Improvement of the Tm3+:3H4 level lifetime in silica optical fibres by lowering the local phonon energy

The role of some glass network modifiers on the quantum efficiency of the near-infrared fluorescence from the 3H4 level of Tm3+ ion in silica-based doped fibres is studied. Modifications of the core composition affect the spectroscopic properties of Tm3+ ion. Adding 17.4 mol% of AlO3/2 to the core glass caused an increase of the 3H4 level lifetime up to 50 $\mu$s, 3.6 times higher than in pure silica glass. The quantum efficiency was increased from 2% to approximately 8%. On the opposite, 8 mol% of PO5/2 in the core glass made the lifetime decrease downto 9 $\mu$s. These changes of Tm3+ optical properties are assigned to the change of the local phonon energy to which they are submitted by modifiers located in the vicinity of the doping sites. Some qualitative predictions of the maximum achievable quantum efficiency are possible using a simple microscopic model to calculate the non-radiative de-excitation rates

Two identification tools applied on Mascarene’s corals genera (Xper2) and species (IKBS)

For future biodiversity studies relying on species identification, environmental officers and researchers will only be left with monographic descriptions and collections in museums. This is why a knowledge base on the zooxanthellate scleractinian corals of the Mascarene Archipelago is being developed. This project offers results for both biologists/taxonomists and students or MPA-teams. Two online computer-based applications permit to identify genera and species. The first identification tool, called Xper², was developed by LIS (Informatic and Systematics Laboratory) in Paris, and is used for identifications to genera. The second tool, named IKBS (Iterative Knowledge Base System), was developed by IREMIA (Institute for Research in Applied Mathematics and Computer Science) in La Réunion, and is used for identifications from families to species. The tools presently work for Astrocoeniidae, Pocilloporidae, Acroporidae (only Acropora + Isopora), Psammocoridae, Siderastreidae (owns Psammocoridae as genera), Fungiidae, Poritidae, Faviidae Faviinae, Faviidae Montastreinae, Mussidae. We plan to start a new phase to add the last families, fully translate the web site in English and extend the Xper² identification to all the western Indian Ocean genera

Expression of stress-related genes in tomato plants exposed to arsenic and chromium in nutrient solution

International audienceThe molecular responses of hydroponically cultivated tomato plants to As(V) or Cr(VI) were assessed by transcript accumulation analysis of genes coding for products potentially involved in heavy metal tolerance. A quantitative real-time PCR experiment was performed with Hsp90-1, MT2- and GR1-like protein genes using RNA isolated from tomato roots or shoots treated for 24 h with As(V) or Cr(VI) at concentrations ranging from 80 to 640 μM. Both transient metallic treatments induced Hsp90-1 transcript accumulation in tomato plants. MT2- and GR1-like transcripts accumulated in tomato roots treated with As(V) but were only slightly affected by Cr(VI) treatment. Tomatoes showed phenotypic symptoms to heavy metal toxicity when plants were exposed to Cr(VI) but not As(V). Plant lethality was observed at 1280 μM Cr(VI), indicating that tomatoes were more tolerant to As than Cr stress under the experimental conditions used here

Upper bound on the density of Ruelle resonances for Anosov flows

Using a semiclassical approach we show that the spectrum of a smooth Anosov vector field V on a compact manifold is discrete (in suitable anisotropic Sobolev spaces) and then we provide an upper bound for the density of eigenvalues of the operator (-i)V, called Ruelle resonances, close to the real axis and for large real parts.Comment: 57 page

Thulium environment in a silica doped optical fibre

Thulium-doped optical fibre amplifiers (TDFA) are developed to extend the optical telecommunication wavelength division multiplexing (WDM) bandwidth in the so-called S-band (1460-1530 nm). The radiative transition at 1.47 lm (3H4 -> 3F4) competes with a non-radiative multi-phonon de-excitation (3H4 -> 3H5). The quantum efficiency of the transition of interest is then highly affected by the phonon energy (Ep) of the material. For reliability reasons, oxide glasses are preferred but suffer from high phonon energy. In the case of silica glass, Ep is around 1100 cm-1 and quantum efficiency is as low as 2%. To improve it, phonon energy in the thulium environment must be lowered. For that reason, aluminium is added and we explore three different core compositions: pure silica, and silica slightly modified with germanium or phosphorus. The role of aluminium is studied through fluorescence decay curves, fitted according to the continuous function decay analysis. From this analysis, modification of the thulium local environment due to aluminium is evidenced

The Results of Meadows and Cliff Are Wrong Because They Compute Indicator y Before Model Convergence

Meadows and Cliff (2012) failed to replicate the results of Deffuant et al. (2002) and concluded that our paper was wrong. In this note, we show that the conclusions of Meadows and Cliff are due to a wrong computation of indicator y, which was not fully specified in our 2002 paper. In particular, Meadows and Cliff compute indicator y before model convergence whereas this indicator should be computed after model convergence

Semiclassical measures and the Schroedinger flow on Riemannian manifolds

In this article we study limits of Wigner distributions (the so-called semiclassical measures) corresponding to sequences of solutions to the semiclassical Schroedinger equation at times scales $\alpha_{h}$ tending to infinity as the semiclassical parameter $h$ tends to zero (when $\alpha _{h}=1/h$ this is equivalent to consider solutions to the non-semiclassical Schreodinger equation). Some general results are presented, among which a weak version of Egorov's theorem that holds in this setting. A complete characterization is given for the Euclidean space and Zoll manifolds (that is, manifolds with periodic geodesic flow) via averaging formulae relating the semiclassical measures corresponding to the evolution to those of the initial states. The case of the flat torus is also addressed; it is shown that non-classical behavior may occur when energy concentrates on resonant frequencies. Moreover, we present an example showing that the semiclassical measures associated to a sequence of states no longer determines those of their evolutions. Finally, some results concerning the equation with a potential are presented.Comment: 18 pages; Theorems 1,2 extendend to deal with arbitrary time-scales; references adde

Quantisations of piecewise affine maps on the torus and their quantum limits

For general quantum systems the semiclassical behaviour of eigenfunctions in relation to the ergodic properties of the underlying classical system is quite difficult to understand. The Wignerfunctions of eigenstates converge weakly to invariant measures of the classical system, the so called quantum limits, and one would like to understand which invariant measures can occur that way, thereby classifying the semiclassical behaviour of eigenfunctions. We introduce a class of maps on the torus for whose quantisations we can understand the set of quantum limits in great detail. In particular we can construct examples of ergodic maps which have singular ergodic measures as quantum limits, and examples of non-ergodic maps where arbitrary convex combinations of absolutely continuous ergodic measures can occur as quantum limits. The maps we quantise are obtained by cutting and stacking

When the nose must remain responsive: glutathione conjugation of the mammary pheromone in the newborn rabbit

In insects, xenobiotic-metabolizing enzymes were demonstrated to regulate pheromones inactivation, clearing them from the olfactory periphery and keeping receptors ready for stimulation renewal. Here, we investigate whether similar processes could occur in mammals, focusing on the pheromonal communication between female rabbits and their newborns. Lactating rabbits emit in their milk a volatile aldehyde, 2-methylbut-2-enal, that elicits searching-grasping in neonates; called the mammary pheromone (MP), it is critical for pups which are constrained to find nipples within the 5 min of daily nursing. For newborns, it is thus essential to remain sensitive to this odorant during the whole nursing period to display several actions of sucking. Here, we show that the MP is enzymatically conjugated to glutathione in newborn olfactory epithelium (OE), in accordance with the high mRNA expression of glutathione transferases evidenced by quantitative reverse transcription-PCR. This activity in the nose is higher than in the liver and in OE of newborns compared with weanlings (no more responsive to the pheromone). Therefore, the results pinpoint the existence of a high level of MP-glutathione conjugation activity in the OE of young rabbits, especially in the developmental window where the perceptual sensitivity toward the MP is crucial for survival

Entropic bounds on semiclassical measures for quantized one-dimensional maps

Quantum ergodicity asserts that almost all infinite sequences of eigenstates of a quantized ergodic system are equidistributed in the phase space. On the other hand, there are might exist exceptional sequences which converge to different (non-Liouville) classical invariant measures. By the remarkable result of N. Anantharaman and S. Nonnenmacher math-ph/0610019, arXiv:0704.1564 (with H. Koch), for Anosov geodesic flows the metric entropy of any semiclassical measure must be bounded from below. The result seems to be optimal for uniformly expanding systems, but not in general case, where it might become even trivial if the curvature of the Riemannian manifold is strongly non-uniform. It has been conjectured by the same authors, that in fact, a stronger bound (valid in general case) should hold. In the present work we consider such entropic bounds using the model of quantized one-dimensional maps. For a certain class of non-uniformly expanding maps we prove Anantharaman-Nonnenmacher conjecture. Furthermore, for these maps we are able to construct some explicit sequences of eigenstates which saturate the bound. This demonstrates that the conjectured bound is actually optimal in that case.Comment: 38 pages, 4 figure