Univ., Diss.--Karlsruhe, 2007.

Ecole Polytechnique Federale, Diss.--Lausanne, 2007.

Zugl.: Vallendar, WHU - Otto Beisheim School of Management, 2008.

Zugl.: Göttingen, Universiẗat, Diss., 2008.

ENGLISH ABSTRACT: It is very seldom that a decision-making problem concerns only a single value or objective. The process of simultaneously optimising two or more con icting objectives is known as multi-objective optimisation (MOO). A number of metaheuristics have been successfully adapted for MOO. The aim of this study was to investigate the feasibility of applying an agent-based modelling approach to MOO. The (s; S) inventory problem was chosen as the application eld for this approach and Anylogic used as model platform. Agents in the model were responsible for inventory and sales management, and had to negotiate with each other in order to nd optimal reorder strategies. The introduction of concepts such as agent satisfaction indexes, aggression factors, and recollection ability guided the negotiation process between the agents. The results revealed that the agents had the ability to nd good strategies. The Pareto front generated from their proposed strategies was a good approximation to the known front. The approach was also successfully applied to a recognised MOO test problem proving that it has the potential to solve a variety of MOO problems. Future research could focus on further developing this approach for more practical applications such as complex supply chain systems, nancial models, risk analysis and economics. / AFRIKAANSE OPSOMMING: Daar is weinig besluitnemingsprobleme waar slegs 'n enkele waarde of doelwit ter sprake is. Die proses waar twee of meer doelwitte, wat in konflik staan met mekaar, gelyktydig optimiseer word, staan bekend as multi-doelwit optimisering (MOO). 'n Aantal metaheuristieke is al suksesvol aangepas vir MOO. Die doelwit van hierdie studie was om ondersoek in te stel na die lewensvatbaarheid van die toepassing van 'n agent gebasseerde modelerings benadering tot MOO. As toepassingsveld vir hierdie benadering was die (s; S) voorraad probleem gekies en Anylogic was gebruik as model platform. In die model was agente verantwoordelik vir voorraad- en verkope bestuur. Hulle moes onderling met mekaar onderhandel om die optimale bestelling strategiee te verkry. Konsepte soos agentbevrediging, aggressie faktore en herinneringsvermoens is ingestel om die onderhandeling tussen die agente te bewerkstellig. Die resultate het gewys dat die agente oor die vermoe beskik om met goeie strategiee vorendag te kom. Die Pareto fronte wat gegenereer is deur hul voorgestelde strategiee was 'n goeie benadering tot die bekende front. Die benadering was ook suksesvol toegepas op 'n erkende MOO toets-probleem wat bewys het dat dit oor die potensiaal beskik om 'n verskeidenheid van MOO probleme op te los. Toekomstige navorsing kan daarop fokus om hierdie benadering verder te ontwikkel vir meer praktiese toepassings soos komplekse voorsieningskettingstelsels, finnansiele modelle, risiko-analises en ekonomie.

En ce début de XXIe siècle, le vin et la vigne constituent une richesse importante pour bon nombre de pays. Les territoires viticoles, tout en conservant leurs qualités d'espace de production, développent des stratégies d'adaptation à la globalisation du marché et aux attentes des consommateurs toujours plus versatiles. Or en raison de conditions orographiques particulières, les territoires de montagne et de fortes pentes voient leurs marges de manœuvre réduites. En effet, une grosse partie de leurs coûts de production reste bien souvent incompressible par rapport à la viticulture de plaine. Paradoxalement ces paysages viticoles, image du construit social et des équilibres environnementaux, participent à leur reconnaissance internationale. Le travail présenté ici est né en réponse à la sensibilité croissante de ces vignobles de fortes pentes. En nous appuyant sur deux territoires d'étude, en France le vignoble de la Côte Vermeille et en Italie le val di Cembra, nous questionnons les spécificités de la viticulture de fortes pentes. Notre approche met l'accent sur les possibilités offertes par des méthodes empiriques de modélisation à base d'agents pour proposer un regard renouvelé sur le rôle des interactions société-environnement dans le maintien et le développement de ces territoires sous contraintes. A travers une constellation de modèles multi-agents issus des questionnements récurrents des acteurs de la filière, et selon une démarche exploratoire et incrémentale, nous nous intéresserons ici à trois grands types de questions posées aux territoires viticoles de fortes pentes. Le premier concerne la place du marché et ses conséquences sur les dynamiques de couvert végétal à petite échelle. Le second type de questionnement explore également les dynamiques spatiales du couvert végétal, mais se place à mezzo-échelle, et propose de s'intéresser à la définition des règles socio-économiques simples qui sous-tendent les dynamiques foncières à l'échelle de quelques communes. Enfin le dernier volet de ce travail se place à grande échelle et s'intéresse à des phénomènes très descriptifs. L'ensemble de ces réflexions nous amènera ensuite à utiliser la modélisation co-construite avec les acteurs pour proposer une vision prospective globale pour les territoires de montagne et de fortes pentes. Cette approche prospective sera conduite en parallèle avec certains acteurs de la filière ce qui nous permettra de délimiter les variables structurelles propres aux systèmes de fortes pentes telles qu'elles sont ou non vécues par les acteurs. Basés sur la délimitation de ces variables, nous proposons enfin quatre scenarii prospectifs pour la viticulture en fortes pentes. / Wine and wineyards stand nowadays as a significant wealth for a number of countries. While retaining their properties as production space, vine-growing regions are developing adaptation strategies to market globalisation and to the ever more versatile consumer expectations. Yet, due to the corresponding specific orographic conditions in steep slope and mountain regions, actor's relative leeway is reducing ,. Comparatively to plain wine-growing, a large part of their production costs often remains indeed incompressible. On the other hand, these vine-growing landscape take advantage of such harsh conditions in terms of international recognition, as images of social construct and environmental equilibrium. The work presented here emerged as a response to this steep slope vineyards' sensitivity. This investigation relies on two study areas: the Côte Vermeille vineyards in France, and the val di Cembra in Italy. Our approach focuses on the opportunities granted by agent-based empirical modelling methods, in order to put forward a renewed look at the role of society-environment interactions in the sustainability and development of territories subject to constraints. Using an exploratory and incremental method, three significant issues of steep slope vine-growing regions have been addressed, thanks to a constellation of multi-agent models, derived from questioning actors of this sector. The first considers the market's impacts on the small-scale plant cover dynamics. The second issue focuses on meso-scale plant cover dynamics and questions the definition of simple socio-economic ruleset, within the frame of land property dynamics and applied to the scale of a few municipalities. The last section of this work is dedicated to some descriptive phenomena within a large scale. Thus, the sum of these reflections leads us to exploit co-designed modelling with the stakeholders in order to propose a global prospective vision for mountain and steep slope regions. This prospective approach is conducted in association with some of the players in the sector, thus allowing us to delineate the structural variables linked to steep slope vineyards' systems in agreement with their experience. Based on these delineated variables, four prospective scenarii are put forward for the steep slope vine-growing activity.

Through social learning, animals acquire information from others, such as skills and knowledge about the environment. High fidelity transmission of locally adaptive information can lead to population-specific traits, or cultural traits, which are fundamental to the emergence of culture. Despite social learning being widespread in the animal kingdom, culture is rare in nature. This thesis investigates the evolution, ecology, and dynamics of social learning, to increase our understanding why species differ in their ability to generate and accumulate cultural traits, and ultimately how complex human culture emerged. Chapter 2 introduces a novel computational model that explicitly incorporates competition into the social learning context. The model predicts that social learning is most adaptive where resources are unevenly distributed and stable through time, even if individuals compete for limited resources. The model provides an explanation for reports of animals disregarding social information, even if it is available. Testing these predictions Chapter 3 presents a bumblebee foraging experiment. The results support the theoretical predictions, showing that foragers use social information to find rewarding flowers, even if social cues indicate competition. Chapter 4 further examines the trade-off between access to social information and competition. Individuals that are central in a learning network have more opportunities to acquire information from others, but also face an increased likelihood to engage in competition. The results of this model suggest that across different learning contexts centrality is only beneficial for dominant individuals because dominance can mitigate the effect of competition. This also shows that individual phenotypic differences affect the utility of social information. Chapter 5 uses a dynamic network model approach to tests whether these differences modulate the structure of learning networks and by extension of the population. The model shows that this is the case and that where social learning is favoured by the environment networks are more structured. Chapter 6, studies the drivers behind individual differences in social learning. The chapter focusses on reports of sex differences in social information use and finds that they can be explained by differences in risk taking behaviour. The results highlight the importance of the feedback between learning individuals, and how this shapes social learning dynamics on an individual as well as on a population level.

abstract: Free/Libre Open Source Software (FLOSS) is the product of volunteers collaborating to build software in an open, public manner. The large number of FLOSS projects, combined with the data that is inherently archived with this online process, make studying this phenomenon attractive. Some FLOSS projects are very functional, well-known, and successful, such as Linux, the Apache Web Server, and Firefox. However, for every successful FLOSS project there are 100's of projects that are unsuccessful. These projects fail to attract sufficient interest from developers and users and become inactive or abandoned before useful functionality is achieved. The goal of this research is to better understand the open source development process and gain insight into why some FLOSS projects succeed while others fail. This dissertation presents an agent-based model of the FLOSS development process. The model is built around the concept that projects must manage to attract contributions from a limited pool of participants in order to progress. In the model developer and user agents select from a landscape of competing FLOSS projects based on perceived utility. Via the selections that are made and subsequent contributions, some projects are propelled to success while others remain stagnant and inactive. Findings from a diverse set of empirical studies of FLOSS projects are used to formulate the model, which is then calibrated on empirical data from multiple sources of public FLOSS data. The model is able to reproduce key characteristics observed in the FLOSS domain and is capable of making accurate predictions. The model is used to gain a better understanding of the FLOSS development process, including what it means for FLOSS projects to be successful and what conditions increase the probability of project success. It is shown that FLOSS is a producer-driven process, and project factors that are important for developers selecting projects are identified. In addition, it is shown that projects are sensitive to when core developers make contributions, and the exhibited bandwagon effects mean that some projects will be successful regardless of competing projects. Recommendations for improving software engineering in general based on the positive characteristics of FLOSS are also presented. / Dissertation/Thesis / Ph.D. Computer Science 2011

abstract: Supply chains are increasingly complex as companies branch out into newer products and markets. In many cases, multiple products with moderate differences in performance and price compete for the same unit of demand. Simultaneous occurrences of multiple scenarios (competitive, disruptive, regulatory, economic, etc.), coupled with business decisions (pricing, product introduction, etc.) can drastically change demand structures within a short period of time. Furthermore, product obsolescence and cannibalization are real concerns due to short product life cycles. Analytical tools that can handle this complexity are important to quantify the impact of business scenarios/decisions on supply chain performance. Traditional analysis methods struggle in this environment of large, complex datasets with hundreds of features becoming the norm in supply chains. We present an empirical analysis framework termed Scenario Trees that provides a novel representation for impulse and delayed scenario events and a direction for modeling multivariate constrained responses. Amongst potential learners, supervised learners and feature extraction strategies based on tree-based ensembles are employed to extract the most impactful scenarios and predict their outcome on metrics at different product hierarchies. These models are able to provide accurate predictions in modeling environments characterized by incomplete datasets due to product substitution, missing values, outliers, redundant features, mixed variables and nonlinear interaction effects. Graphical model summaries are generated to aid model understanding. Models in complex environments benefit from feature selection methods that extract non-redundant feature subsets from the data. Additional model simplification can be achieved by extracting specific levels/values that contribute to variable importance. We propose and evaluate new analytical methods to address this problem of feature value selection and study their comparative performance using simulated datasets. We show that supply chain surveillance can be structured as a feature value selection problem. For situations such as new product introduction, a bottom-up approach to scenario analysis is designed using an agent-based simulation and data mining framework. This simulation engine envelopes utility theory, discrete choice models and diffusion theory and acts as a test bed for enacting different business scenarios. We demonstrate the use of machine learning algorithms to analyze scenarios and generate graphical summaries to aid decision making. / Dissertation/Thesis / Ph.D. Industrial Engineering 2012

O modelo apresentado neste trabalho, denominado SimPed, foi concebido para fornecer uma boa representação da interação entre pedestres e uma abordagem realista para a interação entre pedestres e veículos em ambiente urbano. O modelo apresenta uma estrutura híbrida, combinando conceitos baseados em campo de força e as abordagens baseadas regra. Pedestres e veículos são representados por agentes e os atributos das infraestruturas são definidos através de camadas estruturais. Este trabalho, apresenta também, o desenvolvimento de dois modelos preliminares ao SimPed. O primeiro modelo apresenta conceitos básicos de movimento de pedestres. O segundo refere-se aos problemas de geração de rotas dos pedestres. O modelo SimPed é um novo modelo de movimentação de pedestres, que considera a interação entre veículos e pedestres. A fim de verificar a aplicabilidade prática do SimPed, este trabalho apresenta três testes de simulação. O primeiro teste preocupa-se com a capacidade do modelo para representar a interação entre os pedestres. O segundo analisa uma travessia de pedestres, e foi concebido para investigar a influência do campo de força dos pedestres no desempenho do tráfego de veículos. O terceiro teste se preocupa com a representação da aceitação de gaps pelos pedestres. Neste teste os valores dos gaps obtidos na simulação são comparados com valores de gaps obtidos a partir de uma coleta de dados de vídeo em um local de travessia de pedestres. Os testes indicam que o modelo SimPed fornece bons fundamentos para uma representação de qualidade do processo de travessia dos pedestres. / The model presented in this work, named as SimPed, has been devised to provide a sound representation of interaction among pedestrians and a more realistic approach for interaction between pedestrians and vehicles. The model presents a hybrid structure, combining force field and rule based approaches. Pedestrians and vehicles assume an agent based representation and the attributes of the infrastructure are defined by several structural layers. This work presents the development of 2 preliminary models and the SimPed model. The first model concerns about basic concepts of pedestrians’ movement. The second one concerns about the pedestrians’ path generation problem. The SimPed model is a new pedestrian’s movement model with vehicle and pedestrians interaction capabilities. In order to verify the practical applicability of the SimPed, this work presents three simulation tests. The first test concerns the capacity of the model to represent interaction among pedestrians. The second analyses a pedestrian crossing environment, and was devised to investigate the influence of the force-based parameter on traffic performance. The third simulation test is concerned with pedestrians´ gap acceptance representation. In this test gap acceptance values obtained from simulation are compared with gap values obtained from a video data collection of pedestrians at a crossing facility. The tests indicate that the model structure and its calibration resources provide good grounds for sound representations of realistic conditions.