Éditeur(s) : HAL CCSD Coastal Education and Research Foundation, Inc.
Résumé : International audience
Morphodynamics of sandy, macrotidal, embayed beaches is complex because of the numerous physical processes interacting at the same location over a wide range of temporal scales. As most of these processes are controlled by beach morphology, dynamic feedbacks are generally observed between hydro- and morphodynamics. Investigating short-term processes is essential in order to improve long term morphological prediction. A key question is to understand how beach slope reacts to forcing conditions, in particular the response time of the beach profile, how long the transient state lasts. This study deals with the spatial and temporal responses of beach morphology to varying incident conditions. Here we report main observations, preliminary results and on-going investigations on the DYNATREZ1 field campaign, which was conducted in the framework of the National Observation Service Dynalit. Beach profiles are shown to adapt rapidly to forcing conditions, within two days, with more intense variations observed in the high tide swash zone. The presence of infragravity waves and their dissipation on the beach is highlighted. It is likely that the very large variability in beach slope observed over a single neapspring cycle is responsible for the accordingly large variability in wave skewness, asymmetry and breaking processes, and thus in sediment fluxes and morphological changes.
ICS 2016 Sydney
Sydney, Australia

hal-01254465
https://hal.archives-ouvertes.fr/hal-01254465
DOI : 10.2112/SI75-075.1

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
Absolute Mα x-ray production cross sections have been measured and calculated for heavy elements Au, Pb, Bi, and U for electron incident energies from the ionization threshold up to 38 keV. The experimental cross sections were deduced from M x-ray intensities emitted from ultrathin samples of the elements of interest deposited onto self-supporting C films. The measurements were performed using two electron microprobes and several wavelength-dispersive spectrometers. X-ray intensities were converted into x-ray production cross sections by using estimated values of the number of incident electrons, target thickness, and spectrometer efficiency. Experimental results are compared with calculated cross sections using different predictive formulae. Good agreement is found between the measured cross sections and the predictions from the distorted-wave Born approximation, which indicates that this approximation is suited for the calculation of M-shell ionization cross sections of heavy elements.
ISSN: 0142-2421

hal-01122839
https://hal.archives-ouvertes.fr/hal-01122839
DOI : 10.1002/sia.5561

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
Absolute M-shell x-ray production cross sections have been measured and calculated for Au and Bi for electron incident energies from close to the ionization threshold up to 38 keV. The experimental cross sections were deduced from M alpha x-ray intensities emitted from ultrathin Au and Bi samples deposited on self-supporting C films. The measurements were performed on an electron microprobe using several wavelength-dispersive spectrometers. The x-ray production cross sections were also evaluated theoretically using ionization cross sections calculated from the plane-wave and the distorted-wave Born approximations. Experimental results are compared with the calculated cross sections and also with the results of two analytical formulas widely used in many applications. Good agreement is found between the measured cross sections and the predictions from the distorted-wave Born approximation, which indicates that this approximation is suited for the calculation of M-shell ionization cross sections of heavy elements.
ISSN: 1050-2947

hal-00411432
https://hal.archives-ouvertes.fr/hal-00411432
DOI : 10.1103/PhysRevA.78.022704

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Progress in seismic methodology and ambitious large-scale seismic projects are enabling high-resolution imaging of the continental crust. The ability to constrain interpretations of crustal seismic data is based on laboratory measurements on rock samples and calculations of seismic properties. Seismic velocity calculations and their directional dependence are based on the rock microfabric, which consists of mineral aggregate properties including crystallographic preferred orientation (CPO), grain shape and distribution, grain boundary distribution, and misorientation within grains. Single-mineral elastic constants and density are crucial for predicting seismic velocities, preferably at conditions that span the crust. However, high-temperature and high-pressure elastic constant data are not as common as those determined at standard temperature and pressure (STP; atmospheric conditions). Continental crust has a very diverse mineral composition; however, a select number of minerals appear to dominate seismic properties because of their high-volume fraction contribution. Calculations of microfabric-based seismic properties and anisotropy are performed with averaging methods that in their simplest form takes into account the CPO and modal mineral composition, and corresponding single crystal elastic constants. More complex methods can take into account other microstructural characteristics, including the grain shape and distribution of mineral grains and cracks and pores. Dynamic or active wave propagation schemes have recently been developed, which offer a complementary method to existing static averaging methods generally based on the use of the Christoffel equation. A challenge for the geophysics and rock physics communities is the separation of intrinsic factors affecting seismic anisotropy, due to properties of crystals within a rock and apparent sources due to extrinsic factors like cracks, fractures, and alteration. This is of particular importance when trying to deduce crustal composition and the state of deformation from seismic parameters.
ISSN: 8755-1209

Droits : info:eu-repo/semantics/OpenAccess
hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568
https://hal.archives-ouvertes.fr/hal-01685568/document
https://hal.archives-ouvertes.fr/hal-01685568/file/Almqvist_et_al-2017-Reviewssur Geophysics.pdf
DOI : 10.1002/2016RG000552

Éditeur(s) : HAL CCSD
Résumé : International audience
The present research work is a part of the KUNSHEN Franco-Taiwanese research project which aims at investigating the hydro/morphodynamics of barrier islands driven by typhoon events. This study focuses on the impact of the Talim tropical storm on the Wan-tzu-liao sand barrier (Taiwan) in terms of water level rising and watertable overheight. In-situ measurements are provided by a cross-shore network of pressure sensors extended from the intertidal zone to the top of the barrier. Extreme offshore wave conditions are encountered during Talim, with significant wave height greater than 10m at the storm peak. It is shown that measured setups are smaller than those predicted by usual empirical parameterization. Groundwater dynamics is strongly affected by the storm, with watertable overheight of the order of one meter under the barrier top. Watertable dynamics is influenced by waves, tides and rainfalls.
Coastal Dynamics 2013

hal-00831573
https://hal.archives-ouvertes.fr/hal-00831573

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We have analyzed shear wave splitting recorded by portable and permanent broadband and long-period stations located in the eastern United States. Teleseismic shear waves (SKS, SKKS, and PKS) were used to retrieve the splitting parameters: the orientation of the fast wave polarization plane ϕ and the delay time δt. In total, 120 seismic events were processed, allowing for more than 600 splitting measurements. Within the Appalachians, stations located in the western (external) part are characterized by δt≈1s and ϕ trending N50°– 70°E in the south and central regions and N30°–40°E in the north, closely following the trend of the orogenic belt in these areas. The transition region between north and central is characterized by δt≈1–1.3 s and by E-W trending ϕ that are at a high angle to the regional geologic trend. Measurements at two stations located in the eastern (internal) part of the belt indicate very weak anisotropy. The large-scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate. Splitting along the southern and eastern margins of the continent is consistent with that expected for Grenvillian deformation, an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out. Within the cratonic core, the correlation between δt and lithospheric thickness suggests a lithospheric anisotropy. Smaller-length-scale variations also argue for a significant contribution of lithospheric structures. The fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern United States, i.e., the Grenville and Appalachian orogenies and the subsequent rifting of the North Atlantic Ocean. Our observations in the western Appalachians suggest that the anisotropy may be preserved since the Grenvillian orogeny. The absence of detectable splitting in the two stations in the eastern Appalachians is attributed to the igneous intrusions related to the Atlantic rifting. The measurements in the transition between the northern and central southern Appalachians, constitute an intriguing anomaly, whose E-W ϕ have little obvious relation to the regional surface geology. We suggest two possible causes: (1) the local dominance of asthenospheric flow, motivated by the proximity of a pervasive low-velocity anomaly and (2) lithospheric deformation in a transcontinental strike-slip fault zone active during the Appalachian collision.
ISSN: 2169-9313

hal-01388859
http://hal.univ-reunion.fr/hal-01388859
http://hal.univ-reunion.fr/hal-01388859/document
http://hal.univ-reunion.fr/hal-01388859/file/Barruol_JGR_1997.pdf
DOI : 10.1029/96JB03800

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes.
ISSN: 0956-540X

hal-01388809
http://hal.univ-reunion.fr/hal-01388809
http://hal.univ-reunion.fr/hal-01388809/document
http://hal.univ-reunion.fr/hal-01388809/file/Barruol_swell_GJI2006.pdf
DOI : 10.1111/j.1365-246X.2006.02871.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Ocean loading effects cause 3-D displacements large enough to affect space geodesy measurements either at the subdiurnal periods or at longer time scales by the means of spurious signals. GPS measurements, in turn, could provide local improvements of the models in coastal areas if their ability to precisely monitor such rapid displacements is assessed. In this paper, we use 105 days of continuous GPS measurements collected in 2004 in the French Brittany and Cotentin region to investigate: (1) the precision achieved by the GPS analysis on measuring 3-D subdiurnal displacements and amplitude and phase of the tidal constituents, (2) the quality of the most recent ocean tide model FES2004 in such a complex coastal context. Indeed, in this area, tide amplitudes are among the largest in the world (up to 16 cm of loading displacements on the vertical component) and are believed to show strong shallow-water tides. From a state of the art GPS analysis using the scientific GAMIT software over 2-h sessions, we test two independent strategies for the realization of the reference frame. The position time series are then compared with the displacements predicted by the FES2004 model applied on an elastic Earth model. The two sets of results are consistent with each other at the same level of agreement than with the predicted displacements, namely 3–5 mm on the horizontal components, 10 mm on the vertical. This assesses the capability of this technique for measuring 3-D ocean tide loading deformation. We validate the FES2004 model in the Brittany area, even though it slightly (2–7 mm) underestimates the three components amplitudes. With a harmonic analysis of the observed position time series, we obtain nevertheless an agreement at a submillimetre level for the M2, N2, O1, Q1 tidal constituents and at a millimetre level for the K1 and S2 tidal constituents. Moreover, we can extract a significant M4 load signal at the 95 per cent confidence level from the GPS time series at the stations located in the Mont St Michel area. The detection of other shallow-water constituents would be helpful to understand the amplitude deficit between the FES2004 predicted and GPS observed displacements.
ISSN: 0956-540X

insu-00335909
https://hal-insu.archives-ouvertes.fr/insu-00335909
https://hal-insu.archives-ouvertes.fr/insu-00335909/document
https://hal-insu.archives-ouvertes.fr/insu-00335909/file/Vergnolle_GJI_08_revised.pdf
DOI : 10.1111/j.1365-246X.2008.03734.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes.
ISSN: 0956-540X

hal-01323691
http://hal.univ-reunion.fr/hal-01323691
http://hal.univ-reunion.fr/hal-01323691/document
http://hal.univ-reunion.fr/hal-01323691/file/Barruol_et_al_2006.pdf
DOI : 10.1111/j.1365-246X.2006.02871.x

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Chromatin modification enzymes are important regulators of gene expression and some are evolutionarily conserved from yeast to human. Saccharomyces cerevisiae is a major model organism for genome-wide studies that aim at the identification of target genes under the control of conserved epigenetic regulators. Ume6 interacts with the upstream repressor site 1 (URS1) and represses transcription by recruiting both the conserved histone deacetylase Rpd3 (through the co-repressor Sin3) and the chromatin-remodeling factor Isw2. Cells lacking Ume6 are defective in growth, stress response, and meiotic development. RNA profiling studies and in vivo protein-DNA binding assays identified mRNAs or transcript isoforms that are directly repressed by Ume6 in mitosis. However, a comprehensive understanding of the transcriptional alterations, which underlie the complex ume6Δ mutant phenotype during fermentation, respiration, or sporulation, is lacking. We report the protein-coding transcriptome of a diploid MAT a/α wild-type and ume6/ume6 mutant strains cultured in rich media with glucose or acetate as a carbon source, or sporulation-inducing medium. We distinguished direct from indirect effects on mRNA levels by combining GeneChip data with URS1 motif predictions and published high-throughput in vivo Ume6-DNA binding data. To gain insight into the molecular interactions between successive waves of Ume6-dependent meiotic genes, we integrated expression data with information on protein networks. Our work identifies novel Ume6 repressed genes during growth and development and reveals a strong effect of the carbon source on the derepression pattern of transcripts in growing and developmentally arrested ume6/ume6 mutant cells. Since yeast is a useful model organism for chromatin-mediated effects on gene expression, our results provide a rich source for further genetic and molecular biological work on the regulation of cell growth and cell differentiation in eukaryotes.
ISSN: 1617-4615

hal-01151619
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01151619
DOI : 10.1007/s00438-015-1051-5
PUBMED : 25957495

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : We provide evidence for a plume-like upwelling beneath the Eifel hotspot, Western Germany, by using teleseismic shear-wave splitting to resolve the anisotropy associated with upwelling flow that is spreading laterally into the asthenosphere. The variation in fast-polarization azimuth we find across the Eifel hotspot is explained by a model of slowly upwelling material that is horizontally being deflected or sheared in a parabolic asthenospheric flow (PAF) pattern toward west-southwest, a direction that correlates with Eurasian absolute plate motion. We suggest that the lack of an age progression for Eifel volcanism, which is expected for a fixed-upwelling model, is a result of (1) sporadic volcanism due to a low excess plume temperature and/or varying crustal stresses that periodically relax and facilitate eruption, and (2) complex upwelling flow pathways and/or Late Tertiary changes in the slow Eurasian plate motion. The success of the PAF model in fitting the data is remarkable given the small number of parameters (four) and the consistency with the plate motion direction determined from geology and/or geodesy. This suggests that a predictable mantle-anisotropy pattern may exist also for other hotspots driven by plume-like upwellings, and that splitting can be a useful diagnostic to differentiate between plume-like and alternative sources for mantle hotspots.
Mantle plumes - a multidisciplinary approach

hal-00407986
https://hal.archives-ouvertes.fr/hal-00407986
DOI : 10.1007/978-3-540-68046-8