Trace-based Collaborative Learning System

The users of any educational software may leave traces which concern all their activities. In collaborative learning context, these traces are very voluminous and very heterogeneous. They are the results of various interactions between the actors themselves, and between the actors and the system. Hence, first, they must be collected and filtered. Then, these traces must be analyzed to help or support these actors (the tutor in his task of monitoring learners and the teacher-author in his task of creating educational courses). It is this context that defines our research work, which is focused on implementing a collaborative learning system based on traces called SYCATA (SYstème pour la Collecte et l’Analyse des Traces d’Apprentissage collaboratif). SYCATA collects all traces of actors’ activities (especially learners) and groups them into five categories. It offers a multitude of forms (graphical, numerical or mixed) to show these traces to the tutors and the authors. Some traces may be viewed by learners to promote their pedagogical activities and raise their awareness. SYCATA was implemented and experimented with a sample of university students where good results have been obtained

Experimental study of two-phase flow structure and pressure drop across a sudden contraction in horizontal pipe

Two-phase flow, particularly; gas-liquid flow is widely encountered in industrial applications like boilers, condensers, evaporators and reactors. These systems often exhibit complex geometry consisting on singularities such as expansions, contractions, orifices, bends etc. The presence of geometrical singularities in pipes may affect significantly the behavior of two-phase flow and subsequently the resulting pressure drop. Therefore, it is an important subject of investigation in particular when the application concerns design, safety and economical operations. This study investigates the pressure change and flow pattern subject to the influence of a sudden contraction. The pressures through sudden contraction in horizontal circular pipes have been measured with a capacitive differential pressure transducer, using air and water as the working fluids. The pressure drop is determined by extrapolating the pressure profiles upstream and downstream of the contraction. The larger and smaller tube diameters are 40 mm and 30 mm, respectively, with an area contraction ratio >\u1d70e= 0.567 . The ranges of the gas and liquid superficial velocity were 0.54 to 5.5 m/s and 0.011 up to 0.24 m/s respectively. It is noted that the sudden change in cross-section have a significant influence on the downstream phase distribution of the air-water flow. In addition, close to the sudden contraction, a significant pressure drop occurs for single phase flow (water). While, for two-phase flow cases, a local pressure minimum was not detectable, the vena contracta phenomenon may not occur at all especially at low flow rates

Dynamic simulation of preformed aqueous foam stability for enhanced oil recovery application

Aqueous foam is a two-phase system consisting of a continuous liquid phase and a dispersed gas phase. Foams are widely used in a variety of industrial operations, such as the enhanced recovery of hydrocarbons. Because of their unique properties, they can solve a variety of reservoir heterogeneity problems, including early gas breakthrough, channeling, and even viscous fingering. A variety of phenomena affect the stability of foams during flow, for example, the drainage process, gas diffusion, and bubble coalescence. In this research, we used the level-set method to simulate foam stability in various aspects, such as factors affecting foam drainage and coalescence phenomena. According to the simulation results, the foam's lifetime is greatly impacted by the phenomena of drainage and coalescence. Moreover, its stability is strongly influenced by salt as well as the type of gas used to generate it

CoZi: basic Coding for better Bandwidth Utilization in ZigBee Sensor Networks

International audienceThis paper describes CoZi, a new packet scheduling mechanism for large scale ZigBee networks. CoZi aims at enhancing the reliability of the data delivery and the bandwidth utilization of the network. Based on simple network coding, instead of the classic packet forwarding, our algorithm takes advantage of the shared nature of the wireless medium as well as the cluster-tree topology of IEEE 802.15.4 networks to increase the global throughput and to reduce transmissions in end-to-end and dissemination-based communications

Reliable Network Coding for ZigBee Wireless Sensor Networks

International audienceIt has been analytically and empirically proved that Network Coding can significantly enhance wireless communications in terms of achievable throughput, data delivery and delay. While research in Network Coding has mainly ad dressed the problem of coding efficiency, buffer optimization and queuing, little attention has been paid to what we define as coding reliability, i.e., the ability for nodes to encode packets efficiently enough, so that a maximum number of its destinations can extract innovative data whatever the medium conditions can be. In this work, we investigate this concept in Wire less Sensor Networks (WSN) then we present Re-CoZi, a pack et transport mechanism which enables robust XOR Coding for WSN using echo-feedback packet reception and decoding acknowledgement. Our performance analysis shows that Re CoZi keeps the added value of NC in terms of bandwidth utilization and delay, while providing a more reliable coding

Network Coding for Event-Centric Wireless Sensor Networks

International audienceWe propose Wireless Sensor Coding (WSC) an eventcentric data-dissemination scheme for Wireless Sensor Networks (WSN). WSC is based on a distributed network coding scheme. In this solution, nodes do not only forward packets, but also perform linear random information coding in order to increase the throughput of the network, to reduce the number of transmissions and the end-to-end delay. These improvements involve a reduction of the energy consumption, which is one of the key-issues in WSN architecture design

ZInC: Index-Coding for Many-to-One Communications in ZigBee Sensor Networks

Abstract—The main goal in wireless sensor networking remains the reduction of the network lifecycle and the enhancement of its reliability, keeping decent performances in terms of throughput and latency. Given the increasing interest of the research community on wireless network coding (NC), we think such challenges can be tackled using its innovative concepts, especially in the case of many-to-one communications where network coding has shown promising theoretical results. Yet, without a thoughtful adaptation to WSNs, the benefits of NC for sensor networking prove to be too “greedy ” and impractical. In this paper, we propose index-coding, a simple and effective packet coding scheme that enhances significantly many-to-one communications in ZigBee sensor networks. Index-coding uses smart bit-shifting operations in order to encode short messages from a set of sensors to a sink using fewer transmissions. Our implementation in a real ZigBee testbed shows substantial enhancement of network performances and resiliency

When network coding improves the performances of clustered wireless networks

International audienceThis paper introduces a network coding scheme that significantly increases the performances of clustering algorithms in wireless multi-hop networks. Knowing the promising capabilities of network coding over broadcast mediums, we propose a simple and non-invasive packet scheduling mechanism based on proactive code selection and overheard messages to optimize intra and inter-cluster communications. Our solution uses bitwise XOR operations at the packet level to combine several messages in one transmission. Simulations show an important gain in the network reliability, and a major enhancement of the throughput without any substantial computation or network overhead

Stability analysis of inclined stratified two-phase gas–liquid flow

The present investigation involves the modeling of gas–liquid interface in a two-phase stratified flow through a horizontal or nearly-horizontal circular duct. The most complete and fundamental model used for these calculations is known as the one-dimensional two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links both phases with six conservation equations. The mass and momentum balance equations are written in dimensionless form. The dimensionless mass and momentum balance equations are combined with the method of characteristics and an explicit method to simulate the flow. At first, the linear stability of the flow is investigated by disturbing the liquid flow with a small perturbation. An improved version of the one-dimensional twofluid model for horizontal flows is developed as a set of non-linear hyperbolic governing equations. The importance of this research lies in obtaining a model that accounts for the effects of flow and geometrical conditions (such as liquid viscosity, surface tension). It is shown that, for positive values of the slope angle (upward inclination), the slug flow becomes more probable, whereas negative values of the slope angle (downward inclination) induce a more stable stratified flow.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe