Newinsights in the ontogeny and taphonomy of the Devonian acanthodian Triazeugacanthus affinis from the Miguasha Fossil-Lagerstatte, Eastern Canada

Progressive biomineralization of a skeleton occurs during ontogeny in most animals. In fishes, larvae are poorly mineralized, whereas juveniles and adults display a progressively more biomineralized skeleton. Fossil remains primarily consist of adult specimens because the fossilization of poorly-mineralized larvae and juveniles necessitates exceptional conditions. The Miguasha Fossil-Lagerstatte is renowned for its Late Devonian vertebrate fauna, revealing the exceptional preservation of fossilized ontogenies for 14 of the 20 fish species from this locality. The mineralization of anatomical structures of the acanthodian Triazeugacanthus affinis from Miguasha are compared among larval, juvenile and adult specimens using Energy Dispersive X-ray Spectrometry. Chemical composition of anatomical structures of Triazeugacanthus reveals differences between cartilage and bone. Although the histology and anatomy is well-preserved, Fourier transform infrared spectrometry shows that the original chemical composition of bone is altered by diagenesis; the mineral phase of the bone (i.e., hydroxyapatite) is modified chemically to form more stable carbonate-fluorapatite. Fluorination occurring in mineralized skeletal structures of adult Triazeugacanthus is indicative of exchanges between groundwater and skeleton at burial, whereas the preservation of larval soft tissues is likely owing to a rapid burial under anoxic conditions. The exceptional state of preservation of a fossilized ontogeny allowed us to characterize chemically the progressive mineralization of the skeleton in a Devonian early vertebrate

Multiple plasmon resonances in naturally-occurring multiwall nanotubes: infrared spectra of chrysotile asbestos

Chrysotile asbestos is formed by densely packed bundles of multiwall hollow nanotubes. Each wall in the nanotubes is a cylindrically wrapped layer of $Mg_3 Si_2 O_5 (OH)_4$. We show by experiment and theory that the infrared spectrum of chrysotile presents multiple plasmon resonances in the Si-O stretching bands. These collective charge excitations are universal features of the nanotubes that are obtained by cylindrically wrapping an anisotropic material. The multiple plasmons can be observed if the width of the resonances is sufficiently small as in chrysotile.Comment: 4 pages, 5 figures. Revtex4 compuscript. Misprint in Eq.(6) correcte

Анаэробные неклостридиальные флегмоны таза: современный взгляд на проблемы хирургического лечения

Проанализированы современные литературные источники по проблеме хирургического лечения анаэробных неклостридиальных флегмон таза, выявлены дискуссионные и требующие дальнейшего изучения вопросы как оперативного, так и послеоперационного местного лечения патологического процесса.Проаналізовано сучасні літературні джерела з проблеми хірургічного лікування анаеробних неклостридіальних флегмон тазу, виявлено дискусійні питання як оперативного, так і післяопераційного місцевого лікування патологічного процесу, що потребують подальшого вивчення.Contemporary literature on the problem of surgical treatment of anaerobic nonclostridial cellulitis of the pelvis was analyzed. Disputable questions and those requiring research concerning both operative and postoperative topical treatment of the pathological process were revealed

RAPD-анализ клеточных линий сои с перекрестной устойчивостью к оксианионам вольфрама и ванадия

Исследовали влияние оксианионов ванадия на геном сои (Glycine max L., Merr.) в устойчивой к вольфраму (WR) клеточной линии. WR-линия показывает перекрестную устойчивость к оксианионам V⁵⁺. Установлено наличие одинаковых по размеру RAPD-ампликонов, дифференциально синтезируемых с ДНК исходного каллуса и WR-линии, которая последовательно культивируется в присутствии летальных доз оксианионов W⁶⁺ и V⁵⁺. Предположено, что в геноме сои имеются локусы, повышенная нестабильность которых обусловлена действием разных стрессоров.Вивчали вплив оксианіонів ванадію на геном сої (Glycine max L., Merr.) у стійкої до вольфраму (WR) клітинної лінії. Така лінія показує стійкість до оксианіонів V⁵⁺. Встановлено наявність однакових за розміром RAPD-ампліконів, які диференційно синтезуються з ДНК вихідного калюсу та WR-лінії, що послідовно культивується у присутності летальних доз оксианіонів W⁶⁺ і V⁵⁺. Припущено, що в геномі сої є локуси, підвищена нестабільність яких обумовлена дією різних стресорів.The effect of vanadium oxyanions on genome of soybean (Glycine max L., Merr.) in tungsten-resistant cell line was studied. The line is resistant to V⁵⁺-oxyanions. RAPD-amplicons with identical length are differentially synthesized from DNAs of tungsten-resistant cell line as well as of the initial culture was shown by using the lethal dose of oxyanions W⁶⁺ and then V⁵⁺. The presence of instable loci in soybean genome under different stressors is discussed

X-ray Linear Dichroism in cubic compounds: the case of Cr3+ in MgAl2O4

The angular dependence (x-ray linear dichroism) of the Cr K pre-edge in MgAl2O4:Cr3+ spinel is measured by means of x-ray absorption near edge structure spectroscopy (XANES) and compared to calculations based on density functional theory (DFT) and ligand field multiplet theory (LFM). We also present an efficient method, based on symmetry considerations, to compute the dichroism of the cubic crystal starting from the dichroism of a single substitutional site. DFT shows that the electric dipole transitions do not contribute to the features visible in the pre-edge and provides a clear vision of the assignment of the 1s-->3d transitions. However, DFT is unable to reproduce quantitatively the angular dependence of the pre-edge, which is, on the other side, well reproduced by LFM calculations. The most relevant factors determining the dichroism of Cr K pre-edge are identified as the site distortion and 3d-3d electronic repulsion. From this combined DFT, LFM approach is concluded that when the pre-edge features are more intense than 4 % of the edge jump, pure quadrupole transitions cannot explain alone the origin of the pre-edge. Finally, the shape of the dichroic signal is more sensitive than the isotropic spectrum to the trigonal distortion of the substitutional site. This suggests the possibility to obtain quantitative information on site distortion from the x-ray linear dichroism by performing angular dependent measurements on single crystals

Theoretical infrared spectra of OH defects in corundum (α-Al2O3)

International audienceThe atomic-scale structure, relative stability and infrared spectroscopic properties of OH defects in corundum (α-Al 2 O 3) are theoretically investigated at the density functional theory level. Comparison with experimental data makes it possible to assign most of the narrow bands observed between 3150 and 3400 cm −1 in natural and Ti-or V-doped synthetic corundum to specific defects. These defects correspond to the association of one OH group with an Al vacancy and M 4+ for Al 3+ substitutions in neighboring sites. The OH group is located in the large oxygen triangle forming the base of the vacant Al site. Models of interstitial proton associated with a nearby Mg 2+ for Al 3+ substitution are consistent with the broad band observed at 3010 cm −1 in Mg-doped corundum. Its is also suggested that two weaker OH-stretching bands observed in nominally pure synthetic corundum at 3163 and 3209 cm −1 could be associated with intrinsic defects combining an Al and an O vacancy. These results highlight the importance of defect clustering in the high-temperature incorporation of hydrogen in nominally anhydrous minerals

Structural Fe3+ in Natural Kaolinites: New Insights from Electron Paramagnetic Resonance Spectra Fitting at X and Q-Band Frequencies

International audienceStructural Fe 3+ in kaolinites and dickites covering a broad range of disorder was investigated using electron paramagnetic resonance (EPR) spectroscopy at both the X and Q-band frequencies. A procedure based on a numerical diagonalization of the spin Hamiltonian was used to accurately determine the second and fourth-order fine-structure parameters. A least-squares fitting method was also developed to model the EPR spectra of Fe 3+ ions in disordered local environments, including multimodal site-tosite distributions. Satisfactory fits between calculated and observed X and Q-band spectra were obtained regardless of the stacking order of the samples.In well-ordered kaolinite, Fe 3+ ions are equally substituted in sites of axial symmetry (Fe(ii)sites, namely Fe(m a and Fe(mb) which were determined to be the two non-equivalent All and A12 sites of the kaolinite structure. In dickite, Fe 3+ ions were also found to be equally substituted for AP + in the two non-equivalent A1 sites of the dickite structure. In poorly ordered kaolinites, the distribution of the fine-structure parameters indicates that Fe 3+ ions are distributed between Fe(,> sites and other sites with the symmetry of the dickite sites.Hence, when stacking disorder prevails over local perturbations of the structure, the near isotropic resonance owing to Fe 3+ ions in rhombically distorted sites (Fe(i) sites) is a diagnostic feature for the occurrence of C-layers in the kaolinite structure, where C refers to a specific distribution of vacant octahedral sites in successive layers

Cristallochimie des apatites biologiques et géologiques (marqueurs minéralogiques de la fossilisation)

Cette Thèse a pour but d étudier la cristallochimie des apatites, constituants majeurs des dents et des os des vertébrés, afin de discuter leur utilisation comme marqueurs de la fossilisation. Nous avons combiné des techniques expérimentales avancées (spectrométrie IR à basse température et RMN du solide) et des modélisations théoriques réalisées par des méthodes ab initio de type DFT. Le mécanisme de substitution des groupes carbonate aux groupes phosphate dans la "francolite" a pour la première fois été élucidé. L accord entre les résultats expérimentaux et leurs contreparties théoriques a permis de valider un modèle de substitution couplée où le carbonate occupe l'une des faces du site tétraédrique et le fluor le sommet opposé. Les propriétés spectrométriques spécifiques de ce défaut ont été déterminées et permettent son identification dans les échantillons naturels. D'autres modèles d'incorporation du carbonate ont également été étudiés et discutés à la lumière des résultats expérimentaux. Ces résultats ont ensuite été appliqués à l'étude de la transformation de fossiles de dents et d os. L'identification de l'environnement du carbonate de type "francolite" dans les échantillons d'émail de dents fossiles implique que celles-ci se transforment par dissolution-recristallisation. Cette observation est donc susceptible de remettre en cause l'utilisation des fossiles les plus transformés pour les reconstitutions paléo-environnementales. En comparaison, la fossilisation des os procède par un mécanisme plus complexe impliquant des réorganisations précoces de la structure phosphatée suivies à plus long terme par des remplacements par dissolution-recristallisationThis Thesis aims to study the crystal-chemistry of apatite, the main mineral constituent of vertebrate bones and teeth, in order to discuss its use as marker of fossilization. We have combined advanced experimental techniques (FTIR at low temperature and solid-state NMR MAS) and theoretical ab initio modelling carried out by DFT methods. The substitution mechanism of carbonate groups for phosphate groups in the sedimentary carbonate fluorapatite (francolite) has been for the first time elucidated. The agreement between experimental results and their theoretical counterparts allows validating a model of coupled substitution where carbonate occupies one face of the tetrahedral site and fluorine the opposite vertex. Specific spectroscopic properties of this defect have been determined and allow its identification in natural samples. Other models of carbonate incorporation have also been investigated and discussed under the light of experimental results. These results have been then applied to the study of the transformation of fossil teeth and bones. The identification of the "francolite-type carbonate defect in fossil tooth enamel implies that their transformation may occur through dissolution and recrystallization mechanisms. Our findings challenge the use of the most transformed fossils for paleoenvironmental reconstructions. In comparison, the fossil bones proceed by a complex mechanism involving early reorganization of the phosphate structure followed by longer-term replacements by dissolution-recrystallization mechanisms.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Theoretical OH stretching vibrations in dravite

International audienceDensity functional theory is used to investigate the vibrational stretching properties of OH groups in ideal and chemically disordered dravite models. Different schemes of cationic occupancy are considered, including the occurrence of vacancies at the X site and Mg–Al inversion between the Y and Z sites. The harmonic coupling between different OH groups is found to be smaller than 1 cm−1, indicating that the OH stretching dynamic in dravite can be described by considering a collection of nearly independent single OH oscillators. Their harmonic stretching frequency is linearly correlated with the corresponding OH bond length and most of the bands observed in the experimental vibrational spectra can be interpreted as consequences of the cationic occupancy of the sites coordinated to the OH group. The V(OH) and W(OH) stretching frequencies are affected by the Mg–Al inversion and by the presence of vacancies at the X site. In this last case, the frequencies depend on the isolated or more concentrated character of the X vacancy distribution along the c axis. Based on theoretical stretching frequencies, new interpretations are proposed for some of the bands experimentally observed in synthetic samples of dravite and magnesio-foitite