The Court of Appeals as the Middle Child

It’s said that middle children are most likely to be forgotten in the chaos of family life. The same could be said of the U.S. Courts of Appeals, which in 2016, mark their 125th anniversary, and which are the middle child of the federal judicial family. As too few people, even academics, know, the courts of appeals were created in 1891 by the Evarts Act, more than a century after the Constitution and the First Judiciary Act. The history of the courts of appeals has accordingly hovered somewhat uneasily next to that of the U.S. Supreme Court and the district courts. Setting aside the rare times when an appellate court strikes down or stays an important national statute or program, our work remains largely below the radar of American public debate. In contrast to our sibling Article III courts, district and Supreme, our intermediate appellate character is stunted in three different ways

Non-random correlation of species dynamics in tropical tree communities

International audienceThe importance of environmental stochasticity for tropical tree dynamics has been recently stressed by several studies. This has spurred the development of a 'time-averaged neutral model' of community dynamics by Kalyuzhny and colleagues that extends the neutral model by incorporating environmental stochasticity. We here show that this framework can be used to assess the presence of non-random correlations between species dynamics. Indeed, the time-averaged neutral model makes the simplifying assumption that species responses to environmental variation are uncorrelated. We therefore propose to use this model as a null hypothesis against which observed community dynamics can be compared. This study makes five contributions. First, we describe a novel time-averaged neutral model of community dynamics that is close to, but more flexible than the one previously proposed by Kalyuzhny and colleagues. Second, we develop an inference method based on approximate Bayesian computation (ABC) and demonstrate the identifiability of the model parameters from community time series data. Third, we develop a test of the significance of environmental stochasticity, and a method to quantify its contribution to population variance. Fourth, we develop a test of non-random correlation between species dynamics. Fifth, we apply these developments to three datasets of tropical tree dynamics. We evidence both a strong contribution of environmental stochasticity to population variance in the three datasets, and a non-random correlation of species dynamics in one of them. We finally discuss the implications of these results for the modelling of tropical tree community dynamics

Multichannel access for bandwidth improvement in IEEE 802.15.4 wireless sensor networks

International audienceIn this paper, we propose a new multichannel allocation protocol for ZigBee/IEEE 802.15.4 networks. The main goal is to improve the global throughput which is basically insufficient to satisfy high bandwidth requirements for applications like monitoring or traffic control. The solution is based on the availability of multiple channels on current low- cost, low-energy radio transceivers, such as TI/Chipcon CC2420, which can be easily tuned dynamically to different frequencies. This possibility can be exploited to increase the number of simultaneous transmissions on adjacent links. The allocation of the different channels is centralized and distributed by the coordinator thanks to a function designed to compute the channel offset between two successive children routers. In the nodes, the switching process between the transmission and the reception channels is triggered starting from the PHY primitive available on the transceiver. The evaluation shows that the proposed protocol improves the global throughput by a factor between 2 and 5, depending on the scenario, compared to the single-channel solution or a random channel allocation

Cross-layer Loss Differentiation Algorithm to Improve TCP Performances in WLANs

International audienceLoss Differentiation Algorithms (LDA) are currently used to determine the cause of packet losses with an aim of improving TCP performance over wireless networks. In this work, we propose a cross-layer solution based on two LDA in order to classify the loss origin on an 802.11 link and then to react consequently. The first LDA scheme, acting at the MAC layer, allows differentiating losses due to signal failure caused by displacement or by noise from other loss types. Moreover, in case of signal failure, it adapts the behavior of the MAC layer to avoid a costly end-to-end TCP resolution. The objective of the second LDA scheme, which acts at the TCP layer, is to distinguish a loss due to interferences from those due to congestions and to adapt consequently the TCP behavior. The efficiency of each LDA scheme and of the whole cross-layer solution are then demonstrated through simulations

Analyse temporelle de la dynamique de communautés végétales à l'aide de modèles individus-centrés

Plant communities are complex systems in which multiple species differing by their functional attributes interact with their environment and with each other. Because of the number and the diversity of these interactions the mechanisms that drive the dynamics of theses communities are still poorly understood. Modelling approaches enable to link in a mechanistic fashion the process driving individual plant or population dynamics to the resulting community dynamics. This PhD thesis aims at developing such approaches and to use them to investigate the mechanisms underlying community dynamics. We therefore developed two modelling approaches. The first one is based on a stochastic modelling framework allowing to link the population dynamics to the community dynamics whilst taking account of intra- and interspecific interactions as well as environmental and demographic variations. This approach is easily applicable to real systems and enables to describe the properties of plant population through a small number of demographic parameters. However our work suggests that there is no simple relationship between these parameters and plant functional traits, while they are known to drive their response to extrinsic factors. The second approach has been developed to overcome this limitation and rely on the individual-based model Nemossos that explicitly describes the link between plant functioning and community dynamics. In order to ensure that Nemossos has a large application potential, a strong emphasis has been placed on the tradeoff between realism and parametrization cost. Nemossos has then been successfully parameterized from trait values found in the literature, its realism has been demonstrated and it has been used to investigate the importance of temporal environmental variability for the coexistence of functionally differing species. The complementarity of the two approaches allows us to explore various fundamental questions of community ecology including the impact of competitive interactions on community dynamics, the effect of environmental filtering on their functional composition, or the mechanisms favoring the coexistence of plant species. In this work, the two approaches have been used separately but their coupling might offer interesting perspectives such as the investigation of the relationships between plant functioning and population dynamics. Moreover each of the approaches might be used to run various simulation experiments likely to improve our understanding of mechanisms underlying community dynamics.Les communautés végétales constituent des systèmes complexes au sein desquels de nombreuses espèces, pouvant présenter une large variété de traits fonctionnels, interagissent entre elles et avec leur environnement. En raison de la quantité et de la diversité de ces interactions les mécanismes qui gouvernent les dynamiques des ces communautés sont encore mal connus. Les approches basées sur la modélisation permettent de relier de manière mécaniste les processus gouvernant les dynamiques des individus ou des populations aux dynamiques des communautés qu'ils forment. L'objectif de cette thèse était de développer de telles approches et de les mettre en oeuvre pour étudier les mécanismes sous-jacents aux dynamiques des communautés.Nous avons ainsi développés deux approches de modélisation. La première s'appuie sur un cadre de modélisation stochastique permettant de relier les dynamiques de populations aux dynamiques des communautés en tenant compte des interactions intra- et interspécifiques et de l'impact des variations environnementale et démographique. Cette approche peut-être aisément appliquée à des systèmes réels et permet de caractériser les populations végétales à l'aide d'un petit nombre de paramètres démographiques. Cependant nos travaux suggèrent qu'il n'existe pas de relation simple entre ces paramètres et les traits fonctionnels des espèces, qui gouvernent pourtant leur réponse aux facteurs externes. La seconde approche a été développée pour dépasser cette limite et s'appuie sur le modèle individu-centré Nemossos qui représente de manière explicite le lien entre le fonctionnement des individus et les dynamiques de la communauté qu'ils forment. Afin d'assurer un grand potentiel d'application à Nemossos, nous avons apportés une grande attention au compromis entre réalisme et coût de paramétrisation. Nemossos a ainsi pu être entièrement paramétré à partir de valeur de traits issues de la littérature , son réalisme a été démontré, et il a été utilisé pour mener des expériences de simulations numériques sur l'importance de la variabilité temporelle des conditions environnementales pour la coexistence d'espèces fonctionnellement différentes. La complémentarité des deux approches nous a permis de proposer des éléments de réponse à divers questions fondamentales de l'écologie des communautés incluant le rôle de la compétition dans les dynamiques des communautés, l'effet du filtrage environnementale sur leur composition fonctionnel ou encore les mécanismes favorisant la coexistence des espèces végétales. Ici ces approches ont été utilisées séparément mais leur couplage peut offrir des perspectives intéressantes telles que l'étude du lien entre le fonctionnement des plantes et les dynamiques des populations. Par ailleurs chacune des approches peut être utilisée dans une grande variété d'expériences de simulation susceptible d'améliorer notre compréhension des mécanismes gouvernant les communautés végétales

Fault-recovery and Coherence in Internet of Things Choreographies

International audienceFacilitating the creation of Internet of Things (IoT) applications is a major concern to increase its development. D-LITe, our previous work, is a framework for that purpose. In D-LITe, Objects are considered as part of a whole application. They offer a REST web service that describes Object capabilities, receives the logic to be executed, and interacts with other stakeholders. Then, the complete application is seen as a choreography dynamically deployed on various objects. But the main issue of choreographies is the loss of coherence. Because of their unreliability, some networks used in IoT may introduce de-synchronization between Objects, leading to errors and failures. In this paper, we propose a solution to re-introduce coherence in the application, in order to keep the advantages of choreography while dealing with this main issue. An overlay of logical check-points at the application layer defines links between the coherent states of a set of objects and triggers re-synchronization messages. Correcting statements are thus spread through the network, which enables fault recovery in Choreographies. This paper ends with a comparison between the checking cost and the reliability improvement

Hierarchical QOS-aware Routing in Multi-tier Multimedia Wireless Sensor Networks

International audienceThe Wireless Multimedia Sensor Networks (WMSN) are a particular case of Wireless Sensors Networks (WSN) as they present a lower density, a limited mobility, require more important resources and need QoS control to transport the multimedia streams. In this paper, we propose, starting from a reference architecture of WMSN, a first approach for hierarchical self-organizing routing ensuring a certain level of QoS

SALT: a Simple Application Logic description using Transducers for Internet of Things

International audienceAs the Internet of Things (IoT) grows in interest from both research and industrial parts, the lack of standard solutions to quickly and easily build and install IoT applications becomes a topic of high interest. In this paper, we introduce a language called SALT (Simple Application Logic description using Transducers) that allows describing and deploying the distributed logic needed in order to fulfil a complete desired application. This language aims at giving extended functionalities by filling the gap between the logical capabilities offered by services orchestration and the closeness efficiency of services choreography. SALT is interpreted by a virtual machine running on devices that introduces an abstraction layer in order to simplify access to hardware capabilities. SALT implements several mechanisms to comply with organisation issues presented in the Services Oriented Computing realm dealing with Services interactions, adapted to the specific constraints of the IoT. This work details SALT's concepts, formalism and implementation

Predicting stochastic community dynamics in grasslands under the assumption of competitive symmetry

International audienceCommunity dynamics is influenced by multiple ecological processes such as environmental spatiotemporal variation, competition between individuals and demographic stochasticity. Quantifying the respective influence of these various processes and making predictions on community dynamics require the use of a dynamical framework encompassing these various components. We here demonstrate how to adapt the framework of stochastic community dynamics to the peculiarities of herbaceous communities, by using a short temporal resolution adapted to the time scale of competition between herbaceous plants, and by taking into account the seasonal drops in plant aerial biomass following winter, harvesting or consumption by herbivores. We develop a hybrid inference method for this novel modelling framework that both uses numerical simulations and likelihood computations. Applying this methodology to empirical data from the Jena biodiversity experiment, we find that environmental stochasticity has a larger effect on community dynamics than demographic stochasticity, and that both effects are generally smaller than observation errors at the plot scale. We further evidence that plant intrinsic growth rates and carrying capacities are moderately predictable from plant vegetative height, specific leaf area and leaf dry matter content. We do not find any trade-off between demographical components, since species with larger intrinsic growth rates tend to also have lower demographic and environmental variances. Finally, we find that our model is able to make relatively good predictions of multi-specific community dynamics based on the assumption of competitive symmetr

Intelligent Antenna Selection Decision in IEEE 802.15.4 Wireless Sensor Networks: An Experimental Analysis

International audienceThe goal of this paper is to study the feasibility of making intelligent antenna selection decision in IEEE 802.15.4 Wireless Sensor Networks (WSNs). This study provides us the basis to design and implement software defined intelligent antenna switching capability to wireless sensor nodes based on Received Signal Strength Indicator (RSSI) link quality metric. First, we discuss the results of our newly designed radio module (Inverted-F Antenna) for 2.4 GHz bandwidth (WSNs). Second, we propose an intelligent antenna selection strategy to exploit antenna diversity. Third, we propose the prototype of our diversity antenna for the TelosB mote and the intelligent switch design. Finally, we compare the performance of the built-in TelosB antenna with our proposed external antenna in both laboratory and realistic environments. Experimental results confirm the gain of 6 to 10 dB of the proposed radio module over the built-in radio module of the TelosB motes