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Early Middle Paleozoic Intraplate Orogeny in the Ogcheon Belt (South Korea): A new insight on the Paleozoic buildup of east Asia

Laurent Jolivet est Professeur à l'Université d'Orléans depuis le 1er septembre 2009.International audienceThe polycyclic Ogcheon belt of South Korea represents the boundary between two Precambrian blocks. Investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the Asian continent. We report here structural evidence showing that the earlier tectonic event dates back to early middle Paleozoic (the "Ogcheon tectonism" or "orogeny"). The ductile piling up of nappes of the Ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area. The nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement. Field evidence includes the presence of S1 and S1-2 foliations bearing an extensive stretching lineation perpendicular to the belt, associated with a strongly noncoaxial deformation regime. The F1 isoclinal folds are commonly "A type" and sheath folds whose axes are parallel to the stretching lineation, whereas the southeast facing F2 recumbent folds have subhorizontal axes parallel to the belt. All lines of evidence (unconformity, superposed deformations, age of the metamorphism, etc...) imply that the D1-2 "Ogcheon tectonism" is pre-middle Carboniferous (Late Silurian-Early Devonian). The subsequent Indosinian (Middle Triassic) F3 upright synfolial folds that trend NNE-SSW and later structures clearly overprint the middle Paleozoic ductile thrusts and isoclinal folds. The early Paleozoic Ogcheon Supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin. On the basis of the geochemical characteristics of the metavolcanics, it appears that oceanization did not occur and Ogcheon rift aborted soon after it was formed. We suggest that middle Paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features. During the ductile stacking episode, the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event. Middle Carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks. A tentative correlation with early Paleozoic Imjingang, Qinling and Cathaysian belts within the Asian continent reveals that Ogcheon rift was emplaced within the South China plate and that Imjingang belt should represent the limit between North and South China blocks in the Korean peninsula

Imagerie hyperspectrale en champ proche optique (développement et applications à la nanophotonique)

La microscopie en champ proche optique permet d'analyser les phénomènes optiques avec une résolution spatiale sublongueur d'onde comme par exemple la localisation et la propagation de la lumière dans des cristaux photoniques. D'une manière générale, les méthodes de microscopie en champ proche optique reposent sur le positionnement à l'échelle nanométrique d'une sonde locale à proximité de l'échantillon à analyser, puis sur la détection du signal diffusé et collecté lors du balayage de la sonde. En fonction du type de détection optique mise en oeuvre ou du type de sonde utilisée, les grandeurs physiques communément accessibles par ces méthodes sont les distributions spatiales de l'amplitude et de la phase ou de l'intensité des composantes électriques ou magnétiques du champ sondé.Ce travail de thèse est consacré à la mise en place d'une détection hyperstectrale en champ proche optique dans le but de comprendre et de caractériser, à des échelles sublongueurs d'onde, les propriétés spectrales et spatiales de systèmes optiques miniaturisés. L'imagerie hyperstectrale fournit en une seule acquisition, une série d'image à chaque longueur d'onde dans les gammes spectrales visibles, infrarouges et aux longueurs d'onde des télécommunications optiques. Cette nouvelle technique d'imagerie a permis l'observation, sur une large bande spectrale, de phénomènes électromagnétiques dépendant de la longueur d'onde tels que les effets superprisme et mirage dans les cristaux photoniques et la mise en forme de faisceaux de Bessel plasmoniquesThe scanning near-field optical microscopy (SNOM) is used to analyze optical phenomena at the sub-wavelength scale such as light localization and propagation in photonic crystals or plasmonic devices. In any case, SNOM experiments rely on the positioning of a local probe in the optical near field of a given structure and on the detection of the surrounding evanescent waves. Depending on the nature of the probe or on the optical detection method, the detected physical properties are the spatial distributions of the amplitude and phase or the intensity of the electric and magnetic components of the probed field. We present here the implementation of an innovative hyperspectral near-field imaging method which aims to detect both spectral and spatial properties of an optical nanosystem at the subwavelength scale. The presented method provides a batch of images over a broad spectral range at visible; near-infrared and telecommunication wavelengths. Using this technique, we report here the near-field observations through the spectrum of the emblematic electromagnetic phenomena involved in photonic crystals and plasmonics such as light waveguiding, trapping or beam shapingDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

First Triassic palaeomagnetic constraints from Junggar (NW China) and their implications for the Mesozoic tectonics in Central Asia

International audienceNorthwestern China belts result from the Palaeozoic collage of Central Asia and the subsequent reactivations due to far-field effects of the Mesozoic Tibetan and the Cenozoic Himalayan collisions. Triassic is a crucial period to understand and decipher the tectonics related to these two episodes. About 250 oriented palaeomagnetic cores from 43 sites were collected from six sections of Upper Permian to Late Triassic sandstone, in South and West Junggar, Northwestern China. Thermomagnetic, IRM and hysteresis measurements reveal magnetite as the main carrier of the magnetic remanence with minor hematite and maghemite. Stepwise thermal demagnetisation has generally isolated two components. The low temperature component, up to 300-350 °C, displays a direction consistent with the present-day geomagnetic field. The locality-mean directions related to the high temperature component (above 350 °C) were also calculated. Two out of six sections display intense viscous magnetisation and the occurrence of maghemite reveals a possible Cenozoic chemical remagnetisation for these two localities. For the other four localities, we assume that the magnetisation is primary because: (1) AMS measurements reveal a primary fabric, (2) there are local occurrences of antipodal polarities, and (3) palaeolatitudes of tilt-corrected poles are compatible with previous studies. The consistency between the Early Triassic poles of West and South Junggar indicates that Junggar evolved as a rigid block only since Early Mesozoic. The comparison of the Late Palaeozoic and the Early Mesozoic poles of Junggar and those of Siberia and Tarim shows major rotations between the Late Permian and the Late Jurassic-Early Cretaceous. These periods of discrete rotations are characterized by strike-slip faulting in Tianshan and Altai and they may correlate with the major episodes of coarse-grained detrital sedimentation and uplift of the range. Especially, the counter-clockwise rotations of Junggar relative to Tarim and Siberia, which occurred between the Early and the Late Triassic and between the Late Triassic and the Late Jurassic, are accommodated by transpressive tectonics in the Tianshan and the Altai belts. This reactivation is a far-field effect of Tibetan blocks diachronous collisions. Therefore, these first Triassic palaeomagnetic results from Junggar infer that post-Carboniferous rotations were due to the combined effect of the post-orogenic transcurrent movement and the Mesozoic oblique reactivation

Transmission du patrimoine architectural au Japon : décryptage

Les questions relatives à la transmission du patrimoine architectural ont fait l’objet de nombreux débats dans les années 1990. Les voix de Françoise Choay, Alain Schnapp, André Chastel, Pierre Nora ont particulièrement marqué ces échanges. Concentrés sur les civilisations européennes, voire méditerranéennes, tous se sont intéressés à la diversité des approches en matière de transmission patrimoniale et, en cherchant un envers aux pratiques occidentales, tous ont été interpelés par la pratiqu..

Near-field interactions between a subwavelength tip and a small-volume photonic-crystal nanocavity

International audienceThe fundamentals of the near-field interaction between a subwavelength metallic tip and a photonic-crystal nanocavity are investigated experimentally and theoretically. It is shown experimentally that the cavity resonance is tuned without any degradation by the presence of the tip and that the reported near-field interaction is strongly related to the field distribution within the nanostructure. Then, in light of a perturbation theory, we show that this interaction is selectively related to the electric field or magnetic field distribution within the cavity, depending on the tip properties

Generation of Two-Dimensional Plasmonic Bottle Beams

By analogy to the three dimensional optical bottle beam, we introduce the plasmonic bottle beam: a two dimensional surface wave which features a lattice of plasmonic bottles, i.e. alternating regions of bright focii surrounded by low intensities. The two-dimensional bottle beam is created by the interference of a non-diffracting beam, a cosine-Gaussian beam, and a plane wave, thus giving rise to a non-diffracting complex intensity distribution. By controlling the propagation constant of the cosine-Gauss beam, the size and number of plasmonic bottles can be engineered. The two dimensional lattice of hot spots formed by this new plasmonic wave could have applications in plasmonic trapping.Engineering and Applied Science

The Tyrosine-Autokinase UbK Is Required for Proper Cell Growth and Cell Morphology of Streptococcus pneumoniae

International audienceProtein phosphorylation is a key post-translational modification required for many cellular functions of the bacterial cell. Recently, we identified a new protein-kinase, named UbK, in Bacillus subtilis that belongs to a new family of protein-kinases widespread in bacteria. In this study, we analyze the function of UbK in Streptococcus pneumoniae. We show that UbK displays a tyrosine-kinase activity and autophosphorylates on a unique tyrosine in vivo. To get insights into its cellular role, we constructed a set of pneumococcal ubk mutants. Using conventional and electron microscopy, we show that the ubk deficient strain, as well as an ubk catalytic dead mutant, display both severe cell-growth and cell-morphology defects. The same defects are observed with a mutant mimicking permanent phosphorylation of UbK whereas they are not detected for a mutant mimicking defective autophosphorylation of UbK. Moreover, we find that UbK phosphorylation promotes its ability to hydrolyze ATP. These observations show that the hydrolysis of ATP by UbK serves not only for its autophosphorylation but also for a distinct purpose essential for the optimal cell growth and cell-morphogenesis of the pneumococcus. We thus propose a model in which the autophosphorylation/dephosphorylation of UbK regulates its cellular function through a negative feedback loop

Excluded volume effects on the structure of a linear polymer under shear flow

The effect of excluded volume interactions on the structure of a polymer in shear flow is investigated by Brownian Dynamics simulations for chains with size $30\leq N\leq 300$. The main results concern the structure factor $S({\bf q})$ of chains of N=300 Kuhn segments, observed at a reduced shear rate $\beta=\dot{\gamma}\tau=3.2$, where $\dot{\gamma}$ is the bare shear rate and $\tau$ is the longest relaxation time of the chain. At low q, where anisotropic global deformation is probed, the chain form factor is shown to match the form factor of the continuous Rouse model under shear at the same reduced shear rate, computed here for the first time in a wide range of wave vectors. At high q, the chain structure factor evolves towards the isotropic equilibrium power law $q^{-1/\nu}$ typical of self-avoiding walk statistics. The matching between excluded volume and ideal chains at small q, and the excluded volume power law behavior at large q are observed for ${\bf q}$ orthogonal to the main elongation axis but not yet for ${\bf q}$ along the elongation direction itself, as a result of interferences with finite extensibility effects. Our simulations support the existence of anisotropic shear blobs for polymers in good solvent under shear flow for $\beta>1$ provided chains are sufficiently long.Comment: 36 pages, 11 figures, submitted to J. Chem. Phy