigned to a specific bundle. The problem is modeled as a two-stage stochastic problem with recourse activation. To solve this problem, this paper develops a self-learning matheuristic (SLM) and an iterated local search (ILS) that exploits SLM as a local search operator. Through an extensive computational study, this paper shows the clear dominance of the newly proposed approach in terms of solution quality, run times, and customers’ perceived quality of service compared against three different deterministic approaches. The Value of the Stochastic Solution, a well-known stochastic parameter, is also analyzed. Finally, the identikit of the perfect reserved driver, based on data observed in optimal solutions, is discussed
Location Techniques for the Design of a Walking Aid Network for Visual Impaired Students
No full textUsing combinatorial auctions for the procurement of occasional drivers in the freight transportation: A case-study
No full textThe logistics companies should continuously invent novel solutions to oppose fierce competition. Introducing occasional drivers in the context of freight transportation can represent a valuable option. This paper is concerned with reinforcing the distribution capability of a real-life company by using the novel paradigm of crowdshipping, besides employing its fleet of vehicles. Crowdshipping consists involving occasional drivers, which are to be selected from the public through the use of the combinatorial auction paradigm. We propose a mathematical model that integrates the decisions related to the vehicle routing with the winner determination problem for the occasional drivers’ selection. The objective is to minimize the overall transportation cost of using the company's available fleet plus the cost of employing external drivers. We also propose two heuristic methods to solve real-life distribution instances; one is based on the decomposition method and the other on a cost-comparison greedy approach. The validity of the model, as well as the heuristic methods, has been verified by solving a real case study related to an online bookstore with door-to-door delivery in Oman. Our computational results show savings that reach 30 with respect to the solution implemented by the company. © 2021 Elsevier Lt
Solving the Flood Propagation Problem with Newton Algorithm on Parallel Systems
Full text linkIn this paper we propose a parallel implementation for the flood propagation method Flo2DH. The model is built on a finite element spatial approximation combined with a Newton algorithm that uses a direct LU linear solver. The parallel implementation has been developed by using the standard MPI protocol and has been tested on a set of real world problems
Solving the Periodic Edge Routing Problem in the Municipal Waste Collection
No full text In many municipal waste collection systems, it is necessary to extend the planning horizon to more than one working day. This can happen, for example, in the collection of some recyclable articles. In this case, some of the streets must be served every day but others need only once every two days service. In this paper, we focus on planning the routing of the collection vehicles while extending the planning horizon to two working days. We propose a simple, but effective, heuristic approach and we carry out extensive computational experiments to evaluate its performance. We also apply our method to solve a real-case application related to the collection of recyclable wastes in a small Italian city. </jats:p
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
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