Europium site symmetry in sol gel silicophosphate glass : FLN spectroscopy and Molecular Dynamics simulation

International audienc

Structure de verres de silicophosphate dopés europium : analyse par spectroscopie optique et simulation de dynamique moléculaire

National audienc

Optical and structural properties of Eu3+ doped silicophosphate glasses

National audienc

Effect of CdS nanocrystals on the photoluminescence of Eu3+-doped silicophosphate sol gel glass

In this work, we investigate the effect of co-doping with CdS nanoparticles on the photoluminescence properties of Eu3+ doped silicophosphate glass prepared via the sol gel method. Infrared spectroscopy (FTIR) revealed the insertion of phosphorus within the silicate network. XRD and TEM analyses revealed the presence of CdS nanoparticles dispersed in the glass matrix. Based on the optical study and the effective mass theory for spherical quantum dots, it was found that CdS nanocrystals have a gap of nearly 3.53 eV and a size of 2.42 nm. The enhancement of Eu3+ emission induced by CdS nanocrystals and thermal annealing was assigned to either an energy transfer via defect states or structural alteration of the glass network around the rare earth ions

Investigation of the local environment of Eu3+ in a silicophosphate glass using site-selective spectroscopy and Molecular Dynamics simulations

Silicophosphate glasses (SiO2-P2O5) doped with Eu3+ ions were synthesized by the sol-gel process. Optical properties of these glasses were investigated by means of emission spectra and lifetime measurements. The Fluorescence Line Narrowing (FLN) technique was also used to explore the local structure around the Eu3+ ions in this host and to understand the role of phosphate as a codopant. As it is the case for aluminum, the ability of phosphate to avoid the rare earth clustering was investigated, and the role of this codopant in modifying the local order around the rare earth ion was evidenced. The analysis of the FLN spectra and lifetime measurements is consistent with this interpretation. Molecular Dynamics simulations were performed to evaluate and confirm these structural features. Two classes of europium sites were distinguished in agreement with the experimental characterization

Reticulate evolution: frequent introgressive hybridization among chinese hares (genus lepus) revealed by analyses of multiple mitochondrial and nuclear DNA loci

<p>Abstract</p> <p>Background</p> <p>Interspecific hybridization may lead to the introgression of genes and genomes across species barriers and contribute to a reticulate evolutionary pattern and thus taxonomic uncertainties. Since several previous studies have demonstrated that introgressive hybridization has occurred among some species within <it>Lepus</it>, therefore it is possible that introgressive hybridization events also occur among Chinese <it>Lepus </it>species and contribute to the current taxonomic confusion.</p> <p>Results</p> <p>Data from four mtDNA genes, from 116 individuals, and one nuclear gene, from 119 individuals, provides the first evidence of frequent introgression events via historical and recent interspecific hybridizations among six Chinese <it>Lepus </it>species. Remarkably, the mtDNA of <it>L. mandshuricus </it>was completely replaced by mtDNA from <it>L. timidus </it>and <it>L. sinensis</it>. Analysis of the nuclear DNA sequence revealed a high proportion of heterozygous genotypes containing alleles from two divergent clades and that several haplotypes were shared among species, suggesting repeated and recent introgression. Furthermore, results from the present analyses suggest that Chinese hares belong to eight species.</p> <p>Conclusion</p> <p>This study provides a framework for understanding the patterns of speciation and the taxonomy of this clade. The existence of morphological intermediates and atypical mitochondrial gene genealogies resulting from frequent hybridization events likely contribute to the current taxonomic confusion of Chinese hares. The present study also demonstrated that nuclear gene sequence could offer a powerful complementary data set with mtDNA in tracing a complete evolutionary history of recently diverged species.</p

Dwindling genetic diversity in European ground squirrels?

The European ground squirrel (Spermophilus citellus) is endangered and in decline. Populations are increasingly fragmented, and only a coordinated conservation effort at the European level may guarantee its long-term survival. To obtain a general population genetic picture on a larger geographic scale, we screened 117 individuals from seven local populations in Hungary, Romania, and Austria for allelic variation at eleven microsatellite loci. We found a high (23.4%) proportion of private alleles, and a moderate to somewhat elevated level (15.27%) of partitioning of genetic diversity among populations, compared to that found in many other terrestrial mammals. Genetic variability was significantly higher than in earlier studied Czech populations that are considered genetically depleted, but significantly lower than in undisturbed populations of S. suslicus and S. brunneus, that are similar to the European ground squirrel in their ecological requirements, reproductive biology, and social organization. Genetic diversity was also lower than in most presumably "undisturbed" populations of other Sciurid species. This, together with the observed level and pattern of genetic differentiation among populations, such as no significant increase of genetic differentiation with geographic distance and similar variance of genetic differentiation between populations independent of geographic distance, indicated the prevalence of relatively strong drift effects for all populations. A Bayesian STRUCTURE analysis and a factorial correspondence analysis concordantly revealed a fairly complex genetic composition of local populations, but no major geographic trend in the pattern of the genetic composition. Overall, the results suggest disintegration of local colonies that might earlier have been more connected genetically. The STRUCTURE analysis also suggested anthropogenic translocations among single Hungarian populations. Our data on genetic diversity and its distribution do not object to such conservation measures. Translocation of individuals particularly from nearby populations may increase the chances of survival of small and isolated populations and counteract inbreeding at low densities. (C) 2011 Deutsche Gesellschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved

Characterisation of the EM disturbances affecting the safety of the railway communication systems

To insure interoperability of transeuropean trains, new transmission systems (GSMR, Eurobalise) are developed in order to permit communications between trains and control centres. These systems have to be available and safe from an electromagnetic point of view, but the normalized methods to characterize electromagnetic noise in the railway environment are not convenient for these applications. This paper presents new experimental methods to characterize the electromagnetic noise on board trains which are studied in the framework of the European project “Railcom”. The results of measurements realized both in time and in frequency domains, are analysed and certain conclusions can be used as a first step to define a new standard for the considered systems

Population genetics of cape and brown hares (Lepus capensis and L. europaeus): A test of Petter's hypothesis of conspecificity

Phylogenetic relationships and systematics of hares and jackrabbits (genus Lepus, Lagomorpha) are notoriously difficult. One intriguing issue is the relationship between cape hares (Lepus capensis L., 1758) and brown hares (Lepus europaeus Pallas, 1778). According to Petter, F., [1959. Eléments d'une révision des lièvres africains du sous-genre Lepus. Mammalia 23, 41-67; 1961. Eléments d'une révision des lièvres européens et asiatique du sous-genre Lepus. Z. Säugetierkd. 26, 30-40], these two phenotypically different taxa are conspecific. On the contrary, recent arguments were put forward to split African capensis into several species. Eleven variable microsatellite loci were used to determine the spatial genetic structure of African and South Israeli hares, currently considered cape hares, and European, Anatolian, and North Israeli hares, currently considered brown hares. Patterns of genetic differentiation of 294 hares collected at 18 locations from both species ranges were examined for accordance to the hypothesis of conspecificity or to the concept of two distinct species, the cape hare and the brown hare. Genetic variation was high (14.7 alleles/locus) and the distribution of alleles and genotypes was not homogeneous across the locations. Results from FST, RST, and GST ′-statistics including various AMOVA models, comparisons of private alleles with corresponding relative genetic differentiation between neighbouring populations, as well as absolute genetic differentiation patterns were by and large congruent. They all indicated that the degree of differentiation between populations belonging to the two different taxa was not higher than within the taxa. Partitioning of genetic diversity was congruent with a isolation-by-distance model, and this also suggested that the differentiation was due to geographic distances rather than the occurrence of two species-specific gene pools. Homoplasy likely had no or only a marginal effect on our results, as indicated by the standardized genetic distance GST ′ and the presence of differently fixed alleles between the South African cape hare and all European brown hare populations at the highly polymorphic Sol08 locus. The results are concordant with earlier multilocus allozyme and mtDNA RFLP data, but contrast with mtDNA sequence data published earlier, that suggest distinctly separate phylogenetic units in Africa, the Near East and Europe. Nevertheless, as concluded from the microsatellite data brown hares and African cape hares might be connected via the Near East by gene flow along a network of intergrading populations that have regionally distinct gene pools. © 2007 Elsevier Ltd. All rights reserved