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Many online platforms rely on users to voluntarily provide content. What motivates users to contribute content for free, however, is not well understood. In this paper, we use a revealed-preference approach to show that career concerns play an important role in user contributions to Stack Overflow, the largest online question-and-answer community. We investigate how activities that can enhance a user’s reputation vary before and after the user finds a new job. We contrast this reputation-generating activity with activities that do not improve a user’s reputation. After finding a new job, users contribute 23.7% less in reputation-generating activity; by contrast, they reduce their non–reputation-generating activity by only 7.4%. These findings suggest that users contribute to Stack Overflow in part because they perceive such contributions as a way to improve future employment prospects. We provide direct evidence against alternative explanations such as integer constraints, skills mismatch, and dynamic selection effects. This paper was accepted by Chris Forman, information systems.

Cet article se propose d’analyser l’évolution de l’imaginaire informatique entre la fin des années 80 et les années 2010 au travers de l’étude de deux mondes fictionnels de jeu de rôle appartenant au genre du cyberpunk : Cyberpunk et Shadowrun. Après une rapide présentation de ces deux mondes fictionnels, il se livre dans un premier temps à l’étude des évolutions de l’imaginaire informatique constatées entre les différentes éditions de ces jeux afin de souligner deux idées importantes : la révolution que constitue un monde informatique sans fil et le paradoxe entre une démocratisation et une complexification de l’informatique. Dans un second temps, il s’efforce de dégager les grandes permanences de cet imaginaire informatique en montrant qu’il se cristallise autour des notions de capitalisme, de puissance, de violence et d’une étrange similitude entre magie et informatique. This paper aims to study how computer imaginary evolved from the end of the eighties until our days. To achieve this, we’ll scrutinize two famous cyberpunk pen and paper role playing game’s fictional worlds : Cyberpunk and Shadowrun. After a short description of those fictional worlds, we’ll study how computer imaginary evolved through the many editions of those RPG to emphasize two main ideas : the revolution of wireless hardware and the paradoxical democratization and complexity of computers. After which, we’ll show the permanence and consistency of some notions and representations : how computers are linked to capitalism and the idea of power or violence, and how computers are often related to the idea of magic.

International audience; This paper introduces the Halphen distribution family for modeling travel time distributions and their reliability on single road links. This probability family originally used in hydrology has a set of relevant characteristics. It is composed of three probability distribution functions for which the mathematical properties are described here. The paper uses a graphical representation, the δ-Moment Ratio Diagram (δ-MRD). This tool allows characterizing travel time reliability as well as selecting best distribution candidates within the fitting processes, by considering empirical data sets. A systematic methodology is developed to take advantage of both aspects. From maximum log-likelihood estimation it is shown that Halphen distributions are amongst the best state-of-the-art solutions for the travel time modeling purpose. This global framework is validated using two empirical data sets: an urban data set gathered in Portland, Oregon (USA) and a periurban data set from Lyon (France). The model calibration is eased through the use of the δ-MRD; this property opens new research directions about the mapping between traffic states and statistical modeling. It comes out from all these considerations that the Halphen family is suitable to describe accurately the travel time dynamics on single links. Therefore it could be part of a decision support system for practitioners interested in travel time variability.

National audience; In the last few years, many works have been done in order to ensure interoperability between applications. Enterprise applications integration and the opening of information systems towards integrated access have been the main motivation for the interest around systems interoperability. In this Paper, an MDA based approach for interoperability is proposed. The MDA is an approach for systems development, which increases the power of models in that work. It provides a means for using models for better understanding, designing, constructing, deploying, operating, maintaining and modifying systems. The three primary goals of MDA are portability, interoperability and reusability. In this paper we apply the MDA as a formal base that supports our approach for interoperability between different information systems

This paper puts forward a new methodology to characterize and compare the examination practice of patent offices. The methodology codifies public information into a typology of chronological key ex...

International audience; This paper proposes a new construction of rate-adaptive coding schemes based on Low Density Parity Check (LDPC) codes for Slepian Wolf source coding. Unlike standard rate-adaptive source coding schemes, the code construction we propose is based on finite-length code design tools that permit to greatly improve the decoding performance at short to moderate length. In particular, our method permits to limit the number of short cycles in the codes at all rates of interest, and to avoid eliminating some source bits from the code constraints. The proposed method shows a performance improvement of up to an order of magnitude at almost all the considered rates compared to the standard LDPCA construction.

International audience; Ridesharing is often viewed as a way to solve urban transport crisis but fails to become an effective widespread practice in the population. We show in this paper that a behavioral approach allows the consideration of sociological and psychological factors which constitute major challenges to the adoption of this practice. We deduct several hypotheses for promoting massification, finding incentives and enabling trust that we propose to explore with field experiments.; Le covoiturage est souvent cité comme solution à la saturation des transports urbains mais reste une pratique marginale dans la population. Nous montrons dans ce papier qu’une approche comportementale permet la prise en compte de facteurs sociologiques et psychologiques qui constituent des freins majeurs à l’adoption de cette pratique. Nous en déduisons plusieurs hypothèses sur le passage à l’échelle, les incitations et la confiance que nous proposons d’explorer par des expérimentations de terrains.

International audience; This paper proposes a method to understand saturation in the railways. It will be applied to the case of Lyon‐Paris High‐Speed Line. The method presented enables to test and compare different solutions to cope with saturation. It can be considered as both a tool for decision‐makers and a support to investment choices.; Ce papier propose une méthode pour conceptualiser la saturation d’une infrastructure ferroviaire. Elle est appliquée au cas de la Ligne à Grande Vitesse Paris‐Lyon et permet de tester et comparer plusieurs pistes de désaturation. Cette méthode peut être considérée comme un outil de décision au service des politiques publiques pour guider le choix en investissements.

Urban governments tend to pedestrianise the centres of cities or to implement street designs which reduce the amount of cars in the public spaces of these centres: pedestrian areas, reduction of on-street parking, implementation of 'zones de rencontre' (living streets), etc. Prima facie, these policies, which encourage pedestrian mobility to the detriment of automotive mobility, seem to be obviously favourable to the preservation of environment. In France, pedestrianisation is presented by the national authorities as one of the tools contributing to the sustainable development of urban territories. Another hypothesis, however, is that these policies are part of urban marketing strategies of cities engaged in inter-urban competition processes - which lead to increase the value and attractiveness of strategic places in the city and tend to displace problems (and deprived populations) to other parts of the urban territory. Thus, as a whole, these policies would not really contribute to sustainable development. Referring to theoretical frameworks related to the entrepreneurial mutation of urban policies, this paper presents an overview of research and empirical results dealing with the implementation and effects of pedestrianisation or other policies in favour of pedestrians in city centres. As a whole, this material gives some credit to the latter hypothesis.; Les gouvernements urbains tendent à piétoniser les centres-villes ou à mettre en oeoeuvre des conceptions de voirie réduisant la quantité d'automobiles dans les espaces publics de ces quartiers centraux : aires piétonnes, réduction du stationnement sur la voirie, aménagement de « zones de rencontre », etc. À première vue, ces politiques, qui assurent la promotion des déplacements à pied au détriment des déplacements motorisés, semblent à l'évidence être favorables à la préservation de l'environnement. La piétonisation est d'ailleurs présentée par l'État comme l'un des instruments contribuant au développement durable des territoires urbains. Cependant, une autre hypothèse est qu'elles participent de stratégies de marketing urbain de villes engagées dans des processus de compétition inter-territoriale - qui conduisent à accroître la valeur et l'attractivité de lieux stratégiques de la ville et tendent à déplacer les problèmes (et les populations défavorisées) vers les autres parties du territoire urbain. Ainsi, globalement, ces politiques n'apporteraient pas de réelle contribution au développement durable. Se référant à des cadres théoriques relatifs à la mutation entrepreneuriale des politiques urbaines, cet article présente un aperçu de recherches et résultats empiriques traitant de la mise en oeoeuvre et des effets d'opérations de piétonisation ou d'autres politiques en faveur des piétons dans les centres-villes. Dans leur ensemble, les éléments rassemblés accréditent plutôt la seconde hypothèse.

International audience; A special session on High-Speed Rail (HSR) and regional and urban growth was organised at the 49th French-speaking Regional Science Association (ASRDLF) Annual Conference (Belfort, 9-11 July 2012). It consisted of two sub-topics. The first was an historical approach of the interactions between transport facilities and territorial dynamics. The second was focused on the cross-relationships between HSR, tourism and territory. This special issue of RTS is a selection of papers presented during this special session.; Le XLIXe colloque de l’ASRDLF, qui s’est déroulé à Belfort du 9 au 11 juillet 2012, a donné lieu à une session spéciale sur le thème « Grande vitesse ferroviaire et développement régional et urbain » avec deux axes consacrés respectivement à la mise en perspective historique des interactions entre infrastructures de transport et dynamiques territoriales et à la question des liens croisés entre TGV, tourismes et territoires. C’est à partir d’une sélection des communications qui ont été présentées que ce numéro spécial est construit.

International audience; What are the interindividual relationships involved in periurban journeys and what is their outcome? Do they create a sense of collective solidarity? Do they concern particular types of journey? These are the issues raised in this paper. Based on a qualitative analysis of space and time in relation to journeys taken by inhabitants using public transport or car‐sharing within the Grenoble district (France), we show that journeys between home and work play a dual role of buffer and link between the spheres of daily life, because they cover a range of uses and social interactions. The notion of sharing not only a passenger compartment and standards and rules of interaction but also a sense of collective solidarity, rooted as much in everyday space (home, workplace) as in the experience of the journey itself, leads us to define an identity of movement. This includes a feeling of recognition and belonging based on sharing the same material conditions and ideals of transport, central to the understanding of the individual and collective organization of journeys.; Quelles sont les relations interindividuelles en jeu dans la mobilité périurbaine et que produisent‐elles ? Fabriquent‐elles des solidarités collectives ? Définissent‐elles des modalités de déplacements particulières ? Tel est le questionnement et l’objet de cette contribution. Partant d’une analyse qualitative des espaces‐temps de la mobilité dans le moyen‐Grésivaudan (Grenoble, France), auprès d’habitants recourant aux transports en commun ou au covoiturage, nous montrons que les trajets domicile‐travail jouent un double rôle de sas et de lien entre les sphères du quotidien parce qu’ils sont investis d’une diversité d’usages et d’interactions sociales. Le partage d’un même habitacle, de normes et de règles d’interactions mais aussi de solidarités collectives ancrées tout autant dans les territorialités habituelles (résidence, travail) que dans l’expérience de mobilité nous amène à définir une identité de mouvement. Cette dernière qualifie un sentiment de reconnaissance et d’appartenance fondé sur le partage des mêmes conditions matérielles et idéelles de déplacement, au cœur de la compréhension de l’organisation individuelle et collective des mobilités.

The probability hypothesis density (PHD) methodology is widely used by the research community for the purposes of multiple object tracking. This problem consists in the recursive state estimation of several targets by using the information coming from an observation process. The purpose of this paper is to investigate the potential of the PHD filters for real-time traffic state estimation. This investigation is based on a Cell Transmission Model (CTM) coupled with the PHD filter. It brings a novel tool to the state estimation problem and allows to estimate the densities in traffic networks in the presence of measurement origin uncertainty, detection uncertainty and noises. In this work, we compare the PHD filter performance with a particle filter (PF), both taking into account the measurement origin uncertainty and show that they can provide high accuracy in a traffic setting and real-time computational costs. The PHD filtering framework opens new research avenues and has the abilities to solve challenging problems of vehicular networks.

This paper deals with the presentation of different multi-user detectors in the Universal Mobile Telecommunications System (UMTS) context. The challenge is always to optimize the compromise between performance and complexity. Compared with the solution commonly used today, the rake detector, successive interference cancellation (SIC) detector has better performance despite its higher complexity. Our innovative solution proposes joining detector and channel turbo decoder to get a significant gain in terms of performance. Furthermore, when detection and decoding are implemented in a single function, complexity does not increase much.

The paper investigates information sharing communities. The environment is characterized by the anonymity of the contributors and users, as on the Web. It is argued that a community may be worth forming because it facilitates the interpretation and understanding of the posted information. The admission within a community and the stability of multiple communities are examined when individuals differ in their tastes., Le papier étudie la formation de communautés partageant des informations dans un environnement qui est caractérisé par l'anonymat des utilisateurs et contributeurs à l'instar du Web. L'analyse est basée sur la valeur de l'information au sens de Blackwell (1953). Nous examinons le choix des critères d'admission dans une communauté et la stabilité des communautés dans un modèle de divergence de goûts.

In this paper, we study the french adverbs of completion totalement, complètement, entièrement and intégralement in the verbal domain, from a semantic point of view. Following Tenny (2000), we argue that completion adverbs with a quantitative value can only modify telic predicates (*regarder totalement le tableau / détruire totalement une ville). We also identify a qualitative use which doesn’t impose such a constraint (avoir totalement raison). Then, through the analysis of real exemples and of their typical context, we discuss the semantic properties of these different adverbs that are related in various ways to the expression of completion.

Collective awareness has been advocated as critical to the successful introduction and use of groupware systems and therefore in supporting virtual collaboration. To date, however, no study has attempted to develop a scale for measuring the awareness levels in the context of virtual teams. In this paper, we report on the development of a measurement scale that captures the degree of collective awareness in virtual teams. The instrument measures two dimensions of awareness: activity awareness and social awareness. We follow a rigorous empirical scale development process to create a bidimensional measurement scale that exhibits satisfactory levels of reliability and validity. The classic indicators of validation confirm the inclusive nature of collective awareness based on the two dimensions suggested. The instrument should prove useful to virtual teams as it provides an aggregate measure of the degree of their awareness. This instrument equally facilitates an evaluation of interactive systems' user-friendliness, based on their ability to maintain user awareness.

If projects are usually dichotomised between qualitative and quantitative research, the aims of this paper is to underline the role of computer assisted qualitative data analysis software (CAQDAS). The literature on CAQDAS expresses both hopes and fears and CAQDAS are just another tool. This article underlines that software may lead to a deep understanding of a specific organization and can also contribute to enrich qualitative analysis process and reduce the ideologic gap between quantitative and qualitative methods.

International audience; This paper presents our research into intelligent agentsbased Human-Computer interactions. Our goal is to design personalized information systems. For that, the aim of their intelligent interfaces is to understand the users needs, to identify his/her preferences and, to satisfy his/her expectations.We then propose to design the interfaces with intelligent agents. This research is applied to traveler information design in transportation systems (Predit Agen- Perso project).