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Now showing items 17 - 32 of 40

  • In situ heating transmission electron microscopy observation of nanoeutectic lamellar structure in Sn-Ag-Cu alloy on Au under-bump metallization.

    Jong-Hyun Seo   Sang-Won Yoon   Kyou-Hyun Kim   Hye-jung Chang   Kon-Bae Lee   Tae-Yeon Seong   Eric Fleury   Jae-Pyoung Ahn  

    We investigated the microstructural evolution of Sn(96.4)Ag(2.8)Cu(0.8) solder through in situ heating transmission electron microscopy observations. As-soldered bump consisted of seven layers, containing the nanoeutectic lamella structure of AuSn and Au₅Sn phases, and the polygonal grains of AuSn₂ and AuSn₄, on Au-plated Cu bond pads. Here, we found that there are two nanoeutectic lamellar layers with lamella spacing of 40 and 250 nm. By in situ heating above 140°C, the nanoeutectic lamella of AuSn and Au₅Sn was decomposed with structural degradation by sphering and coarsening processes of the lamellar interface. At the third layer neighboring to the lamella layer, on the other hand, Au₅Sn particles with a zig-zag shape in AuSn matrix became spherical and were finally dissipated in order to minimize the interface energy between two phases. In the other layers except both lamella layers, polycrystal grains of AuSn₂ and AuSn₄ grew by normal grain growth during in situ heating. The high interface energy of nanoeutectic lamella and polygonal nanograins, which are formed by rapid solidification, acted as a principal driving force on the microstructural change during the in situ heating.
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  • Worldsens: Development and Prototyping Tools for Application Specific Wireless Sensors Networks

    Antoine Fraboulet   Guillaume Chelius   Eric Fleury  

    In this paper we present Worldsens, an integrated environment for development and rapid prototyping of wireless sensor network applications. Our environment relies on software simulation to help the designer during the whole development process. The refinement is done starting from the high level design choices down to the target code implementation, debug and performance analysis. In the early stages of the design, high level parameters, like for example the node sleep and activity periods, can be tuned using WS-Net, an event driven wireless network simulator. WSNet uses models for applications, protocols and radio medium communication with a parameterized accuracy. The second step of the sensor network application design takes place after the hardware implementation choices. This second step relies on the WSim cycle accurate hardware platform simulator. WSim is used to debug the application using the real target binary code. Precise performance evaluation, including real-time analysis at the interrupt level, are made possible at this low simulation level. WSim can be connected to WSNet, in place of the application and protocol models used during the high level simulation to achieve a full distributed application simulation. WSNet and WSNet+WSim allow a continuous refinement from high level estimations down to low level real-time validation. We illustrate the complete application design process using a real life demonstrator that implements a hello protocol for dynamic neighborhood discovery in a wireless sensor network environment.
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  • A Distributed Policy Scheduling for Wireless Sensor Networks

    Yu Chen   Eric Fleury  

    We aim to save energy by scheduling periodic sensors' duty cycles. Different from existing works, we integrate two important tasks, collision avoidance and duty cycling, into one scheduling of sensors' activities. Our scheme consists of two parts: a coloring scheme that assigns a "color" to each sensor and a color scheduling scheme that associates each color with a schedule. Each sensor switches between sleep and active modes according to the schedule associated with its color. We propose a coloring definition. Theoretical analyses and simulation results show that, if this coloring is used by collision avoidance schemes such as TDMA or CDMA, connectivity can be guaranteed by using much less colors than traditional colorings. Theoretical analyses and simulation evaluations are presented for our scheduling. As compared to handling collision avoidance and duty cycling separately, performances can be improved by integrating these two tasks into one carefully designed schedule of sensors' activities. In particular, in duty cycled dense networks, in order to reduce packet latency and save energy, it is desirable to guarantee the communication connectivity of links only in a sparse connected subgraph.
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  • Neighbor discovery in multi-hop wireless networks: evaluation and dimensioning with interference considerations†

    Elyes Ben Hamida   Anthony Busson   Eric Fleury  

    In this paper; we study the impact of collisions and interference on a neighbor discovery process in the context of multi-hop wireless networks. We consider three models in which interference and collisions are handled in very different ways. From an ideal channel where simultaneous transmissions do not interfere; we derive an alternate channel where simultaneous transmissions are considered two-by-two under the form of collisions; to finally reach a more realistic channel where simultaneous transmissions are handled under the form of shot-noise interference. In these models; we analytically compute the link probability success between two neighbors as well as the expected number of nodes that correctly receive a Hello packet. Using this analysis; we show that if the neighbor discovery process is asymptotically equivalent in the three models; it offers very different behaviors locally in time. In particular; the scalability of the process is not the same depending on the way interference is handled. Finally; we apply our results to the dimensioning of a Hello protocol parameters. We propose a method to adapt the protocol parameters to meet application constraints on the neighbor discovery process and to minimize the protocol energy consumption.
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  • An Evaluation of the NAP Protocol for IPv6 Router Auto-configuration

    Guillaume Chelius   Eric Fleury   Bruno Sericola   Laurent Toutain   David Binet  

    This paper presents a model of the NAP protocol; dedicated to the auto-configuration of IPv6 routers. If hosts autoconfiguration is defined by IPv6; IPv6 routers still have to be manually configured. In order to succeed in new networking domains; a full auto-configuration feature must be offered. NAP offers a fully distributed solution that uses a link state OSPFv3-like approach to perform prefix collision detection and avoidance. In this paper; we present a model for NAP and analyze the average and maximum autoconfiguration delay as a function of the network size and the prefix space size.
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  • Multicasting Control and Communications on Multihop Stack-Ring OPS Networks

    Afonso Ferreira   Eric Fleury   Miltos D. Grammatikakis  

    We propose dynamic multicasting on an N = m n processor; OPS-based stack-ring topology consisting of n processor groups; with m processors each. By considering multicasting; we realize the increased network bandwidth offered by one-to-many optical communications. We assume that each processor has infinite local and network buffers and that the system performs synchronously. Assuming shortest path routing and network packet priority; we compute network throughput and latency measures as a function of the packet arrival rate. Balanced networks with m n offer higher throughput for uniform; multicast-free traffic. When the multicasting load and especially the locality of references increase; stack-ring systems with n > m offer higher throughput and reasonable latency. A high level of locality and multicasting are necessary for achieving stack-ring network scalability.
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  • Duplicate Address Detection in Wireless Ad Hoc Networks Using Wireless Nature

    Yu Chen   Eric Fleury  

    We consider duplicate address detection in wireless ad hoc networks under the assumption that addresses are unique in two hops neighborhood. Our approaches are based on the concepts of physical neighborhood views; the information of physically connected nodes; and logical neighborhood views; which are built on neighborhood information that is propagated in networks. Since neighborhood information is identified by addresses; inconsistency of these two views might be caused due to duplicate addresses. It is obvious that consistency of physical and logical views on each node’s neighborhood is necessary for a network to have unique addresses; while the sufficiency depends on the types of information contained in views of neighborhood. We investigate different definitions of neighborhood views. Our results show that the traditional neighborhood information; neighboring addresses; is not sufficient for duplication detetion; while the wireless nature of ad hoc networks provides powerful neighborhood information in detecting duplication. Key-words: duplicate address detection; wireless ad hoc networks; wireless nature in ria -0 00 70 18 5; v er si on 1 19 M ay 2 00 6 Détection de duplication d’adresse dans les réseaux ad hoc en utilisant les caractéristiques sans fil. Résumé : Pas de résumé Mots-clés : Pas de motclef in ria -0 00 70 18 5; v er si on 1 19 M ay 2 00 6 Duplicate Address Detection in Wireless Ad Hoc Networks 3
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  • On the Structure of Changes in Dynamic Contact Networks

    Vincent Neiger   Christophe Crespelle   Eric Fleury  

    We present a methodology to investigate the structure of dynamic networks in terms of concentration of changes in the network. We handle dynamic networks as series of graphs on a fixed set of nodes and consider the changes occurring between two consecutive graphs in the series. We apply our methodology to various dynamic contact networks coming from different contexts and we show that changes in these networks exhibit a non-trivial structure: they are not spread all over the network but are instead concentrated around a small fraction of nodes. We compare our observations on real-world networks to three classical dynamic network models and show that they do not capture this key property.
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  • Enhancing the high temperature plasticity of a Cu-containing austenitic stainless steel through grain boundary strengthening

    Gaurav Singh   Sung-Min Hong   Keiichiro Oh-ishi   Kazuhiro Hono   Eric Fleury   Upadrasta Ramamurty  

    Abstract The addition of 3 wt% Cu to heat-resistant SUS 304H austenitic steel enhances its high temperature mechanical properties. To further improve the properties, particularly the creep resistance and ductility at high temperatures, a post-solutionizing heat-treatment method that involves an intermediated annealing either at 700 or 800 °C after solutionizing for durations up to 180 min was employed. The purpose this heat-treatment is to precipitate planar Cr 23 C 6 at the grain boundaries, which results in the boundaries getting serrated. Detailed microstructural analyses of these ‘grain boundary engineered’ alloys was conducted and their mechanical performance, both at room temperature and at 750 °C, was evaluated. While the grain size and texture are unaffected due to the high temperature hold, the volume fraction of Ʃ3 twin boundaries was found to increase significantly. While the strength enhancement was only marginal, the ductility was found to increase significantly, especially at high temperature. A marked increase in the creep resistance was also noted, which is attributed to the reduction of the grain boundary sliding by the grain boundary serrations and the suppression of grain boundary cavitation through the optimization of the volume fraction and spacing of the Cr 23 C 6 precipitates. The special heat-treatment performed with holding time of 3 h at 700 °C resulted in the optimum combination of strength, ductility and creep resistance at high temperature.
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  • A unifying model for representing time-varying graphs

    Klaus Wehmuth   Artur Ziviani   Eric Fleury  

    Graph-based models form a fundamental aspect of data representation in Data Sciences and play a key role in modeling complex networked systems. In particular, recently there is an ever-increasing interest in modeling dynamic complex networks, i.e. networks in which the topological structure (nodes and edges) may vary over time. In this context, we propose a novel model for representing finite discrete Time-Varying Graphs (TVGs), which are typically used to model dynamic complex networked systems. We analyze the data structures built from our proposed model and demonstrate that, for most practical cases, the asymptotic memory complexity of our model is in the order of the cardinality of the set of edges. Further, we show that our proposal is an unifying model that can represent several previous (classes of) models for dynamic networks found in the recent literature, which in general are unable to represent each other. In contrast to previous models, our proposal is also able to intrinsically model cyclic (i.e. periodic) behavior in dynamic networks. These representation capabilities attest the expressive power of our proposed unifying model for TVGs. We thus believe our unifying model for TVGs is a step forward in the theoretical foundations for data analysis of complex networked systems.
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  • Documents Diplomatiques Suisses - Diplomatische Dokumente der Schweiz - Documenti Diplomatici Svizzeri. Bd. 16: 9.5. 1945-31.5. 1947by Antoine Fleury; Mauro Cerutti; Michele Coduri; Eric Flury-Dasen

    Review by: Silvia Pfeiffer-Herkenrath  

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  • Fast convergence in self-stabilizing wireless networks

    Nathalie Mitton   Eric Fleury   Isabelle Guérin Lassous   Bruno Sericola   Sébastien Tixeuil  

    The advent of large scale multi-hop wireless networks highlights problems of fault tolerance and scale in distributed systems, motivating designs that autonomously recover from transient faults and spontaneous reconfigurations. Self-stabilization provides an elegant solution for recovering from such faults. We present a complexity analysis for a family of self-stabilizing vertex coloring algorithms in the context of multi-hop wireless networks. Such "coloring" processes are used in several protocols for solving many different issues (clustering, synchronizing...). Overall, our results show that the actual stabilization time is much smaller than the upper bound provided by previous studies. Similarly, the height of the induced DAG is much lower than the linear dependency on the size of the color domain (that was previously announced). Finally, it appears that symmetry breaking tricks traditionally used to expedite stabilization are in fact harmful when used in networks that are not tightly synchronized
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  • NP-Completeness of ad hoc multicast routing problems

    Guillaume Chelius   Eric Fleury  

    In this research report; we study the algorithmic complexity of different broadcast and multicast ad hoc routing problems given a wireless medium. Key-words: ad hoc networks; multicast routing; complexity; NP-completeness NP-Complétude du routage multicast ad hoc Résumé : Dans ce rapport de recherche; nous étudions la complexité algorithmique de plusieurs problèmes de routage multicast et broadcast ad hoc étant donné un médium radio. Mots-clés : réseaux ad hoc; routage multicast; complexité; NP-complétude Ad hoc multicast routing complexity 3
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  • Topic 14 Mobile and Ubiquitous Computing

    Nuno M. Preguiça   Eric Fleury   Holger Karl   Gerd Kortuem  

    Wireless communications along with portable computers; digital assistants and sensor devices provide a pervasive base for mobile computing. However realizing truly ubiquitous mobile computing requires innovative theories; paradigms and applications in various research areas including algorithms; networking; software architectures and data management. Topic 14 covers all such aspects. This topic attracted 33 submissions showing the increasing interest in the field. From the submitted papers; 8 were accepted as full papers (24% acceptance rate). The selected papers cover various aspects of mobile and ubiquitous computing highlighting the diversity of the field and thus making up an interesting and stimulating track. Paper presentations are divided into three sessions. Two papers in the first session address consistency issues. In “Efficient and Fault-Tolerant Update Commitment for Weakly Connected Replication”; J. Barreto and P. Ferreira propose a novel epidemic weighted voting protocol for achieving eventual consistency in optimistic replication that allows multiple update candidates in an election. In “Controlling Concurrency in Mobile Computing Environments with Broadcast-based Dissemination”; J. M. Monteiro and A. Brayner present a new serializability-based protocol for ensuring data consistency and currency when data are disseminated to clients through wireless broadcast. The last paper in this session; “Integrating Mobile Devices into the Grid: Design Considerations and Evaluation” by S. Isaiadis and V. Getov; discusses implementation and performance issues for integrating mobile devices into the grid. The second session is shared with Topic 8. The two papers address aspects related to frequency utilization in wireless networking. In “New Bounds on the Competitiveness of Randomized Online Call Control in Cellular Networks”; I. Karagiannis; C. Kaklamanis and E. Papaioannou present new upper and lower bounds for the online version of the call control problem in wireless cellular networks. In “A Multiple Channel Access Protocol for Ad Hoc Wireless Networks”; K-W. Jang considers the problem of enhancing channel utilization in wireless ad hoc networks through channel exchange between neighboring nodes. In the last session; in “Personalized Access to Semantic Web Agents Using Smart Cards”; R. C. Erdur and G. Kardas argue for storing personal information on smart cards. The other two papers focus on secure networking. K. Kim; J. Hong and J. Lim present a “Fast and Secure Communication Resume Protocol” to speed up connection resume after a communication error. In “On AAA with Extended IDK in Mobile IP Networks”; H. Jeon; M. Y. Chung and H. Choo discuss how to attain fast and secure mobile IP networking by addressing problems of the hand-off process in a secure way.
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  • Revisiting neighbor discovery with interferences consideration

    Elyes Ben Hamida   Guillaume Chelius   Eric Fleury  

    In wireless multi-hop networks; hello protocols for neighbor discovery are a basic service offered by the networking stack. However; their study usually rely on rather simplistic models which do not take into account problems resulting from low level layers; such as the physical layer. One of the peculiarities of radio communications is the presence of interferences which decrease the capacity of the medium.In this paper; we consider a random hello protocol inspired by aloha and we study the impact of the interferences on the neighbor discovery process. As expected; we prove that; in average and in the presence of interferences; a node discovers only a subset of its neighbors. We propose then an analytical model to compute the average number of nodes that a given node may expect to discover in its neighborhood.Finally; we present a hello protocol with sleep periods. We show how to optimize this protocol using our hybrid model. A real scenario stemming from the CAPNET project is then analyzed and studied.
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  • Hydrogen evolution and its effects on cold rolling behavior in commercial pure titanium

    Jing Wen   Nathalie Allain   Eric Fleury  

    Abstract The microstructural evolution induced by hydrogen in the commercially pure Ti50A and its effect on the deformation mechanisms during symmetrical cold rolling have been investigated by means of X-ray diffraction, scanning electron microscopy equipped with electron backscatter diffraction and transmission electronic microscopy. Upon charging by electrolytic method, both δ-TiH x and ε-TiH 2 titanium hydrides were found to precipitate in the grain boundaries as well as within the α-phase matrix. In addition to the refinement of the microstructure, microstructural analyses of the cold rolled samples highlighted the formation of { 10 1 ̅ 2 }⟨ 1 ̅ 011 ⟩ tension twins and { 11 2 ̅ 2 }⟨ 11 2 ̅ 3 ̅ ⟩ compression twins in the hydrogenated samples rather than the { 11 2 ̅ 1 }⟨ 1 ̅ 1 ̅ 26 ⟩ tension twins usually activated in the hydrogen-free Ti50A. No evidence of correlation between the hydrides and twin formations could be detected however measurements of the local lattice curvature and strain gradients from EBSD analyses revealed a larger density of the geometrically necessary dislocations in the hydrogenated samples that could be attributed to the presence of hydrides and hydrogen dissolved in the solid solution α-phase. Highlights • Hydrogen induced microstructure evolution is quantitatively inspected by EBSD. • Hydrogen can facilitate the formation of tension twin { 10 1 ̅ 2 } < 1 ̅ 011 > upon cold rolling. • Hydride-induced deformation heterogeneity leads to the microstructure refinement under plastic deformation. • The formation of the geometrically necessary dislocations can be promoted in the presence of hydrogen during cold deformation.
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