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Petit J.,University Paris - Sud | Montay G.,CNRS Risk Management Science and Technology | Francois M.,CNRS Risk Management Science and Technology
International Journal of Solids and Structures | Year: 2014

Localization that occurs at the end of the tensile test of a ductile 316L stainless steel has been followed in detail by in-plane Electronic Speckle Pattern Interferometry (ESPI). A global description of the whole strain-rate field with an analytical function and physical descriptors such as band width, band inclination and maximum strain rate is proposed. The description with two straight bands of constant amplitude along the width of the specimens is valid from the beginning of the diffuse necking to the fracture of the specimens. It allows distinguishing between two localization scenarii which occur for specimens with a different width to thickness ratio, one with a fracture inclined along the width and the other with a fracture inclined in the thickness. For the former, the two bands keep a constant angle while for the latter, the two bands rotate progressively until they become perpendicular to the tensile direction. The bandwidth can be defined and monitored during the whole necking evolution. © 2013 Elsevier Ltd. All rights reserved.

Ahmed A.,University for Information Science and Technology | Boulahia L.M.,CNRS Risk Management Science and Technology | Gaiti D.,CNRS Risk Management Science and Technology
IEEE Communications Surveys and Tutorials | Year: 2014

Wireless networks are passing through a transition phase for the past few years now and this transition is giving a way towards the convergence of all IP-based networks to form the Next Generation Networks (NGNs). With the proliferation of these networks in daily life, users' needs are also increasing and service operators are offering different services to satisfy their customers for a better grade of service and an elevated quality of experience (QoE). However, a single operator cannot fulfill the huge demands of the users especially, if a user is nomadic. In nomadism, a user traverses number of available networks that might contain cellular or wireless data networks, usually known as heterogeneous wireless networks. These networks offer various services from email to live video streaming depending upon their capacity and nature. During this traversing procedure, a user switches among different networks to satisfy his/her needs in terms of quality of service. This process is commonly known as a vertical handover or handoff (VHO) due to the involvement of heterogeneous wireless networks in it. An extensive work has been carried out in this field in order to fulfill user demands for better QoS and QoE. In this paper, we give a detailed state-of-the-art of these existing vertical handover decision mechanisms that aim at providing ubiquitous connectivity to the mobile users. We have categorized these vertical handover measurement and decision schemes on the basis of their employed techniques and parameters. Also, we present a comprehensive summary of their advantages and drawbacks. This paper gives its readers an overview of the active research initiatives in the area of handover decision making process in heterogeneous wireless networks and identifies the challenges behind the seamless services provisioning during mobility. © 2014 IEEE.

Ullah I.,CNRS Risk Management Science and Technology | Doyen G.,CNRS Risk Management Science and Technology | Bonnet G.,University of Caen Lower Normandy | Gaiti D.,CNRS Risk Management Science and Technology
IEEE Communications Surveys and Tutorials | Year: 2012

In terms of scalability, cost and ease of deployment, the Peer-to-Peer (P2P) approach has emerged as a promising solution for video streaming applications. Its architecture enables end-hosts, called peers, to relay the video stream to each other. P2P systems are in fact networks of users who control peers. Thus, user behavior is crucial to the performance of these systems because it directly impacts the streaming flow. To understand user behavior, several measurement studies have been carried out over different video streaming systems. Each measurement analyzes a particular system focusing on specific metrics and presents insights. However, a single study based on a particular system and specific metrics is not sufficient to provide a complete model of user behavior considering all of its components and the impact of external factors on them. In this paper, we propose a comparison and a synthesis of these measurements. First of all, we review video streaming architectures, followed by a survey on the user behavior measurements in these architectures. Then, we gather insights revealed in these measurements and compare them for consensual and contrasting points. Finally, we extract components of user behavior, their external impacting factors and relationships among them. We also point out those aspects of user behavior which require further investigations. © 2012 IEEE.

Honeine P.,CNRS Risk Management Science and Technology | Richard C.,University of Nice Sophia Antipolis
IEEE Signal Processing Magazine | Year: 2011

Kernel machines have gained considerable popularity during the last 15 years, making a breakthrough in nonlinear signal processing and machine learning, thanks to extraordinary advances. This increased interest is undoubtedly driven by the practical goal of being able to easily develop efficient nonlinear algorithms. The key principle behind this, known as the kernel trick, exploits the fact that a great number of data-processing techniques do not explicitly depend on the data itself but rather on a similarity measure between them, i.e., an inner product. © 2006 IEEE.

Duhamel C.,CNRS Laboratory of Informatics, Modeling and Optimization of Systems | Lacomme P.,CNRS Laboratory of Informatics, Modeling and Optimization of Systems | Prodhon C.,CNRS Risk Management Science and Technology
Engineering Applications of Artificial Intelligence | Year: 2012

Routing Problems have been deeply studied over the last decades. Split procedures have proved their efficiency for those problems, especially within global optimization frameworks. The purpose is to build a feasible routing solution by splitting a giant tour into trips. This is done by computing a shortest path on an auxiliary graph built from the giant tour. One of the latest advances consists in handling extra resource constraints through the generation of labels on the nodes of the auxiliary graph. Lately, the development of a new generic split family based on a Depth First Search (DFS) approach during label generation has highlighted the efficiency of this new method for the routing problems, through extensive numerical evaluations on the location-routing problem. In this paper, we present a hybrid Evolutionary Local Search (hybrid ELS) for non-homogeneous fleet Vehicle Routing Problems (VRP) based on the application of split strategies. Experiments show our method is able to handle all known benchmarks, from Vehicle Fleet Mix Problems to Heterogeneous Fleet VRP (HVRP). We also propose a set of new realistic HVRP instances from 50 to more than 250 nodes coming from French counties. It relies on real distances in kilometers between towns. Since many classical HVRP instance sets are solved to optimality, this new set of instances could allow a fair comparative study of methods. The DFS split strategy shows its efficiency and attests the fact that it can be a promising line of research for routing problems including numerous additional constraints. © 2011 Elsevier Ltd. All rights reserved.

Panicaud B.,CNRS Risk Management Science and Technology
International Journal of Theoretical Physics | Year: 2011

The multivectorial algebras present yet both an academic and a technological interest. Difficulties can occur for their use. Indeed, in all applications care is taken to distinguish between polar and axial vectors and between scalars and pseudo scalars. Then a total of eight elements are often considered even if they are not given the correct name of multivectors. Eventually because of their simplicity, only the vectorial algebra or the quaternions algebra are explicitly used for physical applications. Nevertheless, it should be more convenient to use directly more complex algebras in order to have a wider range of application. The aim of this paper is to inquire into one particular Clifford algebra which could solve this problem. The present study is both didactic concerning its construction and pragmatic because of the introduced applications. The construction method is not an original one. But this latter allows to build up the associated real algebra as well as a peculiar formalism that enables a formal analogy with the classical vectorial algebra. Finally several fields of the theoretical physics will be described thanks to this algebra, as well as a more applied case in general relativity emphasizing simultaneously its relative validity in this particular domain and the easiness of modeling some physical problems. © 2011 Springer Science+Business Media, LLC.

Hamdi-Dhaoui K.,CNRS Risk Management Science and Technology | Labadie N.,CNRS Risk Management Science and Technology | Yalaoui A.,CNRS Risk Management Science and Technology
RAIRO - Operations Research | Year: 2012

The two-dimensional bin packing problem is a well-known problem for which several exact and approximation methods were proposed. In real life applications, such as in Hazardous Material transportation, transported items may be partially incompatible, and have to be separated by a safety distance. This complication has not yet been considered in the literature. This paper introduces this extension called the two-dimensional bin packing problem with partial conflicts (2BPPC) which is a 2BP with distance constraints between given items to respect, if they are packed within a same bin. The problem is NP-hard since it generalizes the BP, already NP-hard. This study presents a mathematical model, two heuristics and a multi-start genetic algorithm for this new problem. © 2012 EDP Sciences, ROADEF, SMAI.

Barchiesi D.,CNRS Risk Management Science and Technology
Optics Communications | Year: 2013

The surface plasmon resonance (SPR) is known since the late 1950s. Its understanding was popularized by analytical models, in simple cases such as metallic plane plates between two dielectric media. The optimization of such structure for SPR biosensor applications is traditionally based on the minimization of the reflectance. Nevertheless this approach suffers from instabilities that require the limitation of the domain of search. An alternative formulation using the scattering matrix is proposed to improve the efficiency of optimization of this setup. The proposed model is mathematically rigorous and is coherent with the description of resonances in other fields of physics. The results of optimization and sensitivity analysis are discussed. © 2012 Elsevier B.V. All rights reserved.

Fillatre L.,CNRS Risk Management Science and Technology
IEEE Transactions on Signal Processing | Year: 2012

This paper deals with the detection of hidden bits in the Least Significant Bit (LSB) plane of a natural image. The mean level and the covariance matrix of the image, considered as a quantized Gaussian random matrix, are unknown. An adaptive statistical test is designed such that its probability distribution is always independent of the unknown image parameters, while ensuring a high probability of hidden bits detection. This test is based on the likelihood ratio test except that the unknown parameters are replaced by estimates based on a local linear regression model. It is shown that this test maximizes the probability of detection as the image size becomes arbitrarily large and the quantization step vanishes. This provides an asymptotic upper-bound for the detection of hidden bits based on the LSB replacement mechanism. Numerical results on real natural images show the relevance of the method and the sharpness of the asymptotic expression for the probability of detection. © 2011 IEEE.

Jia K.,CNRS Risk Management Science and Technology | Bijeon J.L.,CNRS Risk Management Science and Technology | Adam P.M.,CNRS Risk Management Science and Technology | Ionescu R.E.,CNRS Risk Management Science and Technology
Analytical Chemistry | Year: 2012

Herein are reported two new protocols to obtain different zones of localized surface plasmon resonance (LSPR) gold nanostructures on single glass substrate by using a vacuum evaporation technique followed by a high-temperature annealing (550 °C). The thickness of the gold film, considered as the essential parameter to determine specific LSPR properties, is successfully modulated. In the first protocol, a metal mask is integrated onto the glass substrate during vacuum evaporation to vary the gold film thickness by a "shadowing effect", while in the second protocol several evaporation cycles (up to four cycles) at predefined areas onto the single substrate are performed. The resulting gold-modified samples are characterized using a transmission UV-vis extinction optical setup and scanning electron microscopy (SEM). The size distribution histograms of nanoparticles are also acquired. By employing the first protocol, thanks to the presence of different zones of gold nanoparticles on a single substrate, optimized LSPR responses to different (bio)functionalization zones are rapidly screened. Independently, the second protocol exhibited an excellent correlation between the nominative evaporated gold film thickness, gold nanoparticle sizes, and plasmonic properties (resonant wavelength and peak amplitude). Such substrates are further used in the construction of LSPR immunosensors for the detection of atrazine herbicide. © 2012 American Chemical Society.

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