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S Grenier

Publications and source records attributed to S Grenier.

14 recordsLinked to original sources
PubMed2005

d-d excitations in manganites probed by resonant inelastic x-ray scattering.

We report a study of electronic excitations in manganites exhibiting a range of ground states, using resonant inelastic x-ray scattering (RIXS) at the Mn K edge. Excitations with temperature dependent changes correlated with the magnetism were observed as high as 10 eV. By calculating Wannier functions, and finite-q response functions, we associate this dependence with intersite d-d excitations. The calculated dynamical structure factor is found to be similar to the RIXS spectra.

Journal Article↗
PubMed2004

Soft x-ray resonant diffraction study of magnetic and orbital correlations in a manganite near half doping.

We have utilized resonant x-ray diffraction at the Mn L(II,III) edges in order to directly compare magnetic and orbital correlations in Pr0.6Ca0.4MnO3. Comparing the widths of the magnetic and orbital diffraction peaks, we find that the magnetic correlation length exceeds that of the orbital order by nearly a factor of 2. Furthermore, we observe a large (approximately 3 eV) spectral weight shift between the magnetic and orbital resonant line shapes, which cannot be explained within the classic Goodenough picture of a charge-ordered ground state. To explain the shift, we calculate the orbital and magnetic resonant diffraction line shapes based on a relaxed charge-ordered model.

Journal Article↗
PubMed2003

Diffraction anomalous fine-structure spectroscopy at beamline BM2 at the European Synchrotron Radiation Facility.

Diffraction anomalous fine-structure (DAFS) spectroscopy uses resonant elastic X-rays scattering as an atomic, shell and site-selective probe that provides information on the electronic structure and the local atomic environment as well as on the long-range-ordered crystallographic structure. A DAFS experiment consists of measuring the Bragg peak intensities as a function of the energy of the incoming X-ray beam. The French CRG (Collaborative Research Group) beamline BM2-D2AM (Diffraction Diffusion Anomale Multi-longueurs d'Onde) at the ESRF (European Synchrotron Radiation Facility) has developed a state-of-the-art energy scan diffraction set-up. In this article the requirements for obtaining reliable DAFS data are presented and recent technical achievements are reported.

Algorithms↗
PubMed2001

Probing the transducin nucleotide binding site with GDP analogues.

An affinity study between the G protein of the visual photoreceptor, transducin, and eight different non-hydrolyzable GDP analogues is described. Imidodiphosphate derivatives have been shown to exhibit good affinities to transducin. This very important heterotrimeric G protein is shown to be highly restrictive with regard to structural modifications of the nucleotide at the pyrophosphate moiety, at the 3' position on ribose, as well as at the N1 position of the purine.

Binding Sites↗
PubMed2001

Glancing-angle diffraction anomalous fine structure of InAs quantum dots and quantum wires.

We have performed Diffraction Anomalous Fine Structure measurements at the As K-edge of self-growth InAs/InP(001) Quantum Wires and InAs/GaAs(001) Quantum Dots. The samples have been grown by Molecular Beam Epitaxy and their equivalent thickness is of 2.5 monolayers. We have measured the (440) and (420) Bragg reflections in glancing-angle scattering geometry, at incidence angles close to the substrate critical angle. We demonstrate the feasibility of the experiment reporting, for the first time. Diffraction Anomalous Fine Structure spectra of such low coverage epitaxial layers, and we show that the analysis of the Diffraction Anomalous Fine Structure lineshape together with the analysis of oscillatory part of the signal, can provide information about composition and strain of the nanostructures.

Journal Article↗
PubMed2001

Valence selective DAFS measurements of Mn in La1/3Ca2/3MnO3.

The manganese perovskite system La(1-x)Ca(x)MnO3 displays a complex phase diagram of structural, magnetic, and transport properties with varying Ca concentration. At x = 2/3 and at low temperature, the system is antiferromagnetic with Mn4+ and Mn3+ ions occupying special positions in a charge-ordered supperlattice. The charge ordering transition at about 260 K is characterized by the appearance of satellite peaks around certain strong normal lattice reflections. The normal lattice reflections are due to scattering from planes containing Mn4+ and Mn3+ ions in nearly stoichiometric proportion, however the superlattice reflections are due to scattering from planes containing only Mn4+ ions. By measuring Diffraction Anomalous Fine-Structure spectral on a superlattice reflection and its associated normal lattice reflection, it is possible to isolate absorption-like spectra for the two Mn sites. Due to the weak intensity of these superlattice reflections, we were unable to obtain high quality near-edge spectra for the superlattice reflection measured. However, the data offer useful information about the local electronic structures of the two Mn ions.

Journal Article↗
PubMed2001

A Fe(x)Mn1-x/Ir(001) multilayer probed by EXAFS and DAFS.

Diffraction Anomalous Fine Structure (DAFS) and EXAFS measurements have been performed on a (Fe0.7Mn0.3)/Ir(100)40 super-lattice at the K-edges of Fe and Mn. Theoretical EXAFS spectra have been refined: a slight difference in the first neighbor distance suggests a non homogeneous distribution of the Mn in the alloy. The smooth features of the DAFS spectra have been modeled to study the composition and the strain profile along the growth axis.

Journal Article↗
PubMed2000

Dynamics of Wolbachia populations in transfected lines of Trichogramma.

Fluorescence in situ hybridization was tested to specifically detect symbionts of the genus Wolbachia in Trichogramma and to allow for semiquantitative estimations of symbiont abundance. Extraction solutions used for horizontal transfers of symbionts contain a high abundance of Wolbachia, but Wolbachia have a low and decreasing abundance in microinjected lines (transfected lines). Moreover, eggs of microinjected lines were shown to be polymorphic for the infection. In naturally infected lines, Wolbachia are localized at the posterior pole of the eggs; they are scattered during the early stages of larval development and then concentrated in the ovaries at the end of the female pupal development. Scattering and concentration are probably not active but rather the result of replications or morphogenesis. Conversely, Wolbachia are not concentrated at the posterior pole of eggs in microinjected lines. Comparison of the within-family and between-family variances of the symbiont abundance in a microinjected line did not lead us to conclude that this character shows a genetic variability.

Animals↗
PubMed2000

Addition of wsp sequences to the Wolbachia phylogenetic tree and stability of the classification.

Wolbachia are symbiotic bacteria altering reproductive characters of numerous arthropods. Their most recent phylogeny and classification are based on sequences of the wsp gene. We sequenced wsp gene from six Wolbachia strains infecting six Trichogramma species that live as egg parasitoids on many insects. This allows us to test the effect of the addition of sequences on the Wolbachia phylogeny and to check the classification of Wolbachia infecting Trichogramma. The six Wolbachia studied are classified in the B supergroup. They confirm the monophyletic structure of the B Wolbachia in Trichogramma but introduce small differences in the Wolbachia classification. Modifications include the definition of a new group, Sem, for Wolbachia of T. semblidis and the merging of the two closely related groups, Sib and Kay. Specific primers were determined and tested for the Sem group.

Animals↗
PubMed1998

Determination of the depth of penetration of the alpha subunit of retinal G protein in membranes: a spectroscopic study.

This paper reports the fluorescence quenching of the alpha subunit of retinal rod outer segment G protein (Gtalpha) by vesicles of brominated phospholipids. Two different brominated phospholipids with the bromine quencher groups attached at the 6-7 and 9-10 positions in one of the fatty acyl chains have been used to estimate the depth of penetration of the Gtalpha protein in the lipid vesicles using steady-state fluorescence quenching techniques. Our studies provide evidence of the interaction between Gtalpha protein, in its active conformation, with the lipid vesicles mimicking natural membranes. This study demonstrates that in vitro the distance between fluorescent tryptophan site of Gtalpha and the membrane surface is approximately 6.5 A.

Animals↗
PubMed1982

[Dynamics of egg maturation in the parasitoid Lixophaga diatraeae (Diptera, Tachinidae) raised in a substitute host, Galleria mellonella (Lepidoptera, Pyralidae)].

The content of the uterus and ovaries of L. diatraeae (an ovolarviparous tachinid fly) was studied by dissecting 121 females 0 to 25 days old. Several size classes of flies (p: small; m: medium; g: big) were used, weighing 10 to 12.5 mg, 12.5 to 13.5 mg, and 13.5 to 16 mg, respectively. The mean number of ovarioles per ovary, correlated to female size, was 12.1 for p as against 12.9 for m + g females. The total mean number of eggs and oocytes changed with female age and weight. For 0, 5, 10 and 15-day old females, this number was 56, 149, 158 and 202, respectively in g flies and 51, 128, 141 and 139, respectively, in p ones. To study egg maturation dynamics, we counted the total number of eggs + oocytes per p female (Y1), the eggs in the uterus (Y2), partially embryonated eggs (Y3), and entirely embryonated eggs (Y4). The experimental results were fitted to various age functions using a non-linear adjustment program. The models fitting each datum best were asymptotic functions of the form, Y = A [1-e-K(x-D)], where A is the asymptotic value, K a speed constant of the studied phenomenon and D age at the beginning of the phenomenon. At emergence time, each female contained a mean of 50 oocytes which passed into the uterus immediately after mating. Egg production continued for at least 10 days after emergence. The rate of embryogenesis seemed to be influenced by the number of eggs in the uterus and/or the age of the fly; it was high for the first eggs then decreased progressively. In our conditions, the first eggs with a planidium ready to hatch appeared at 10 days post-emergence. To obtain a maximum number of larvae in good health, it is better to dissect 12 to 18-day old females. The egg volume increases slightly during embryogenesis.

Animals↗