Polarons as stable solitary wave solutions to the Dirac-Coulomb system

We consider solitary wave solutions to the Dirac--Coulomb system both from physical and mathematical points of view. Fermions interacting with gravity in the Newtonian limit are described by the model of Dirac fermions with the Coulomb attraction. This model also appears in certain condensed matter systems with emergent Dirac fermions interacting via optical phonons. In this model, the classical soliton solutions of equations of motion describe the physical objects that may be called polarons, in analogy to the solutions of the Choquard equation. We develop analytical methods for the Dirac--Coulomb system, showing that the no-node gap solitons for sufficiently small values of charge are linearly (spectrally) stable.Comment: Latex, 26 page

Stable directions for small nonlinear Dirac standing waves

We prove that for a Dirac operator with no resonance at thresholds nor eigenvalue at thresholds the propagator satisfies propagation and dispersive estimates. When this linear operator has only two simple eigenvalues close enough, we study an associated class of nonlinear Dirac equations which have stationary solutions. As an application of our decay estimates, we show that these solutions have stable directions which are tangent to the subspaces associated with the continuous spectrum of the Dirac operator. This result is the analogue, in the Dirac case, of a theorem by Tsai and Yau about the Schr\"{o}dinger equation. To our knowledge, the present work is the first mathematical study of the stability problem for a nonlinear Dirac equation.Comment: 62 page

Genetic diversity of North African Thymus algeriensis in Tunisia: Population structure and implication for conservation

The genetic diversity within and among nine natural populations of Thymus hirtus Willd. subsp. algeriensis (Boiss. et Reut.) Murb. from different geographical and bioclimatic zones were assessed using Random Amplified Polymorphic DNA data. A total of 154 bands were generated from seven selected primers. 141 bands were polymorphic (P=91.56%). The genetic diversity within a population based on Shannon's index which was high (H' pop=0.307) and varied according to bioclimatic zones. Ahigh genetic differentiation among populations (G ST=0.335 and F{cyrillic} ST=0.296) was revealed, suggesting a population isolation and a low level of gene flow among them. The major proportion of the variation was attributable to individual differences within populations. The genetic structure is in accordance with geography distances. The Neighbour- joining tree based on Nei's and Li's genetic distance among individuals showed that individuals from each population clustered together. The UPGMA dendrogram based on F{cyrillic} ST values revealed three clusters each of them includes populations closuring to their geographical origin. The high genetic structure of populations resulted from genetic drift caused both by the habitat fragmentation and the low size of most populations. The in situ conservation should interest all populations. The ex situ conservation should be based on the collection of seeds rather within than among populations because of the maximum of variation was revealed within populations.Esta investigación fue financiada por una beca del Ministerio de Investigación, Ciencia y Tecnología y el Instituto Nacional de Ciencias Aplicadas y Tecnología (Beca de Investigación 99 / UR/09-10).Esta investigación fue financiada por una beca del Ministerio de Investigación, Ciencia y Tecnología y el Instituto Nacional de Ciencias Aplicadas y Tecnología (Beca de Investigación 99 / UR/09-10)Peer Reviewe

A survey on search-based model-driven engineering

International audienceModel-driven engineering (MDE) and search-based software engineering (SBSE) are both relevant approaches to software engineering. MDE aims to raise the level of abstraction in order to cope with the complexity of software systems, while SBSE involves the application of metaheuristic search techniques to complex software engineering problems, reformulating engineering tasks as optimization problems. The purpose of this paper is to survey the relatively recent research activity lying at the interface between these two fields, an area that has come to be known as search-based model-driven engineering. We begin with an introduction to MDE, the concepts of models, of metamodels and of model transformations. We also give a brief introduction to SBSE and metaheuristics. Then, we survey the current research work centered around the combination of search-based techniques and MDE. The literature survey is accompanied by the presentation of references for further details

A comparative study of modified BBO variants and other metaheuristics for optimal power allocation in wireless sensor networks

International audienceno abstrac

Genetic diversity of wild Thymus capitatus (Lamiaceae) in Tunisia using molecular markers

In Tunisia, Thymus capitatus L. populations are severely destroyed due to deforestation and over-collecting. The species occurs in small scattered populations decreasing progressively in size. Yet, no conservation or improvement programs are attempted to preserve and promote the potential value of this resource. In this work, we assessed the genetic diversity of nine Tunisian populations of Thymus capitatus L. from different bioclimates, using 103 polymorphic randomly amplified polymorphic DNA (RAPD) loci. The analysis of the genetic variation within and among populations is primordial to elaborate conservation and improvement programs. The species showed a low diversity within populations (0.276<H’<0.327) due to genetic drift caused by the habitat fragmentation. A high genetic differentiation (GST=0.359 and ΦST=0.284) and a low gene flow (0.435<Nm<0.970) among populations, indicating a short seed and/or pollen dispersal distance, were revealed. The absence of isolation by distance and the high level of differentiation among populations suggested the existence of important historical gene flow between them. The UPGMA dendrogram analysis basedon ΦST distance matrix showed that most populations clustered independently to bioclimate or geographical distance indicating that genetic differentiation mainly occurs at local space scale due to genetic drift. Given the high proportion of the within-population diversity and the high amount of among populations variation, the ex-situ conservation should be made by the collection of seeds/cuttings rather within than among populations. The in-situ conservation should be made appropriately according to populations in their bioclimate

Hybrid BBO-DE algorithms for fuzzy entropy-based thresholding

International audienceno abstrac

Genetic diversity and structure of wild Tunisian Thymus capitatus (L.) Hoffm. et Link. (Lamiaceae) assessed using isozyme markers

The genetic diversity and population structure of 25 natural populations of Thymus capitatus, from five ecological areas, were analysed using eight isozymes. For all populations, 11 polymorphic loci were detected, and several of them showed rare alleles. A high genetic diversity within populations (A p=1.82; P=62.88%; H o=0.116) and an excess of heterozygosity were observed. A high level of inbreeding within populations was observed (F IS=0.471). High differentiation and low gene flow (N m=0.821) were detected among populations (F ST=0.219). The genetic variation within and among ecological groups varied according to the bioclimate. Population structuration depends on geographic distance between sites rather than on bioclimate (Mantel's test; r=0.251; P=0.004). Nei's genetic distances (D) values calculated between pairs of populations were globally low with a mean of 0.047. The unweighted pairwise groups method using arithmetic average dendrogram showed fourth sub-clusters. Population groupings occur with evident relationship to geographic location. The substantial differentiation and the high genetic similarities between populations indicate that populations have been recently isolated as a result of anthropic pressure. In situ conservation must first focus on populations with a high level of genetic diversity and rare alleles. Ex situ preservation should be elaborated by collecting seeds within populations that showed a high level of genetic diversity in each ecological group. © 2011 Blackwell Publishing Ltd.This research was supported by a grant of the Ministry of Scientific Research and Technology and the National Institute of Applied Science and Technology (Research grant 99/UR/09-10).Peer Reviewe