229,540 research outputs found
Content-access QoS in peer-to-peer networks using a fast MDS erasure code
This paper describes an enhancement of content access Quality of Service in peer to peer (P2P) networks. The main idea is to use an erasure code to distribute the information over the peers. This distribution increases the usersâ choice on disseminated encoded data and therefore statistically enhances the overall throughput of the transfer. A performance evaluation based on an original model using the results of a measurement campaign of sequential and parallel downloads in a real P2P network over Internet is presented. Based on a bandwidth distribution, statistical content-access QoS are guaranteed in function of both the content replication level in the network and the file dissemination strategies. A simple application in the context of media streaming is proposed. Finally, the constraints on the erasure code related to the proposed system are analysed and a new fast MDS erasure code is proposed, implemented and evaluated
Self-Organizing Flows in Social Networks
Social networks offer users new means of accessing information, essentially
relying on "social filtering", i.e. propagation and filtering of information by
social contacts. The sheer amount of data flowing in these networks, combined
with the limited budget of attention of each user, makes it difficult to ensure
that social filtering brings relevant content to the interested users. Our
motivation in this paper is to measure to what extent self-organization of the
social network results in efficient social filtering. To this end we introduce
flow games, a simple abstraction that models network formation under selfish
user dynamics, featuring user-specific interests and budget of attention. In
the context of homogeneous user interests, we show that selfish dynamics
converge to a stable network structure (namely a pure Nash equilibrium) with
close-to-optimal information dissemination. We show in contrast, for the more
realistic case of heterogeneous interests, that convergence, if it occurs, may
lead to information dissemination that can be arbitrarily inefficient, as
captured by an unbounded "price of anarchy". Nevertheless the situation differs
when users' interests exhibit a particular structure, captured by a metric
space with low doubling dimension. In that case, natural autonomous dynamics
converge to a stable configuration. Moreover, users obtain all the information
of interest to them in the corresponding dissemination, provided their budget
of attention is logarithmic in the size of their interest set
Freeze the BCI until the user is ready: a pilot study of a BCI inhibitor
In this paper we introduce the concept of Brain-Computer Interface (BCI)
inhibitor, which is meant to standby the BCI until the user is ready, in order
to improve the overall performance and usability of the system. BCI inhibitor
can be defined as a system that monitors user's state and inhibits BCI
interaction until specific requirements (e.g. brain activity pattern, user
attention level) are met. In this pilot study, a hybrid BCI is designed and
composed of a classic synchronous BCI system based on motor imagery and a BCI
inhibitor. The BCI inhibitor initiates the control period of the BCI when
requirements in terms of brain activity are reached (i.e. stability in the beta
band). Preliminary results with four participants suggest that BCI inhibitor
system can improve BCI performance.Comment: 5th International Brain-Computer Interface Workshop (2011
Theoretical and Econometric Analysis of Behaviours Toward Environment.
no abstract availableEnvironmental economics;
Electrochemical behaviour of thorium(IV) in molten LiFâCaF2 medium on inert and reactive electrodes
The electrochemicalbehaviour of the Th(IV)/Th system was examined in moltenLiFâCaF2medium on inert (molybdenum), reactive (nickel) and liquid (bismuth) electrodes in the 810â920 °C temperature range by several electrochemical techniques. Experimental results showed that (i) thorium fluoride was reduced in a single step exchanging 4 electrons and limited by thorium ions diffusion in the solution, (ii) the oxide ions induce the precipitation of Th(IV) in the form of thorium oxide (ThO2), in a process involving as intermediate compound a soluble oxifluoride (ThOF2), (iii) the reduction of thorium ions on reactive (Ni and liquid Bi) electrodes yields compounds NiâTh and BiâTh with a potential shift of around 0.7 V (for Ni and Bi) more anodic than the reduction of Th(IV) on inert substrate
The Plateau problem at infinity for horizontal ends and genus 1
In this paper, we study Alexandrov-embedded r-noids with genus 1 and
horizontal ends. Such minimal surfaces are of two types and we build several
examples of the first one. We prove that if a polygon bounds an immersed
polygonal disk, it is the flux polygon of an r-noid with genus 1 of the first
type. We also study the case of polygons which are invariant under a rotation.
The construction of these surfaces is based on the resolution of the Dirichlet
problem for the minimal surface equation on an unbounded domain.Comment: 63 page
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