Stochastic flowering phenology in Dactylis Glomerata populations described by Markov chain modelling

Understanding the relationship between flowering patterns and pollen dispersal is important in climate change modelling, pollen forecasting, forestry and agriculture. Enhanced understanding of this connection can be gained through detailed spatial and temporal flowering observations on a population level, combined with modelling simulating the dynamics. Species with large distribution ranges, long flowering seasons, high pollen production and naturally large populations can be used to illustrate these dynamics. Revealing and simulating species-specific demographic and stochastic elements in the flowering process will likely be important in determining when pollen release is likely to happen in flowering plants. Spatial and temporal dynamics of eight populations of Dactylis glomerata were collected over the course of two years to determine high-resolution demographic elements. Stochastic elements were accounted for using Markov Chain approaches in order to evaluate tiller-specific contribution to overall population dynamics. Tiller-specific developmental dynamics were evaluated using three different RV matrix correlation coefficients. We found that the demographic patterns in population development were the same for all populations with key phenological events differing only by a few days over the course of the seasons. Many tillers transitioned very quickly from non-flowering to full flowering, a process that can be replicated with Markov Chain modelling. Our novel approach demonstrates the identification and quantification of stochastic elements in the flowering process of D. glomerata, an element likely to be found in many flowering plants. The stochastic modelling approach can be used to develop detailed pollen release models for Dactylis, other grass species and probably other flowering plants

Sur certains 'el'ements r'eguliers des groupes de Weyl et les vari'et'es de Deligne--Lusztig associ'ees

Introduction Cet article est une 'etape vers la compr'ehension de la forme particuli`ere que prennent, dans le cas des groupes r'eductifs finis G F , les conjectures g'en'erales 'enonc'ees dans [Br] pour les blocs `a groupes de d'efaut ab'eliens des groupes finis "abstraits". Apr`es avoir v'erifi'e l'aspect de ces conjectures portant sur les caract`eres des groupes r'eductifs finis (cf. [BrMaMi]), il reste `a 'etablir la version, beaucoup plus profonde et difficile, portant sur les 'equivalences de cat'egories d'eriv'ees concern'ees. Certaines de ces 'equivalences devraient en particulier etre fournies par les cohomologies 'etales de faisceaux convenables sur les vari'et'es de Deligne-Lusztig Xw associ'ees `a certains 'el'ements r'eguliers w du groupe de Weyl W de G (cf. [BrMa], x1). Ceci implique des propri'et'es particuli`eres de la cohomologie 'e

An experimental characterization of Au- and Ru- based microcontacts for MEMS switches

International audienceFrom several years, NOVA MEMS has developed a new set-up for the characterization of contact materials used in micro- switches. Comparisons between several pairs of contact materials have been done with this methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the underlying physics that drives the surface-related failure modes. The data provides a better understanding of micro-contact behaviour related to the impact of current at low- to mediumpower levels. The decrease of the contact resistance, when the contact force increases, is measured for contact pairs of soft material (Au/Au contact), harder materials (Ru/Ru and Rh/Rh contacts) and mixed configuration (Au/Ru and Au/Ni contacts). The super-temperatures of the contacts have been calculated and compared to the theoretical values of softening temperature for each material. It can be shown that this temperature can be reached for gold, ruthenium and rhodium material, with different levels of current intensity. However, no softening behaviour has been highlighted for mixed contact. An enhanced stability of the bimetallic contacts Au/Ru and Au/Ni was demonstrated considering sensitivity to power increase, related to thermo-mechanical deformations and topological modifications of the contact asperities. These results are discussed in a theoretical way by considering the temperature distr