Insertion polymorphism of retrotransposable elements in populations of the insular, endemic species Drosophila madeirensis

The insertion site numbers of the retrotransposable elements (TE) 412, gypsy and bilbo were determined in individuals of five distinct natural populations of the endemic species Drosophila madeirensis from the island of Madeira. The TE distributions were compared to those of the paleartic, widespread and phylogenetically closely related species, D. subobscura. In situ hybridization and Southern blots showed that in D. madeirensis the number of insertion sites ranged between 10 and 15, three and six, and 35 and 42 for elements 412, gypsy and bilbo, respectively. The corresponding values for D. subobscura were similar. Two of these elements, 412 and gypsy, had very few insertions in the heterochromatin, unlike bilbo, which displayed a high heterochromatic insertion number. The Southern band polymorphism was very high, leading to within-population variation of 97.2%, whatever the population and the TE concerned. Using the polymorphic TE insertion sites as markers to analyse population structure by AMOVA, adapted for RAPD (Randomly Amplified Polymorphic DNA) data, we found small but significant genetic differences between the populations on Madeira. This slight differentiation, coupled with similar copy numbers for each TE between populations, suggests that the D. madeirensis species consists of a single, only slightly subdivided population. These data also show that insular populations and endemic species of Drosophila can have as many copies of TEs as more widespread species.info:eu-repo/semantics/publishedVersio

Functional heterogeneity of the fucoxanthins and fucoxanthin-chlorophyll proteins in diatom cells revealed by their electrochromic response and fluorescence and linear dichroism spectra

In this work, by analyzing the electrochromic transient spectra, the 77 K fluorescence emission and excitation, as well as the linear dichroism (LD) and circular dichroism (CD) spectra of low-light (LL) and high-light (HL) grown Phaeodactylum tricornutum cells, we show that the fucoxanthins (Fx) and fucoxanthin-chlorophyll proteins (FCP) exhibit marked functional heterogeneity. Electrochromic transients reveal that LL and HL cells differ substantially in their relative contents of two Fx forms, which absorb at 501 and 550 nm; they exhibit distinct LD signals but are CD silent. Fluorescence emission and excitation spectra at 77 K reveal that although both forms efficiently transfer excitation energy to Chl a, the red form feeds somewhat more energy to photosystem II than to photosystem I. Similar data obtained in Cyclotella meneghiniana cells suggest that the heterogeneity of the FCP pool, with different Fx forms, plays a role in the regulation of energy utilization in FCP-containing organisms. © 2010 Elsevier B.V. All rights reserved

Structurally flexible macro-organization of the pigment-protein complexes of the diatom Phaeodactylum tricornutum

By means of circular dichroism (CD) spectroscopy, we have characterized the organization of the photosynthetic complexes of the diatom Phaeodactylum tricornutum at different levels of structural complexity: in intact cells, isolated thylakoid membranes and purified fucoxanthin chlorophyll protein (FCP) complexes. We found that the CD spectrum of whole cells was dominated by a large band at (+)698 nm, accompanied by a long tail from differential scattering, features typical for psi-type (polymerization or salt-induced) CD. The CD spectrum additionally contained intense (-)679 nm, (+)445 nm and (-)470 nm bands, which were also present in isolated thylakoid membranes and FCPs. While the latter two bands were evidently produced by excitonic interactions, the nature of the (-)679 nm band remained unclear. Electrochromic absorbance changes also revealed the existence of a CD-silent long-wavelength (∼545 nm) absorbing fucoxanthin molecule with very high sensitivity to the transmembrane electrical field. In intact cells the main CD band at (+)698 nm appeared to be associated with the multilamellar organization of the thylakoid membranes. It was sensitive to the osmotic pressure and was selectively diminished at elevated temperatures and was capable of undergoing light-induced reversible changes. In isolated thylakoid membranes, the psi-type CD band, which was lost during the isolation procedure, could be partially restored by addition of Mg-ions, along with the maximum quantum yield and the non-photochemical quenching of singlet excited chlorophyll a, measured by fluorescence transients. © 2007 Springer Science+Business Media B.V

Phonons in the multiferroic langasite Ba_3\_3NbFe_3\_3Si_2\_2O_14\_{14} : evidences for symmetry breaking

The chiral langasite Ba$\_3$NbFe$\_3$Si$\_2$O$\_{14}$ is a multiferroic compound. While its magnetic order below T$\_N$=27 K is now well characterised, its polar order is still controversial. We thus looked at the phonon spectrum and its temperature dependence to unravel possible crystal symmetry breaking. We combined optical measurements (both infrared and Raman spectroscopy) with ab initio calculations and show that signatures of a polar state are clearly present in the phonon spectrum even at room temperature. An additional symmetry lowering occurs below 120~K as seen from emergence of softer phonon modes in the THz range. These results confirm the multiferroic nature of this langasite and open new routes to understand the origin of the polar state

Leading interactions in the β\beta-SrV6O15Sr V_6 O_{15} compound

The present study shows that the electronic structure of the $\beta$-$AV\_6O\_{15}$ family of compounds ($A = Sr, Ca, Na ...$) is based on weakly interacting two-leg ladders, in contrast with the zig-zag chain model one could expect from their crystal structure. Spin dimer analysis, based on extended H\"{u}ckel tight-binding calculations, was performed to determine the structure of the dominant transfer and magnetic interactions in the room temperature $\beta$-$SrV\_6O\_{15}$ phase. Two different two-legs ladders, associated with different charge/spin orders are proposed to describe these one-dimensional $\beta$-type systems. The antiferromagnetic ladders are packed in an 'IPN' geometry and coupled to each other through weak antiferromagnetic interactions. This arrangement of the dominant interactions explains the otherwise surprising similarities of the optical conductivity and Raman spectra for the one-dimensional $\beta$-type phases and the two-dimensional $\alpha$-type ones such as the well-known $\alpha^\prime$-$NaV\_2O\_5$ system

Elastic and magnetic effects on the infrared phonon spectra of MnF2

We measured the temperature dependent infrared reflectivity spectra of MnF2 between 4 K and room temperature. We show that the phonon spectrum undergoes a strong renormalization at TN. The ab-initio calculation we performed on this compound accurately predict the magnitude and the direction of the phonon parameters changes across the antiferromagnetic transition, showing that they are mainly induced by the magnetic order. In this material, we found that the dielectric constant is mostly from phonon origin. The large change in the lattice parameters with temperature seen by X-ray diffraction as well as the A2u phonon softening below TN indicate that magnetic order induced distortions in MnF2 are compatible with the ferroelectric instabilities observed in TiO2, FeF2 and other rutile-type fluorides. This study also shows the anomalous temperature evolution of the lower energy Eu mode in the paramagnetic phase, which can be compared to that of the B1g one seen by Raman spectroscopy in many isostructural materials. This was interpreted as being a precursor of a phase transition from rutile to CaCl2 structure which was observed under pressure in ZnF2.Comment: 8 pages, 8 figures, updated version accepted in PR

Real-time landing place assessment in man-made environments

We propose a novel approach to the real-time landing site detection and assessment in unconstrained man-made environments using passive sensors. Because this task must be performed in a few seconds or less, existing methods are often limited to simple local intensity and edge variation cues. By contrast, we show how to efficiently take into account the potential sites' global shape, which is a critical cue in man-made scenes. Our method relies on a new segmentation algorithm and shape regularity measure to look for polygonal regions in video sequences. In this way, we enforce both temporal consistency and geometric regularity, resulting in very reliable and consistent detections. We demonstrate our approach for the detection of landable sites such as rural fields, building rooftops and runways from color and infrared monocular sequences significantly outperforming the state-of-the-art

Quantitative parameters for the examination of InGaN QW multilayers by low-loss EELS

We present a detailed examination of a multiple InxGa1-xN quantum well (QW) structure for optoelectronic applications. The characterization is carried out using scanning transmission electron microscopy (STEM), combining high-angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS). Fluctuations in the QW thickness and composition are observed in atomic resolution images. The impact of these small changes on the electronic properties of the semiconductor material is measured through spatially localized low-loss EELS, obtaining band gap and plasmon energy values. Because of the small size of the InGaN QW layers additional effects hinder the analysis. Hence, additional parameters were explored, which can be assessed using the same EELS data and give further information. For instance, plasmon width was studied using a model-based fit approach to the plasmon peak; observing a broadening of this peak can be related to the chemical and structural inhomogeneity in the InGaN QW layers. Additionally, Kramers-Kronig analysis (KKA) was used to calculate the complex dielectric function (CDF) from the EELS spectrum images (SIs). After this analysis, the electron effective mass and the sample absolute thickness were obtained, and an alternative method for the assessment of plasmon energy was demonstrated. Also after KKA, the normalization of the energy-loss spectrum allows us to analyze the Ga 3d transition, which provides additional chemical information at great spatial resolution. Each one of these methods is presented in this work together with a critical discussion of their advantages and drawbacks

Transition State Spectroscopy of the Photoinduced Ca + CH3F Reaction. 2. Experimental and Ab Initio Studies of the Free Ca***FCH3 Complex

International audienceThe Ca* + CH3F CaF* + CH3 reaction was photoinduced in 1:1 Ca***CH3F complexes formed in a supersonic expansion. The transition state of the reaction was explored by monitoring the electronically excited product, CaF, while scanning the laser that turns on the reaction. Moreover, the electronic structure of the Ca***FCH3 system was studied using ab initio methods by associating a pseudopotential description of the [Ca2+] and [F7+] cores, a core polarization operator on calcium, an extensive Gaussian basis and a treatment of the electronic problem at the CCSD(T) (ground state) and RSPT2 (excited states) level. In this contribution we present experimental results for the free complex and a comparison with the results of a previous experiment where the Ca***CH3F complexes are deposited at the surface of large argon clusters. The ab initio calculations allowed an interpretation of the experimental data in terms of two reaction mechanisms, one involving a partial charge transfer state, the other involving the excitation of the C-F stretch in the CH3F moiety prior to charge transfer