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Accurate experimental characterization of longitudinal vortices induced by rectangular winglets is necessary to develop and validate numerical models that can predict these flows. For this aim, an experimental investigation is conducted to examine the characteristics of longitudinal vortices generated downstream rectangular winglets in fully developed turbulent channel flow. A row of rectangular winglet pairs is implemented in a parallel plate flow. Stereoscopic Particle Image Velocimetry (SPIV) is used to harvest three-dimensional (3D) instantaneous velocity fields for a Re = 4400 based on the channel’s hydraulic diameter and mean flow velocity. 3D velocity components, velocity streamlines, topologies of Γ2 function and normalized turbulent kinetic energy downstream the winglets are analyzed. It is shown that the flow properties are disturbed, and a main vortex pair is generated in addition to induced vortices downstream the rectangular winglets. Moreover, this work provides an SPIV benchmark of the complex flow developing downstream rectangular winglet pairs, where this configuration has been widley studied using numerical simulations.

Many efforts have been deployed by the IR community to extend free-text query processing toward semi-structured XML search. Most methods rely on the concept of Lowest Comment Ancestor (LCA) between two or multiple structural nodes to identify the most specific XML elements containing query keywords posted by the user. Yet, few of the existing approaches consider XML semantics, and the methods that process semantics generally rely on computationally expensive word sense disambiguation (WSD) techniques, or apply semantic analysis in one stage only: performing query relaxation/refinement over the bag of words retrieval model, to reduce processing time. In this paper, we describe the building blocks of a new approach for XML keyword search aiming to solve the limitations mentioned above. Our solution first transforms the XML document collection (offline) and the keyword query (on-the-fly) into meaningful semantic representations using context-based and global disambiguation methods, specially designed to allow almost linear computation efficiency. Consequently, the semantically augmented XML data tree is processed for structural node clustering, based on semantic query concepts (i.e., key-concepts), in order to identify and rank candidate answer sub-trees containing related occurrences of query key-concepts. Preliminary experiments highlight the quality and potential of our approach.

International audience; Phase Change Materials (PCM) have been a emerging research topic for the last few years. However, the lack of detailed and precise information regarding their thermophysical properties is a major concern for researchers. The current paper presents a simple method to determine the specific heat (Cp), thermal conductivity (K) and melting temperature (Tm) of a PCM using a novel low cost device. Compared to the conventional existing methods such as Differential Scanning Calorimetry (DSC), T-history, panel test and simple thermal analysis, this new method grants the following features: simplicity and ease of manufacturing and the ability to measure the thermophysical properties of heterogeneous PCMs samples without a reference material. Using this novel device, the thermophysical properties of the sodium sulfate decahydrate were measured and good agreement is obtained with values collected from the open literature using other devices.

International audience; The study of recommender systems is essential nowadays due to its great effect on businesses and customer satisfaction. Different active learning strategies were previously developed to gain ratings from the users on specific items, and this enables the system to have more information and consequently make more accurate recommendations. In previous studies, these strategies were evaluated using a different selection of metrics in each work, and the experimentations were done on different datasets. In this paper, we solve these weaknesses by comparing the main ten non-personalized strategies on a fair ground, by simulating them against two datasets and using seven of the mostly agreed upon metrics. This gives more trust and less biased results when comparing their performances. Also, the analysis of the computation time and the elicitation efficiency is added.

International audience; Recommender systems have a better performance whenever they have more information about the users. When little to no information is available for a certain user, the system fails to provide them with accurate recommendations, and this is referred to as the cold-start problem. To solve this issue, non- personalized and personalized active learning strategies were proposed, with an aim to obtain some ratings from the new user on specific items. In this paper, we tackle the non-personalized category, we compare the strategies that were previously suggested in the literature, and we propose a new strategy that combines some selected previous strategies. We use the public MovieLens dataset in the experimentations and we use MAE and RMSE to compare the strategies. The results show that our strategy performs better than the individual strategies previously used.

International audience; In this paper, a reconfigurable patch antenna design operating at 868MHz for Low Power Wide Area Network (LoRa), 1.58 GHz for Global Positioning System (GPS) and 2.4 GHz for Bluetooth is presented. The design is reconfigurable thanks to the integration of a digitally tunable capacitor (DTC). The DTC capacitance changes according to a 5 bits' sequence command. A microcontroller is used to assign the required sequence, and thus leading to frequency reconfiguration. The antenna is a circular patch with a gain that varies from 0.2 dB to 6 dB based on the desired frequency of operation and the reconfiguration state. The antenna is designed for internet of things (IoT) applications.

International audience; Passive methods are widely used for flow control in engineering processes for heat and mass transfer enhancement. Using flexible vortex generators (FVGs) in such applications in order to destabilize the flow can be thought to achieve higher performances taking advantage of the fluid-structure interaction. In this paper, we discuss the assessment of getting self-sustained large oscillation amplitudes of multiple FVGs from an upstream confined laminar flow. The FVGs are located on the opposite channel walls in alternated positions, separated by a distance equal to their span and inclined in the upstream direction with an angle of 30° with respect to the wall. Five cases are studied which differ by the number of alternating FVGs in the system and investigations are also performed adding two co-planar FVGs upstream. The Reynolds number is held constant with a value of 2000 (based on the hydraulic diameter) for all the cases. The effect of increasing the degree of freedom of the system, on creating a large displacement flapping motion is numerically investigated. The results show that a minimum of three alternating FVGs is needed to produce a self-sustained and periodic flow instability, leading to large FVG displacement when the co-planar FVGs are not present. The introduction of upstream co-planar FVGs destabilizes the flow by producing vortices which act as periodic forces on the downstream FVGs. In this case, large displacement amplitudes are thus observed with two alternating FVGs added downstream. A phenomenon of inverted drafting is observed in all the cases: upstream FVGs display smaller drag force values than the downstream ones. Since the downstream FVGs oscillate in resonance with the incoming flow, motion amplitudes become higher. Moreover, it has been observed that for all the configurations studied here, the FVGs located at the same wall location oscillate in phase with each others and out-of-phase with the ones located on the opposite channel wall.

This paper aims to assess the impact of the envelope airtightness on both heating needs and airflow patterns for the case of a single-detached dwelling as function of the ventilation system. An original numerical approach based on the energy simulation tool TRNSYS coupled to the multi-zone airflow and contaminant transport model COMIS was used to compare the performance of four mechanical ventilation strategies. The impacts of the envelope leakage location (facades and/or ceiling), the zone configuration (one- or multi-zone model), the climatic and wind exposure conditions (exposed or surrounded by obstructions) were also investigated. The results show a significant increase of the heating needs when the air permeability at 4 Pa is increased depending on the climatic conditions. Furthermore, the desired airflow pattern, and hence the dispersion of pollutants from main rooms to service rooms can be significantly disturbed especially in the case of humidity-sensitive ventilation system.

Several vortex generator shapes are used to increase heat and mass transfer in open and internal flows. Here we report a three-dimensional numerical study investigating the effects of longitudinal and transverse vortices on the heat and mass transfer mechanisms generated by rows of trapezoidal vortex generators. The turbulent macrostructures of these streamwise vortices appear greatly to enhance radial convective transfer. Due to Kelvin-Helmholtz instability, the shear layer shed from the tab's edge becomes unstable and generates periodic transverse vortices that enhance fluid mixing and heat transfer. A global performance analysis of the high-efficiency vortex (HEV) heat exchanger designed to exploit these embedded vortices, shows that the HEV is very competitive with other multifunctional heat exchangers/reactors, especially due to its very low energy consumption. (C) 2010 Elsevier Ltd. All rights reserved.

Crowdsourcing mobile applications are of increasing importance due to their suitability in providing personalized and better matching replies. The competitive edge of crowdsourcing is twofold; the requestors can achieve better and/or cheaper responses while the crowd contributors can achieve extra money by utilizing their free time or resources. Crowdsourcing location-based services inherit the querying mechanism from their legacy predecessors and this is where the threat lies. In this paper, we are going to show that none of the advanced privacy notions found in the literature except forK-anonymity is suitable for crowdsourced location-based services. In addition, we are going to prove mathematically, using an attack we developed, thatK-anonymity does not satisfy the privacy level needed by such services. To respond to this emerging threat, we will propose a new concept, totally different from existing resource consuming privacy notions, to handle user privacy using Mobile Cloud Computing.

International audience; The behavioral service composition problem arises when no available service can achieve a target behavior. The composition problem consists in building a special service, an orchestrator, which schedules the actions of the services to produce a behavior equivalent to the target one. In this paper, services are modeled as nondeterministic transition systems and the behavior of the composition realizes the behavior of the target. We propose an algorithm that avoids the full computation of the product of services, and instead constructs the orchestrator incrementally. Unlike most algorithms where the whole state space, which is exponential in the number of services, is visited, the proposed algorithm can find a solution by visiting only the pertinent portion of the state space. We also show that this on-the-fly behavior can be paired with a heuristic to speed up the synthesis.

International audience; The influence of the wake vortex arising behind a perforated tab on the mixing processin heat exchangers and chemical reactors is analyzed. The preliminary step of this study, i.e., investigation of the turbulent field generated by a single perforated tab, is presented here. For this aim, laser Doppler velocimetry measurements are conducted downstream from a perforated trapezoidal vortex generator placed in a wind tunnel. It is shown that two shear layers are generated by the tab. The first shear layer is located at the upper edge of the tab, and the other is ejected from the perforation edges. These shear layers are characterized by high turbulent kinetic energy levels, which are profitable for meso-mixing enhancement. Finally, a spectral study shows that the turbulent macro-scale is nearly the same for typical locations in the shear layers shed from the taband perforation edges.

In the process industry, vortex generators are being increasingly incorporated in modern multifunctional heat exchangers/reactors to enhance heat and mass transfer and thus increase energy efficiency. Longitudinal and transverse pressure-driven vortices and shear-instability-driven flow structures generated by flow separation behind the vortex generators play a crucial role in convective transport phenomena. The purpose of this work is to demonstrate experimentally the effects of hydrodynamics on the transfer processes accompanying such flows. The high-efficiency vortex (HEV) is an innovative static mixer and a low energy consumption heat exchanger designed to exploit these types of vortices. Heat transfer results obtained in turbulent flow with embedded vorticity in this multifunctional heat exchanger are compared with numerical results in the literature. Both numerical and experimental results confirm the high energy efficiency of the HEV static mixer flow. (C) 2012 Elsevier Ltd. All rights reserved.