1,720,962 research outputs found
Heuristics for the hub location and network designproblem with a mixed vehicle fleet
No full textTwo heuristics are considered to solve the hub location and network design problem with a mixed vehicle fleet, namely, Genetic Algorithms and Simulated Annealing. The uncapacitated single and multiple allocation problem is solved. Several extra features are added to this problem, namely, direct connections, stopovers, and three hubs on a route.OptimizationElectrical Engineering, Mathematics and Computer Scienc
Designing Express Networks with Multi-Agent Modelling
No full textThe ORTEC Consulting Group (OCG) advises express service providers on efficient network design. A part of the challenge to this design is the hub location problem (HLP). The HLP consists of selecting optimal locations for large sorting centres (hubs) from a range of smaller sorting centres (depots) to which the rest of these depots can connect. The resulting network aims to transport parcels in the most cost effective manner achievable. The OCG is interested in multi-agent modelling technique as a new approach to the HLP, since this technique provides a natural way of modelling complexity that arises from interacting nodes. Literature showed no research on solving the HLP from a multi-agent systems (MAS) perspective. This thesis aims to fill this gap. With the main research goal being "Designing a model that can solve the hub location problem for express networks with use of multi-agent modelling", the model was designed using the Prometheus methodology. The model uses information on the volume distributions of a set of fixed depots to determine optimal hub locations from these depots. Simultaneously, the model ensures that parcels can be sent from any location and will be delivered within the set service time. Optimal hub locations in this sense means that the total network cost consisting of hub cost and transport cost is as low as possible. The inputs of the designed model are the depot locations, their volume distributions, the driving times between nodes, hub cost and transport cost. The outputs are the network cost, the number of hubs, the locations of these hubs and the routes of all the different parcels. The designed MAS consists of three main phases. Phase 1 is responsible for creating hubs based on volume distributions. Hubs are placed in regions that have a lot of parcels to be transported between them. Phase 2 creates routes via the hubs that resulted from Phase 1. Although the most efficient routes are calculated, the main focus of this phase is to create routes for every parcel in the first place. During Phase 3 the main focus is cost reduction through reducing air transport cost, reducing road transport cost and reducing hub cost. In addition, part of this design is implemented into a proof of concept using the JACK Agent Language (a Java based language) to show the added value of multi-agent modelling. This proof of concept, Preliminary Organisation of Hub Location Tool (POHST), contains the implementation of the first part of Phase 1. Hence, it creates hubs based on the volume distribution. A graphical user interface is added to turn POHST into an easily accessible tool. This tool is applied to two datasets to demonstrate its use in the preliminary phase of network research aiding in data gathering and the generation of initial hub configurations. Experts of the OCG confirmed the usefulness of POHST as strategic analysis tool. In addition, the type of model outputs did not allow for thorough integral testing of the tool, although other verification methods showed that the tool behaved as intended by the model design. Due to the lack of quantitative output, the tool could not be validated using traditional methods. Instead, the same experts were asked to validate the model. Although they had quite a few recommendations for further improvement of the tool, there was a consensus on its validity. The design process revealed interesting benefits and drawbacks of using the agent paradigm to solve the HLP. The source of much of the complexity of the HLP is the interaction between nodes. One of the major advantages of using the agent paradigm is that it provides a natural way of modelling such interactions. Furthermore, the scalability of agent models is an attractive feature. When a few types of agents have been designed, an unlimited amount of such agents can be used when applying the model, scaling along with the inserted data. Next, the research shows the benefit of agents adapting to local circumstances. By locally looking around for inefficiencies agents are capable to enhance the solution with limited data. Another advantage of using agents is the detailed level of statistics gathering it enables. Every agent decision can be tracked. Consequently, an agent model does not only produce an outcome, it can also show how and why this outcome evolved as it did. The major challenge of using agents to solve the HLP is the difficulty of making local decisions that might impact the entire infrastructure. To be absolutely sure that a local change will lead to lower network cost, all possible consequences are checked and valued for their change in cost. This process can lead to a vast amount of communication, because the agents are practically considering global data. Thus, undermining the multi-agent modelling values of local data views. Although this risk exists in the presented model, it does not prove that it is impossible to achieve a design that reaches a global optimum using strictly local information. However, it is the greatest challenge that the HLP poses to the use of multi-agent modelling. In conclusion, it can be said that this research has proved the potential of using MAS to solve the HLP. It is also certain that many interesting properties of agents can be further investigated. Subsequently, these models could add great value to compete with and possibly even defeat current HLP models.Systems Engineering, Policy Analysis and ManagementSystems EngineeringTechnology, Policy and Managemen
The design of road and air networks for express service providers
Get PDFExpress service providers move packages (i.e. parcels, documents, or pieces of freight) from senders to receivers under various but guaranteed service level agreements. These service level agreements specify date and time of collection at the sender, and receiving at the customer. Research in this dissertation is dedicated to the design of so-called express line-haul transports from the first consolidation point, the origin depot, to the last consolidation point, the destination depot. The line-haul transport is commonly organized either via road or via air. Hub locations are used to sort packages of incoming line-hauls, and to consolidate and load these packages on the outgoing line-hauls. The strategic network design problem is concerned with decisions on these hub locations in the network: how many hubs are needed and where should these be located, and which line-hauls are unloaded and loaded at each hub location? The tactical planning level at express service providers contains decisions on package routings from origin to destination and asset usages. This dissertation focusses on the design of the strategic and tactical line-haul network for road transport in Part I of this dissertation and deals with similar topics for air transport in Part II of this dissertation. In the concluding chapters we present a general review of strategic and tactical network design for express service providers and point to directions for future research
The design of road and air networks for express service providers
No full textExpress service providers move packages (i.e. parcels, documents, or pieces of freight) from senders to receivers under various but guaranteed service level agreements. These service level agreements specify date and time of collection at the sender, and receiving at the customer. Research in this dissertation is dedicated to the design of so-called express line-haul transports from the first consolidation point, the origin depot, to the last consolidation point, the destination depot. The line-haul transport is commonly organized either via road or via air. Hub locations are used to sort packages of incoming line-hauls, and to consolidate and load these packages on the outgoing line-hauls. The strategic network design problem is concerned with decisions on these hub locations in the network: how many hubs are needed and where should these be located, and which line-hauls are unloaded and loaded at each hub location? The tactical planning level at express service providers contains decisions on package routings from origin to destination and asset usages. This dissertation focusses on the design of the strategic and tactical line-haul network for road transport in Part I of this dissertation and deals with similar topics for air transport in Part II of this dissertation. In the concluding chapters we present a general review of strategic and tactical network design for express service providers and point to directions for future research. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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