322,982 research outputs found
Agent-Based Modelling and Simulation of Safety and Resilience in Air Transportation
No full textPurpose: In order to improve the safety, capacity, economy, and sustainability of air transportation, revolutionary changes are required. These changes might range from the introduction of new technology and operational procedures to unprecedented roles of human operators and the way they interact. Implementing such changes can introduce both negative and positive emergent behaviour. i.e. behaviour that arises from the interactions between system entities as proposed in innovative concepts. Currently, the inability to understand and control such behaviour prevents us from avoiding undesired negative emergent behaviours and promoting positive ones. In order to address this problem, this thesis aims to understand emergent behaviour in the complex socio-technical air transportation system. Methods: The thesis proposes Agent-Based Modelling and Simulation (ABMS) as a method for capturing emergent behaviour of the socio-technical air transportation system, and evaluating novel system designs. The popularity of ABMS is driven by its capability of handling the increasing complexity of real world socio-technical systems that exhibit emergent behaviour. This thesis focuses on two main applications namely: 1) the identification of emergent safety risk of an active runway crossing operation; and 2) the evaluation of the role of coordination in Airline Operations Control (AOC) resilience. In both applications, ABMS has emerged as a key method because it is widely used in complexity science to understand how interactions give rise to emergent behavior. The agent-based models include all relevant human and technical agents, such as pilots and controllers and the decision support systems involved. Simulation of these agents interacting together is conducted to predict the impact of both existing and future concepts of operation. Results: The applications in this thesis highlight that ABMS has the capability to reveal unexpected emergent behaviour and provide novel insights in air transportation. For the airport safety application, various types of emergent behaviour have been revealed due to the development and simulation of the agent-based model that covers the totality of interactions of components and their variability in performance over time. The Monte Carlo simulations make it possible to understand the potential of agents in restricting the risk in off-nominal scenarios, through capturing their stochastic nature and accounting for uncertainty. For the airline resilience application, novel insights were gained about the role of coordination in airline resilience. Capitalizing on established airline practice and research about human coordination from the psychology domain, the agent-based simulations evaluated the operational effects of AOC coordination policies on a challenging disruption scenario. Conclusions & possible applications and implications: This thesis demonstrates that ABMS of air transport operations is a viable approach in gaining knowledge about emergent behaviour which was unknown before. This knowledge includes both bottlenecks of system designs and identified opportunities, and hence can be used to control and further optimize the socio-technical air transportation system. This also implies that ABMS can be a cost-effective method for evaluating new concepts during the early design phase of air transport operations.Air Transport and OperationsAerospace Engineerin
Mediterranean land surfaces under global change : towards a roadmap for sustainable land use in Europe
No full textQuelles agricultures irriguées demain?
No full textL’agriculture irriguée produit plus de 40 % de l’alimentation mondiale sur moins de 20 % des terres cultivées. L’irrigation, qui consiste à agir sur le cycle naturel de l’eau pour conduire et sécuriser les cultures dans des contextes géographiques où les pluies sont soit insuffisantes soit aléatoires, est indispensable à la sécurité alimentaire mondiale sujette au défi démographique. Pour autant, les enjeux d’une agriculture irriguée durable sont multiples pour répondre aux nécessités actuelles et futures : gestion intégrée de la ressource en eau, équité sociale pour les agriculteurs par rapport à l’allocation des terres et de l’eau, viabilité économique et financière des systèmes irrigués, gouvernance de l’eau et institutions adaptées, économie d’eau et valorisation des eaux usées, pratiques agroécologiques pour concilier productivité et défis environnementaux et climatiques, et préservation de la biodiversité, sont autant de dimensions dont il est nécessaire de tenir compte. Cet ouvrage apporte des éclairages sur ces différents défis, à partir de retours d’expériences issus de plusieurs décennies d’actions de développement de l’agriculture irriguée à l’international, conduites en particulier dans le cadre du projet COSTEA (comité scientifique et technique de l’Eau agricole). Il intéressera les décideurs en charge des politiques agricoles et d’irrigation, les opérateurs du développement et toute personne concernée par la pluralité des enjeux de l’agriculture irriguée. Cet ouvrage a été réalisé par un collectif d’auteurs engagés dans le projet COSTEA, et coordonné par S. Bouarfa, F. Brelle et C. Coulon
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Evaluation of a Multi-Agent System approach to airline disruption management
No full textEach day, airlines face disturbances that disrupt their carefully planned operations. Events like adverse weather conditions, sick crew members, or damaged aircraft often result in delays in the airline's schedule. An airline recovers from such disruptions through the role played by its Airline Operations Control (AOC). A Multi-Agent System (MAS) approach to airline disruption management was recently proposed under the acronym MASDIMA (Multi-Agent System for Disruption Management in AOC). The purpose of this paper is to evaluate this MAS supported AOC approach on its performance and its practical introduction. This is done using a scenario-based analysis to compare the MAS supported policy to human-team based AOC policies. A task-based analysis identifies how well AOC is able to cover a set of tasks using the MAS supported policy. The scenario-based analysis shows that the MAS supported AOC is able to find the optimal solution, and to do this significantly faster. The task-based analysis identified two main challenges for implementing the MAS supported AOC policy: i) to overcome the loss of experience that is caused by significantly automating humans roles in AOC, and ii) to reduce the workload for people that remain in AOC after its introduction. The paper concludes that implementing the MAS supported AOC policy leads to both better and faster resolutions, though the replacement of human roles also poses novel challenges that remain to be resolved: a potential increase in workload for the remaining human role and loss of experience in handling exceptional situations.Accepted Author ManuscriptAir Transport & Operation
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Author's address:
No full textCan archives of audiovisual TV interviews be used to make authors more visible to students, and thereby reduce the learning gap between native and non-native language speakers in college classes? We examined students in a college course who learned about one scholar's ideas through watching an audiovisual TV interview (i.e., visible author format) and about another scholar's ideas through reading a formal text description (i.e., invisible author format). For the invisible author, native language speakers scored significantly higher than the non-native language speakers on a corresponding exam question (i.e., a cognitive measure), generated more words on the exam question (i.e., a motivational measure), and mentioned the author's name more often in answering the exam question (i.e., an affective measure). For the visible author, the groups did not differ on any of these measures. These findings provide evidence for the idea that making the author visible through audiovisual TV interviews can eliminate the learning gap between native and non-native language speakers. 3 Universities around the world serve students who are non-native speakers of th
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