On Quasi-Cyclic Codes as a Generalization of Cyclic Codes

In this article we see quasi-cyclic codes as block cyclic codes. We generalize some properties of cyclic codes to quasi-cyclic ones such as generator polynomials and ideals. Indeed we show a one-to-one correspondence between l-quasi-cyclic codes of length m and ideals of M_l(Fq)[X]/(X^m-1). This permits to construct new classes of codes, namely quasi-BCH and quasi-evaluation codes. We study the parameters of such codes and propose a decoding algorithm up to half the designed minimum distance. We even found one new quasi-cyclic code with better parameters than known [189, 11, 125]_F4 and 48 derivated codes beating the known bounds as well.Comment: (18/08/2011

Reconstruction et analyse sémantique de chronologies cybercriminelles

International audienceLa reconstruction de scénarios est l’une des étapes les plus importantes d’une investigation numérique. Elle permet aux enquêteurs d’avoir une vue des évènements survenus durant un incident. La reconstruction de scénarios est une tâche complexe requérant l’étude d’un très grand nombre d’évènements en raison de l’omniprésence des nouvelles technologies dans notre quotidien. De plus, les conclusions produites se doivent de respecter les critères fixés par la justice. Afin de répondre à ces challenges, nous proposons une nouvelle méthodologie, basée sur une ontologie intégrant les connaissances d’experts des domaines de la criminalistique et de l’ingénierie logicielle, permettant d’assister les enquêteurs tout au long du processus d’enquête

A mathematical modeling of catalytic milli-fixed bed reactor for Fischer–Tropsch synthesis: Influence of tube diameter on Fischer Tropsch selectivity and thermal behavior

A two-dimensional pseudo-homogeneous model has been developed to investigate the influence of tube size on the thermal behavior and performance of packed fixed bed reactor for the low temperature Fischer–Tropsch (FT) synthesis over alumina supported cobalt. Velocity, temperature and composition fields are determined by solving the fundamental transport equations in porous media. Special attention was paid to the variation of transport properties with temperature and composition of the gas mixture. High dependency of the thermal behavior on the thermal conductivity of the gas mixture is highlighted, whereas viscosity and heat capacity of gas mixture have very little influence. Moreover for the considered catalyst, simulation results have displayed high heat removal for the millimetric scale with a tube inner diameter below 2.75mm for an extended range of weight hourly space velocity (20–600gsyngasmin−1kgcat.−1, T=493K and P=20bar). With a millimetric reactor, high CO conversion (XCO>90%) is obtained for values of space velocity between 30 and 120gsyngasmin−1kgcat.−1. For higher diameter tube than 3.11mm, thermal runaway occurs and even worse, no convergence achieved due to the very low heat transfer global coefficient and the weak surface/volume ratio, leading to a significant decrease of liquid fuels selectivity and an increase of light hydrocarbon (C1 to C4) selectivity up to 14%. To conclude, results from scale-up study with the millimetric scale are outstanding, more than 2900kgh−1mcat.−3 of C5+ could be produce after numbering-up 3033 tubes of 10 centimeters in length whereas conventional units (multitubular fixed bed reactors or slurry phase reactors) do not exceed 400kgh−1mcat.−3

Ion stopping in dense plasma target for high energy density physics

The basic physics of nonrelativistic and electromagnetic ion stopping in hot and ionized plasma targets is thoroughly updated. Corresponding projectile-target interactions involve enhanced projectile ionization and coupling with target free electrons leading to significantly larger energy losses in hot targets when contrasted to their cold homologues. Standard stoppping formalism is framed around the most economical extrapolation of high velocity stopping in cold matter. Further elaborations pay attention to target electron coupling and nonlinearities due to enhanced projectile charge state, as well. Scaling rules are then used to optimize the enhanced stopping of MeV/amu ions in plasmas with electron linear densities nel ~ 10 18 -10 20 cm -2 . The synchronous firing of dense and strongly ionized plasmas with the time structure of bunched and energetic multicharged ion beam then allow to probe, for the first time, the long searched enhanced plasma stopping and projectile charge at target exit. Laser ablated plasmas (SPQR1) and dense linear plasma columns (SPQR2) show up as targets of choice in providing accurate and on line measurements of plasma parameters. Corresponding stopping results are of a central significance in asserting the validity of intense ion beam scenarios for driving thermonuclear pellets. Other applications of note feature thorium induced fission, novel ion sources and specific material processing through low energy ion beams. Last but not least, the given ion beam-plasma target interaction physics is likely to pave a way to the production and diagnostics of warm dense matter (WDM)

A cost–benefit analysis of acclimation to low irradiance in tropical rainforest tree seedlings: leaf life span and payback time for leaf deployment

The maintenance in the long run of a positive carbon balance under very low irradiance is a prerequisite for survival of tree seedlings below the canopy or in small gaps in a tropical rainforest. To provide a quantitative basis for this assumption, experiments were carried out to determine whether construction cost (CC) and payback time for leaves and support structures, as well as leaf life span (i) differ among species and (ii) display an irradiance-elicited plasticity. Experiments were also conducted to determine whether leaf life span correlates to CC and payback time and is close to the optimal longevity derived from an optimization model. Saplings from 13 tropical tree species were grown under three levels of irradiance. Specific-CC was computed, as well as CC scaled to leaf area at the metamer level. Photosynthesis was recorded over the leaf life span. Payback time was derived from CC and a simple photosynthesis model. Specific-CC displayed only little interspecific variability and irradiance-elicited plasticity, in contrast to CC scaled to leaf area. Leaf life span ranged from 4 months to >26 months among species, and was longest in seedlings grown under lowest irradiance. It was always much longer than payback time, even under the lowest irradiance. Leaves were shed when their photosynthesis had reached very low values, in contrast to what was predicted by an optimality model. The species ranking for the different traits was stable across irradiance treatments. The two pioneer species always displayed the smallest CC, leaf life span, and payback time. All species displayed a similar large irradiance-elicited plasticity

Factorisation in M'(Fq)[X]. Construction of quasi-cyclic codes

International audienceQuasi-cyclic codes are viewed as codes cancelled by polynomials with matricial coefficients. This construction leads to the problem of factorisation of Xm -1 in M'(Fq)[X]. In this paper we deal with the general factorisation in M'(Fq)[X]. Then we give results on the roots and the factorisation of the particular polynomial Xm -1. These factorisations permit the construction of such quasi-cyclic codes. We show that in most cases, these codes meet best known bounds for minimum distances. We even found two new codes with parameters better than known [30; 22; 6]F4 and [29; 21; 6]F4

Semantic Measures: A State of the Art

Significant advances in terms of syntactic, structural and schematic heterogeneity have been achieved by adopting conventions and standards. The IT community is now trying to solve the problem of semantic heterogeneity (particularly in the Semantic Web field). To reach this objective, it is necessary to enable machines to understand the semantics of terms. Semantics, as opposed to syntax, defines the mental representation of concepts corresponding to the symbols used in texts or images. When a person reads a text, he uses a semantization process which enables him to associate an interpretation to each sign identified. This operation uses a number of underlying processes such as measuring semantic distance between the meanings of several terms. Reasoning about the semantic proximity of terms is trivial for a human. However, this task is very complex for machines, and requires access to a large number of definitions of specific field terms