Slab segmentation controls the interplate slip motion in the SW Hellenic subduction: New insight from the 2008Mw 6.8 Methoni interplate earthquake

We present an integrated approach of the seismic structure and activity along the offshore SW Hellenic subduction from combined observations of marine and land seismic stations. Our imaging of the slab top topography from teleseismic receiver function analysis at ocean bottom seismometers supports a trenchward continuation of the along-dip slab faults beneath the Peloponnesus. We further show that their morphostructural control accounts for the backstepping of the thrust contact of the Mediterranean Ridge accretionary wedge over the upper plate. Local seismic activity offshore SW Peloponnesus constrained by ocean bottom seismometer observations reveals a correlation with specific features of the forearc: the Matapan Troughs. We study the Mw6.8 14.02.2008 interplate earthquake offshore SW Peloponnesus and show that its nucleation, rupture zone, and aftershocks sequence are confined to one slab panel between two adjacent along-dip faults and are thus controlled by not only the offshore slab top segmentation but also the upper plate sea-bottom morphology

Synthesis of novel MMT/acyl-protected nucleo alanine monomers for the preparation of DNA/alanyl-PNA chimeras

Alanyl-peptide nucleic acid (alanyl-PNA)/DNA chimeras are oligomers envisaged to be beneficial in efficient DNA diagnostics based on an improved molecular beacon concept. A synthesis of alanyl-PNA/DNA chimera can be based on the solid phase assembly of the oligomer with mixed oligonucleotide/peptide backbone under DNA synthesis conditions, in which the nucleotides are introduced as phosphoramidites, whereas the nucleo amino acids make use of the acid labile monomethoxytrityl (MMT) group for temporary protection of the α-amino groups and acyl protecting groups for the exocyclic amino functions of the nucleobases. In this work, we realized for the first time the synthesis of all four MMT/acyl-protected nucleo alanines, achieved by deprotection/reprotection of the newly synthesized Boc/acyl intermediates, useful monomers for the obtainment of (alanyl-PNA)/DNA chimeras by conditions fully compatible with the standard phosphoramidite DNA synthesis strategy

Classifying airborne radiometry data with Agglomerative Hierarchical Clustering: A tool for geological mapping in context of rainforest (French Guiana)

International audienceIn highly weathered environments, it is crucial that geological maps provide information concerning both the regolith and the bedrock, for societal needs, such as land-use, mineral or water resources management. Often, geologists are facing the challenge of upgrading existing maps, as relevant information concerning weathering processes and pedogenesis is currently missing. In rugged areas in particular, where access to the field is difficult, ground observations are sparsely available, and need therefore to be complemented using methods based on remotely sensed data.For this purpose, we discuss the use of Agglomerative Hierarchical Clustering (AHC) on eU, K and eTh airborne gamma-ray spectrometry grids. The AHC process allows primarily to segment the geophysical maps into zones having coherent U, K and Th contents. The analysis of these contents are discussed in terms of geochemical signature for lithological attribution of classes, as well as the use of a dendrogram, which gives indications on the hierarchical relations between classes.Unsupervised classification maps resulting from AHC can be considered as spatial models of the distribution of the radioelement content in surface and sub-surface formations. The source of gamma rays emanating from the ground is primarily related to the geochemistry of the bedrock and secondarily to modifications of the radioelement distribution by weathering and other secondary mechanisms, such as mobilisation by wind or water. The interpretation of the obtained predictive classified maps, their U, K, Th contents, and the dendrogram, in light of available geological knowledge, allows to separate signatures related to regolith and solid geology. Consequently, classification maps can be integrated within a GIS environment and used by the geologist as a support for mapping bedrock lithologies and their alteration.We illustrate the AHC classification method in the region of Cayenne using high-resolution airborne radiometric data acquired in 1996 across most of French Guiana. Access to the field in this region, almost entirely covered by tropical rainforest, is difficult, and therefore, use of airborne geophysical data is highly suitable to complement ground observations. Despite the vegetal cover, the U, K and Th maps, exhibit to the first order, a fairly good correlation with lithological units recognised by geologists in the field.Consequently, classification of the radiometric data is globally concordant with existing 1:100,000-scale geological map. In addition, using the radioelement contents and relations between classes at different levels of classification, additional relevant information concerning weathering effects, unexpected lithological differences or transfer by erosion, are evidenced

Transcranial stimulation excites virtually all motor neurons supplying the target muscle. A demonstration and a method improving the study of motor evoked potentials

Transcranial stimulation has become an established method in the evaluation of corticospinal tract function. Clinical studies mainly address slowing of conduction through measurement of increased central conduction time (CCT) and 'failures' of conduction through observation of marked reductions in the size of the motor evoked potential (MEP). While CCT is of great interest in detecting subclinical slowing of conduction, the method discloses only gross failures of conduction, since the size of the MEP varies markedly between normal subjects and from one stimulus to another, leading to a broad range of normal values. Furthermore, transcranial stimulation does not appear to achieve depolarization of all spinal motor neurons leading to the target muscles, since in most normal subjects MEPs are smaller in amplitude than the responses evoked by peripheral nerve stimulation. We have developed a triple stimulation technique (TST) which, through two collisions, links central to peripheral conduction and suppresses desynchronization of MEPs. This technique shows that transcranial stimulation does achieve depolarization of all, or nearly all, spinal motor neurons supplying the target muscle in healthy subjects. Our data thus demonstrate that the amplitudes of MEPs are (i) smaller than those of peripheral responses, mostly due to phase cancellation of the action potentials caused by the desynchronization occurring within the corticospinal tract or at spinal cell level and (ii) variable between normal subjects and from one stimulus to another, mostly due to variability of this desynchronization. This technique provides new insights into normal corticospinal tract conduction. It will improve detection and quantification of central motor conduction failure

Semi-automated structural analysis of high resolution magnetic and gamma-ray spectrometry airborne surveys

International audienceA user-controlled procedure was implemented for the structural analysis of geophysical maps. Local edge segments are first extracted using a suitable edge detector function, then linked into straight discontinuities and, finally, organised in complex boundary lines best delineating geophysical features. Final boundary lines may be attributed by a geologist to lithological contacts and/or structural geological features.Tests of some edge detectors, (i) horizontal gradient magnitude (HGM), (ii) various orders of the analytic signal (An), reduced to the pole or not, (iii) enhanced horizontal derivative (EHD), (iv) composite analytic signal (CAS), were performed on synthetic magnetic data (with and without noise). As a result of these comparisons, the horizontal gradient appears to remain the best operator for the analysis of magnetic data. Computation of gradients in the frequency domain, including filtering and upward continuation of noisy data, is well-suited to the extraction of magnetic gradients associated to deep sources, while space-domain smoothing and differentiation techniques is generally preferable in the case of shallow magnetic sources, or for gamma-ray spectrometry analysis.Algorithms for edge extraction, segment linking, and line following can be controlled by choosing adequate edge detector and processing parameters which allows adaptation to a desired scale of interpretation. Tests on synthetic and real case data demonstrate the adaptability of the procedure and its ability to produce basic layer for multi-data analysis. The method was applied to the interpretation of high-resolution airborne magnetic and gamma-ray spectrometry data collected in northern Namibia. It allowed the delineation of dyke networks concealed by superficial weathering and demonstrated the presence of lithological variations in alluvial flows. The output from the structural analysis procedure are compatible with standard GIS softwares and enable the geologist to (i) compare the structural features with various data sets in a common geo-referenced frame, and (ii) take advantage of attribute selection to highlight specific structural patterns or eliminate possible artefacts