1,720,983 research outputs found
The Green Sequencing and Routing Problem
No full textThe paper deals with a sequencing and routing problem originated by a real-world application context. The problem consists in defining the best sequence of locations to visit within a warehouse for the storage and/or retrieval of a given set of items during a specified time horizon, by considering some specific requirements and operating policies which are typical of the kind of warehouse under study. A fleet composed of both electric (i.e., equipped with a lithium-ion battery) and conventional (i.e., with internal combustion engine) forklifts is considered. We model the problem in terms of constrained multicommodity flows on a space-time network, and we extend a matheuristic approach proposed for the case of only conventional vehicles. Preliminary computational results are also presented
Matheuristic approaches to the green sequencing and routing problem
No full textThe paper addresses the green sequencing and routing problem, which consists in determining the best sequence of locations to visit within a warehouse for storing and/or retrieval operations, using a fleet composed of both electric vehicles, e.g., equipped with a lithium-ion battery, and conventional vehicles, i.e., with an internal combustion engine. We present a Mixed-Integer Linear Programming formulation to the problem and propose two matheuristics based on suitable decompositions of the mathematical formulation. The two matheuristics have been tested on a pool of small-medium size instances and their performance has been compared to the one of a third matheuristic, previously proposed for the case of conventional vehicles only and here suitable extended to deal with the green aspects of the problem. The performed analysis allowed one to identify the most promising matheuristic in terms of some standard computational indicators, i.e., computing time and percentage optimality gap, as well as in terms of some qualitative aspects of the solutions agreed with a reference company. Such a most promising algorithm has then been further tested to gather some technical insights on what makes the problem hard to solve, as well as to outline some managerial insights. Moreover, its performance has been tested on a pool of real instances comprising ordinary days (with a usual amount of operations to perform) and extremely busy days, showing its efficacy and efficiency also in the considered real application context
Increasing the reliability of IEEE 802.11ad for industrial applications
No full textWe consider two main aspects related to the application of the IEEE 802.11ad in the industrial environment: the guarantee of a low delivery delay and the reliability of the communication system. Firstly, we discuss the parameter settings of the IEEE802.11ad MAC aimed to guarantee a delivery delay of 1 ms. Then, we formulate a binary linear programming model to enhance the reliability of the system under the Parallel Redundancy Protocol (PRP), while minimizing the number of Access Points (APs) and taking into account the low delivery delay requisite. We propose a heuristic to efficiently solve the design problem, and present the results of a preliminary computational study. The reported results highlight the features of the obtained solutions and give insights on how the proposed heuristic can be used and improved
Design model of an IEEE 802.11ad infrastructure for TSN-based industrial applications
Full text linkThis paper addresses two main aspects related to the application of the IEEE 802.11ad technology in an industrial environment, i.e., to guarantee a low latency and reliable data delivery while reducing the number of the deployed Access Points (APs). First, we discuss the parameter settings of the IEEE802.11ad MAC which guarantee a low delay by exploiting the synchronous service periods (SPs) mechanism. Then, we propose a binary linear programming model to enhance the reliability of the system under the Frame Replication and Elimination for Reliability (FRER). The model minimizes the number of deployed APs by taking into account the constraints on the available synchronous SPs. We also propose two heuristics, based on the described mathematical model, in order to efficiently solve the design problem, then compare the computational performance of the proposed approaches. The reported computational results highlight the complementary features of the compared methods and provide useful guidelines about the usage of the proposed approaches
Robust green Wireless Local Area Networks: A matheuristic approach
Full text linkWe consider the problem of designing a Wireless Local Area Network according to a Green paradigm (GWLAN), i.e. minimizing the power consumption of the network by powering-on just a subset of access points and associating users with the powered-on access points. To protect the system against fluctuations in the data rate transmission between users and access points, which naturally affect the problem because of uncertainty in measuring the exact user position and because of wireless propagation conditions, we address the robust extension of this problem, i.e. the Robust Green Wireless Local Area Networks Problem (RGWLAN), and we propose some robust matheuristics to solve it. Such matheuristics are based on two mathematical models to RGWLAN, i.e. a model based on a generalization of the classical Γ-Robustness framework, and a model exploiting the Multiband Robustness paradigm. The models are enriched by means of a preprocessing powering-on heuristic, aimed at fixing some access points as powered-on, and a reallocation algorithm, aimed at reallocating users to access points once the model solution has been computed, in order to enhance its degree of robustness. The aim is to achieve a good compromise between power saving, guaranteed level of robustness and required computational time. The results of an extensive computational analysis show that the proposed matheuristics solve the RGWLAN in a very efficient way both in terms of power consumption and computational time. Also, they are able to guarantee a high level of robustness with respect to the uncertainty in the user positions. This trend is particularly evident when the users to access points ratio is low, i.e. when the offered traffic to the wireless local area network is scarce, which is the most suitable and relevant scenario for the power consumption optimization
Sequencing and Routing in a Large Warehouse with High Degree of Product Rotation
Full text linkThe paper deals with a sequencing and routing problem originated by a real-world application context.
The problem consists in defining the best sequence of locations to visit within a warehouse for the storage and/or retrieval of a given set of items during a specified time horizon, where the storage/retrieval location of an item is given.
Picking and put away of items are simultaneously addressed, by also considering some specific requirements given by the layout design and operating policies which are typical in the kind of warehouses under study.
Specifically, the considered sequencing policy prescribes that storage locations must be replenished or emptied one at a time by following a specified order of precedence.
Moreover, two fleet of vehicles are used to perform retrieving and storing operations, whose routing is restricted to disjoint areas of the warehouse.
We model the problem as a constrained multicommodity flow problem on a space-time network, and we propose a Mixed-Integer Linear Programming formulation, whose primary goal is to minimize the time traveled by the vehicles during the time horizon.
Since large-size realistic instances are hardly solvable within the time limit commonly imposed in the considered application context, a matheuristic approach based on a time horizon decomposition is proposed.
Finally, we provide an extensive experimental analysis aiming at identifying suitable parameter settings for the proposed approach, and testing the matheuristic on particularly hard realistic scenarios.
The computational experiments show the efficacy and the efficiency of the proposed approach
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
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