Les espaces publics dans les territoires de densités intermédiaires : conceptions, usages et potentialités

National audiencePublic spaces in periurban areas often have a poor image. They are considered either as insufficiently developed, or as emblematic of privatised town development. To overcome this simplistic vision, and in order to understand the specificity of these areas, this article seeks to distance itself both from a “periurban” reading of these areas and from an “urban-centred” view of public spaces. Based on a survey conducted in the northern outskirts of the Paris region, it highlights the design logic of public authorities, as well as the convergences and discrepancies with the inhabitants’ behaviour. Finally it puts forward some possibilities for action.Souvent perçus négativement, les espaces publics périurbains sont considérés soit comme insuffisamment développés, soit comme emblématiques de la ville privatisée. Pour sortir de cette vision réductrice et en saisir la spécificité, cet article entend prendre ses distances par rapport à une lecture « péri-urbaine » de ces territoires et à une lecture « urbano-centrée » des espaces publics. À partir d’une enquête menée sur les franges nord de l’agglomération parisienne, elle met en évidence les logiques de conception véhiculées par les pouvoirs publics, les convergences et les décalages avec les pratiques des habitants, avant de proposer quelques pistes pour l’action

Mandator and Sporades: Robust Wide-Area Consensus with Efficient Request Dissemination

Consensus algorithms are deployed in the wide area to achieve high availability for geographically replicated applications. Wide-area consensus is challenging due to two main reasons: (1) low throughput due to the high latency overhead of client request dissemination and (2) network asynchrony that causes consensus protocols to lose liveness. In this paper, we propose Mandator and Sporades, a modular state machine replication algorithm that enables high performance and resiliency in the wide-area setting. To address the high client request dissemination overhead challenge, we propose Mandator, a novel consensus-agnostic asynchronous dissemination layer. Mandator separates client request dissemination from the critical path of consensus to obtain high performance. Composing Mandator with Multi-Paxos (Mandator-Paxos) delivers significantly high throughput under synchronous networks. However, under asynchronous network conditions, Mandator-Paxos loses liveness which results in high latency. To achieve low latency and robustness under asynchrony, we propose Sporades, a novel omission fault-tolerant consensus algorithm. Sporades consists of two modes of operations -- synchronous and asynchronous -- that always ensure liveness. The combination of Mandator and Sporades (Mandator-Sporades) provides a robust and high-performing state machine replication system. We implement and evaluate Mandator-Sporades in a wide-area deployment running on Amazon EC2. Our evaluation shows that in the synchronous execution, Mandator-Sporades achieves 300k tx/sec throughput in less than 900ms latency, outperforming Multi-Paxos, EPaxos and Rabia by 650\% in throughput, at a modest expense of latency. Furthermore, we show that Mandator-Sporades outperforms Mandator-Paxos, Multi-Paxos, and EPaxos in the face of targeted distributed denial-of-service attacks

RACS and SADL: Towards Robust SMR in the Wide-Area Network

Consensus algorithms deployed in the crash fault tolerant setting chose a leader-based architecture in order to achieve the lowest latency possible. However, when deployed in the wide area they face two key robustness challenges. First, they lose liveness when the network is unreliable because they rely on timeouts to find a leader. Second, they cannot have a high replication factor because of the high load imposed on the leader-replica making it a bottleneck. This effectively limits the replication factor allowed, for a given level of throughput, thus lowering the fault tolerance threshold. In this paper, we propose RACS and SADL, a modular state machine replication algorithm that addresses these two robustness challenges. To achieve robustness under adversarial network conditions, we propose RACS, a novel crash fault-tolerant consensus algorithm. RACS consists of two modes of operations: synchronous and asynchronous, that always ensure liveness. RACS leverages the synchronous network to minimize the communication cost to O(n) and matches the lower bound of O(n2) at adversarial-case executions. To avoid the leader bottleneck and to allow higher replication factor, without sacrificing the throughput, we then propose SADL, a novel consensus-agnostic asynchronous dissemination layer. SADL separates client command dissemination from the critical path of consensus and distributes the overhead evenly among all the replicas. The combination of RACS and SADL (SADL-RACS) provides a robust and high-performing state machine replication system. We implement and evaluate RACS and SADL-RACS in a wide-area deployment running on Amazon EC2.Comment: arXiv admin note: text overlap with arXiv:2209.0615

Construction interactive de BRDFs par simulation 2D de micro-géométries en couches multiples

Les modèles de réflexion complexes, avec leurs nombreux paramètres dont certains restent non intuitifs, sont difficiles à contrôler pour obtenir une apparence désirée. De plus, même si un artiste peut plus aisément comprendre la forme de la micro-géométrie d'une surface, sa modélisation en 3D et sa simulation en 4D demeurent extrêmement fastidieuses et coûteuses en mémoire. Nous proposons une solution intermédiaire, où l'artiste représente en 2D une coupe dans un matériau, en dessinant une micro-géométrie de surface en multi-couches. Une simulation efficace par lancer de rayons en seulement 2D capture les distributions de lumière affectées par les micro-géométries. La déviation hors-plan est calculée automatiquement de façon probabiliste en fonction de la normale au point d'intersection et de la direction du rayon incident. Il en résulte des BRDFs isotropes complètes et complexes, simulées à des vitesses interactives, et permettant ainsi une édition interactive de l'apparence de réflectances riches et variées.Complex reflection models, with their many parameters, some of which are not intuitive at all, are difficult to control when trying to achieve a desired appearance. Moreover, even if an artist can more easily understand the shape of the surface micro-geometry, its 3D modeling and 4D simulation remain extremely tedious and expensive in memory. We propose an intermediate solution, where the artist represents a 2D cross section of a material, by drawing a multi-layered surface micro-geometry. An efficient 2D ray tracing simulation captures the light distribution specific to those micro-geometries. Off plane deflection is automatically calculated in a probabilistic way, based on the surface normal at the intersection point and the incident ray direction. This results in complete and complex isotropic BRDFs, simulated at interactive rates, and allowing interactive editing of rich and varied materials