Trapping Set Enumerators for Repeat Multiple Accumulate Code Ensembles

The serial concatenation of a repetition code with two or more accumulators has the advantage of a simple encoder structure. Furthermore, the resulting ensemble is asymptotically good and exhibits minimum distance growing linearly with block length. However, in practice these codes cannot be decoded by a maximum likelihood decoder, and iterative decoding schemes must be employed. For low-density parity-check codes, the notion of trapping sets has been introduced to estimate the performance of these codes under iterative message passing decoding. In this paper, we present a closed form finite length ensemble trapping set enumerator for repeat multiple accumulate codes by creating a trellis representation of trapping sets. We also obtain the asymptotic expressions when the block length tends to infinity and evaluate them numerically.Comment: 5 pages, to appear in proc. IEEE ISIT, June 200

Colonization and dispersal patterns of the invasive American brine shrimp Artemia franciscana (Branchiopoda: Anostraca) in the Mediterranean region

Cysts of the brine shrimp Artemia franciscana are harvested from the Great Salt Lake (GSL) and San Francisco Bay (SFB) saltworks in the USA, and marketed worldwide to provide live food for aquaculture. This species has become invasive across several countries. We investigated (1) if the introduced populations in the Mediterranean region could have originated from these USA populations, (2) how the genetic diversity of Mediterranean compares to that at GSL and SFB, and (3) if genetic patterns in the Mediterranean can shed light on colonization routes. We sequenced a fragment of the cytochrome c oxidase subunit I and screened microsatellites loci from Mediterranean populations and the two putative USA sources. Haplotypes from Mediterranean populations were identical or closely related to those from SFB and GSL, and not related to other available American populations. Microsatellite analyses showed a reduced population diversity for most Mediterranean populations suggesting bottleneck effects, but few populations were showing similar or higher genetic diversity than native ones, which are likely to be admixed from both GSL and SFB because of multiple introductions. Results suggest natural dispersal, potentially via flamingos, between two Spanish populations. Our analyses show that all invaded populations could have originated from those commercialized USA populations. © 2013 Springer Science+Business Media Dordrecht

Effects of woody vegetation patches on species composition in Stipa tenacissima steppes

Stipa tenacissima steppes cover 70, 000 km2 in the Mediterranean basin. In these habitats, resprouting shrubs form woody patches that were removed in the past to promote fiber and forage production. Patches are recovering after decades of abandonment. Patches enhance plant richness and affect ecosystem functioning. Yet, they have been commonly considered as a single entity, paying scarce attention to patch heterogeneity, patch dynamics and their impact on community composition. We describe the physical and biotic structure of 450 patches in 15 catchments along a climate gradient in southeastern Spain, and analyze the drivers of overstory and understory composition and recruitment of patch-forming species. Patches were formed by one to six species (Quercus coccifera, Juniperus oxycedrus, Rhamnus lycioides, Ephedra fragilis, Pistacia lentiscus and Osyris lanceolata). Climate determined the species composition in each patch, their physical characteristics and the recruitment of patch-forming species. Species cover and richness depended on the dominant species. Our results suggest that patches dominated by Quercus coccifera and Juniperus oxycedrus may decline and patches dominated by Rhamnus lycioides and Ephedra fragilis may expand as climate warms. They also provide new insights on the interactions in patch communities very relevant for the conservation and management of S. tenacissima steppes

On a nonlinear subdivision scheme avoiding Gibbs oscillations and converging towards CsC^{s} functions with s>1s>1

International audienceThis paper presents a new nonlinear dyadic subdivision scheme eliminating the Gibbs oscillations close to discontinuities. Its convergence , stability and order of approximation are analyzed. It is proved that this scheme converges towards limit functions Hölder continuous with exponent larger than 1.299. Numerical estimates provide a Hölder exponent of 2.438. This subdivision scheme is the first one that simultaneously achieves the control of the Gibbs phenomenon and has limit functions with Hölder exponent larger than 1

Analysis and Design of Tuned Turbo Codes

It has been widely observed that there exists a fundamental trade-off between the minimum (Hamming) distance properties and the iterative decoding convergence behavior of turbo-like codes. While capacity achieving code ensembles typically are asymptotically bad in the sense that their minimum distance does not grow linearly with block length, and they therefore exhibit an error floor at moderate-to-high signal to noise ratios, asymptotically good codes usually converge further away from channel capacity. In this paper, we introduce the concept of tuned turbo codes, a family of asymptotically good hybrid concatenated code ensembles, where asymptotic minimum distance growth rates, convergence thresholds, and code rates can be traded-off using two tuning parameters, {\lambda} and {\mu}. By decreasing {\lambda}, the asymptotic minimum distance growth rate is reduced in exchange for improved iterative decoding convergence behavior, while increasing {\lambda} raises the asymptotic minimum distance growth rate at the expense of worse convergence behavior, and thus the code performance can be tuned to fit the desired application. By decreasing {\mu}, a similar tuning behavior can be achieved for higher rate code ensembles.Comment: Accepted for publication in IEEE Transactions on Information Theor

Multifunctional device for bicycles

This paper aims at designing a "Multifunctional device composed of load support and anti-theft lock for standard bicycles". A previous study has been developed in order to justify and validate the final design of the unmet needs of people in their daily lives, with an emphasis on satisfying those that imply specific savings, whether economic, energy or time. As a result, the use of bicycles as a means of transport in Spain is promoted taking as a frame of reference countries such as the Netherlands or France. This means economic and energy savings (by replacing the car) and an improvement in people's health and quality of life. Following the steps of the design methodology, once the need was detected, an information search was carried out in order to identify and prioritize the design specifications that meet the demands of potential customers. For this reason, various sources were used, The boost to use bicycles has allowed to establish a set of measurements and specifications in the design of the device with a double functionality, the transport of merchandise and an anti-theft system. In addition to meeting the needs of the client, the design must comply with a set of reference regulations both, at the level of security devices and the transport of merchandise at retail. The result of the work has given rise to patent application with prior examination at a national level, in a first phase, and subsequently, at an international level.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech