173 research outputs found
Galois invariant smoothness basis
This text answers a question raised by Joux and the second author about the
computation of discrete logarithms in the multiplicative group of finite
fields. Given a finite residue field \bK, one looks for a smoothness basis
for \bK^* that is left invariant by automorphisms of \bK. For a broad class
of finite fields, we manage to construct models that allow such a smoothness
basis. This work aims at accelerating discrete logarithm computations in such
fields. We treat the cases of codimension one (the linear sieve) and
codimension two (the function field sieve)
The geometry of some parameterizations and encodings
We explore parameterizations by radicals of low genera algebraic curves. We
prove that for a prime power that is large enough and prime to , a fixed
positive proportion of all genus 2 curves over the field with elements can
be parameterized by -radicals. This results in the existence of a
deterministic encoding into these curves when is congruent to modulo
. We extend this construction to parameterizations by -radicals for
small odd integers , and make it explicit for
LES COULISSES DE L'ĆUVRE NET ART
La conception des Ćuvres d'art pour ordinateur engage diffĂ©rentes contributions, artistiques et informatiques, qui instaurent un morcellement de l'activitĂ© crĂ©atrice et des modes pluriels de dĂ©signation de ce qui fait "Ćuvre". En amont, l'activitĂ© crĂ©atrice met en scĂšne une polyphonie Ă©nonciative et un travail de nĂ©gociation permanent confrontant des rĂ©gimes et logiques d'actions antagonistes. La mise en scĂšne de l'activitĂ© de conception associe deux formes d'Ă©criture : l'Ă©criture de l'algorithme de programmation d'une part, et l'Ă©criture de l'idĂ©e ou du concept (au sens d'intention) artistique d'autre part. En aval, le dispositif numĂ©rique est tour Ă tour dĂ©signĂ© comme "produit" dissociĂ© de l'Ćuvre comme fragment d'application logicielle ou algorithme informatique, et comme "Ćuvre" intĂ©grant la part informatique du programme. Enfin, le spectateur est Ă son tour associĂ© Ă l'Ćuvre qu'il actualise en contribuant Ă son dĂ©veloppement par l'altĂ©ration de l'idĂ©e initiale ou par l'apport de matĂ©riaux propres. DĂšs lors, l'Ćuvre d'art pour Internet ne correspond plus au concept d'objet achevĂ© et localisable, mais s'inscrit davantage comme un processus, un dispositif collectif ouvert et interactif. Cette communication propose Ă partir d'un dispositif prĂ©cis (Des_Frags) de souligner les dĂ©placements engendrĂ©s par ce partage et cette dĂ©lĂ©gation du processus crĂ©atif sur la notion traditionnelle "d'Ćuvre d'art". Qu'est-ce qui fait "Ćuvre" dans ce contexte ? Quelles en sont les caractĂ©ristiques propres ? Entre avant scĂšne et coulisses, comment est-elle simultanĂ©ment dĂ©signĂ©e, perçue et agie
Elliptic periods for finite fields
We construct two new families of basis for finite field extensions. Basis in
the first family, the so-called elliptic basis, are not quite normal basis, but
they allow very fast Frobenius exponentiation while preserving sparse
multiplication formulas. Basis in the second family, the so-called normal
elliptic basis are normal basis and allow fast (quasi linear) arithmetic. We
prove that all extensions admit models of this kind
OFDR Distributed Temperature and Strain Measurements with Optical Fibre Sensing Cables: Application to Drain Pipeline Monitoring in a Nuclear Power Plant
International audienceThis study deals with the testing of innovative Optical Fibre Sensing (OFS) cables deployed on ducts, with the aim to perform distributed temperature and strain measurements. Such cables contain several optical fibres devoted to be interrogated by Optical Frequency Domain Reflectometry (OFDR). The methodology has first been developed and qualified in laboratory. Then, real tests have been performed on a Nuclear Power Plant (NPP) drain system to demonstrate the industrial feasibility of such technology. To do so, two small diameter sensing cables, compatible with distributed temperature and strain measurements, have been qualified and afterwards installed along a sodium drain line at Superphenix NPP (liquid sodium coolant fast breeder reactor in current dismantling). Measurements have been performed during the preheating operation. Recorded data were post-processed according to a semi-empirical model taking into account temperature dependence and thermo-mechanical sensing cable behaviour. Optical fibre distributed temperature measurements were then successfully compared to thermocouple reference measurements, whereas optical sensing cable data were processed to provide distributed strain, then distributed curvature radius, which will enable, after numerical integration, to compute distributed displacement data. The goal is to assess the use of OFS for monitoring both temperature and mechanical strain distribution along a pipe under heat stress
A faster pseudo-primality test
We propose a pseudo-primality test using cyclic extensions of . For every positive integer , this test achieves the
security of Miller-Rabin tests at the cost of Miller-Rabin
tests.Comment: Published in Rendiconti del Circolo Matematico di Palermo Journal,
Springe
Visualizing Compaction of Polysomes in Bacteria.
International audienceDuring protein synthesis, many translating ribosomes are bound together with an mRNA molecule to form polysomes (or polyribosomes). While the spatial organization of bacterial polysomes has been well studied in vitro, little is known about how they cluster when cellular conditions are highly constrained. To better understand this, we used electron tomography, template matching, and three-dimensional modeling to analyze the supramolecular network of ribosomes after induction of translational pauses. In Escherichia coli, we overexpressed an mRNA carrying a polyproline motif known to induce pausing during translation. When working with a strain lacking transfer-messenger RNA, the principle actor in the "trans-translation" rescuing system, the cells survived the hijacking of the translation machinery but this resulted in a sharp modification of the ribosomal network. The results of our experiments demonstrate that single ribosomes are replaced with large amounts of compacted polysomes. These polysomes are highly organized, principally forming hairpins and dimers of hairpins that stack together. We propose that these spatial arrangements help maintain translation efficiency when the rescue systems are absent or overwhelmed
BIOTEX-biosensing textiles for personalised healthcare management.
Textile-based sensors offer an unobtrusive method of continually monitoring physiological parameters during daily activities. Chemical analysis of body fluids, noninvasively, is a novel and exciting area of personalized wearable healthcare systems. BIOTEX was an EU-funded project that aimed to develop textile sensors to measure physiological parameters and the chemical composition of body fluids, with a particular interest in sweat. A wearable sensing system has been developed that integrates a textile-based fluid handling system for sample collection and transport with a number of sensors including sodium, conductivity, and pH sensors. Sensors for sweat rate, ECG, respiration, and blood oxygenation were also developed. For the first time, it has been possible to monitor a number of physiological parameters together with sweat composition in real time. This has been carried out via a network of wearable sensors distributed around the body of a subject user. This has huge implications for the field of sports and human performance and opens a whole new field of research in the clinical setting
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