Génétique évolutive d'un cas extrême de polymorphisme de la coloration du plumage chez un oiseau insulaire, Zosterops borbonicus (Zosteropideae)

Les polymorphismes de coloration sont d'un intérêt tout particulier en biologie évolutive. Accessibles, impliqués dans de nombreux processus sélectifs, ils ont grandement contribué à notre compréhension de la mise en place de la diversité biologique. Nous avons étudié un cas de polymorphisme à petite échelle chez Zosterops borbonicus en usant d'approches indirectes de génétique et de génomique. Il apparaît que les changements de couleur ne reposent pas sur des gènes précédemment identifiés comme points chauds évolutifs. Nous identifions également un locus associé à la couleur du plumage sur le chromosome 1 jamais mis en évidence auparavant. De grands effectifs et un flux de gènes limité favorisent l'action de la sélection à petite échelle. Cette étude illustre comment des approches indirectes peuvent permettre d'établir le contexte d'apparition de la diversité phénotypique.Color polymorphisms are of considerable interest in evolutionary biology. As they are accessible and involved in a variety of selective processes, they have contributed significantly to our understanding of biological diversity. We studied a case of polymorphism at a small spatial scale in Zosterops borbonicus, using indirect approaches such as population genetics and genomics. It appears that coloration changes are not due to genes classically described as 'evolutionary hotspots'. We also identified a locus linked to coloration on chromosome 1. This locus is not yet described as affecting feathers or hair coloration. High effective population sizes and moderate gene flow have probably favored selective effects in shaping this polymorphism. This study illustrates how indirect approaches can allow inferring the context in which phenotypic diversity occurs

DC-powered Fe3+:sapphire Maser and its Sensitivity to Ultraviolet Light

The zero-field Fe3+:sapphire whispering-gallery-mode maser oscillator exhibits several alluring features: Its output is many orders of magnitude brighter than that of an active hydrogen maser and thus far less degraded by spontaneous-emission (Schawlow-Townes) and/or receiving-amplifier noise. Its oscillator loop is confined to a piece of mono-crystalline rock bolted into a metal can. Its quiet amplification combined with high resonator Q provide the ingredients for exceptionally low phase noise. We here concentrate on novelties addressing the fundamental conundrums and technical challenges that impede progress. (1) Roasting: The "mase-ability" of sapphire depends significantly on the chemical conditions under which it is grown and heat-treated. We provide some fresh details and nuances here. (2) Simplification: This paper obviates the need for a Ka-band synthesizer: it describes how a 31.3 GHz loop oscillator, operating on the preferred WG pump mode, incorporating Pound locking, was built from low-cost components. (3) "Dark Matter": A Siegman-level analysis of the experimental data determines the substitutional concentration of Fe3+ in HEMEX to be less than a part per billion prior to roasting and up to a few hundred ppb afterwards. Chemical assays, using different techniques (incl. glow discharge mass spectra spectroscopy and neutron activation analysis) consistently indicate, however, that HEMEX contains iron at concentrations of a few parts per million. Drawing from several forgotten-about/under-appreciated papers, this substantial discrepancy is addressed. (4) Excitons: Towards providing a new means of controlling the Fe3+:sapph. system, a cryogenic sapphire ring was illuminated, whilst masing, with UV light at wavelengths corresponding to known electronic and charge-transfer (thus valence-altering) transitions. Preliminary experiments are reported.Comment: pdf only; submitted to the proceedings of the 24th European Frequency and Time Forum, 13-15th April, 201

Fracture of heterogeneous graded materials : from microstructure to structure

10.1016/j.engfracmech.2007.07.017This paper presents a new computational approach dedicated to the fracture of nonlinear heterogeneous materials. This approach extends the standard periodic homogenization problem to a two field cohesive-volumetric finite element scheme. This two field finite element formulation is written as a generalization Non-Smooth Contact Dynamics framework involving Frictional Cohesive Zone Models. The associated numerical platform allows to simulate, at finite strain, the fracture of nonlinear composites from crack initiation to post-fracture behavior. The ability of this computational approach is illustrated by the fracture of the hydrided Zircaloy under transient loading

Influence of the ESR saturation on the power sensitivity of cryogenic sapphire resonators

Here, we study the paramagnetic ions behavior in presence of a strong microwave electromagnetic field sustained inside a cryogenic sapphire whispering gallery mode resonator. The high frequency measurement resolution that can be now achieved by comparing two CSOs permit for the first time to observe clearly the non-linearity of the resonator power sensitivity. These observations that in turn allow us to optimize the CSO operation, are well explained by the Electron Spin Resonance (ESR) saturation of the paramagnetic impurities contained in the sapphire crystal.Comment: 8 pages, 9 figure

Compact Yb+^+ optical atomic clock project: design principle and current status

We present the design of a compact optical clock based on the $^2S_{1/2} \rightarrow ^2D_{3/2}$ 435.5 nm transition in $^{171}$Yb$^+$. The ion trap will be based on a micro-fabricated circuit, with surface electrodes generating a trapping potential to localize a single Yb ion a few hundred $\mu$m from the electrodes. We present our trap design as well as simulations of the resulting trapping pseudo-potential. We also present a compact, multi-channel wavelength meter that will permit the frequency stabilization of the cooling, repumping and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion. We use this wavelength meter to characterize and stabilize the frequency of extended cavity diode lasers at 369.5 nm and 638.6 nm.Comment: 7 pages, 5 figures. Proc. of the 8th FSM 2015, Potsdam, Germany. To be published in IOP Journal of Physics: Conference Serie