Changes In The Permeability, Streaming Potential And Resistivity Of A Claystone From The Nankai Prism Under Stress.

International audienc

First laboratory measurements of seismo-magnetic conversions in fluid-filled Fontainebleau sand

International audienceSeismic wave propagation in fluid-filled porous materials induces electromagnetic effects due to small relative pore-fluid motions. In order to detect the seismo-magnetic couplings theoretically predicted by Pride (1994), we have designed a small-scale experiment in a low-noise underground laboratory which presents exceptional electromagnetic shielding conditions. Our experiment included accelerometers, electric dipoles and induction magnetometers to characterize the seismo-electromagnetic propagation phenomena. To assess the electrokinetic origin of the measured electric and magneticfields, we compared records obtained in dry and fluid-filled sand. Extra care has been taken to ensure the mechanical decoupling between the sand column and the magnetometers to avoid spurious vibrations of the magnetometers and misinterpretations of the recorded signals. Our results show that seismo-electric and seismo-magnetic signals are associated with different wave propagation modes, thus emphasizing the electrokinetic origin of these effects

Evidence of the theoretically predicted seismo-magnetic conversion

We acknowledge the Geophysical Journal International and the Association/Society and Blackwell Publishing. The definitive version is available at www.wileyinterscience.com. The reference is : Bordes, C., L. Jouniaux, S. Garambois, M. Dietrich, J.-P. Pozzi, and S. Gaffet, Evidence of the theoretically predicted seismo-magnetic conversion, G.J.I., 174, issue 2, 489-504, doi:10.1111/j.1365-246X.2008.03828.xInternational audienceSeismo-electromagnetic phenomena in porous media arise from seismic wave-induced fluid motion in the pore space, which perturbs the equilibrium of the electric double layer. This paper describes with details the original experimental apparatus built within the ultra-shielded chamber of the Low Noise Underground Laboratory of Rustrel (France). We measured seismo-magnetic conversions in moist sand using two induction magnetometers, and a pneumatic seismic source to generate the seismic wave propagation. We ensured to avoid the magnetometer vibrations, which could induce strong disturbances from induction origin. Interpretation of the data is improved by an analytical description of phase velocities for fast (P_f) and slow (P_s) longitudinal modes, transverse mode (S) as well as the extensional mode due to the cylindrical geometry of the sample. The purpose of this paper is to provide elements to measure correctly co seismic seismomagnetic fields and to specify their amplitude. The seismic arrivals recorded in the sample showing a 1200$-1300 m/s velocity have been associated to P and extensional waves. The measured seismo-magnetic arrivals show a velocity of about 800 m/s consistent with the calculated phase velocity of S waves. Therefore we show that the seismo-magnetic field is associated to the transverse part of the propagation, as theoretically predicted by Pride (1994), but never measured up to now. Moreover, the combined experimental and analytical approaches lead us to the conclusion that the measured seismo-magnetic field is probably about 0.35 nT for a 1 m/s2 seismic source acceleration (0.1 g)

Premiers résultats d'une étude pluridisciplinaire sur des travertins quaternaires du Maroc

Suite aux résultats de l’étude préliminaire réalisée sur l’affleurement de travertin d’Irdi (Errachidia) (Boudad et al., 2003), un carottage a été fait en novembre 2005 sur ce site afin de déterminer l’épaisseur des formations travertineuses. L’étude a été ensuite étendue à d’autres affleurements travertineux marocains en ayant recours à des méthodes d’analyse complémentaires (palynologie, paléomagnétisme) pour identifier les différentes phases de concrétionnement et pour mieux cerner le cadre paléoclimatique de ces formations. Des encroûtements travertineux actuels qui se forment aujourd’hui à Irdi dans l’oued Ziz ont été analysés afin demieux appréhender les processus physico-chimiques qui président à la cristallisation de ces structures ; en particulier, la mesure du rapport d’activité 234U/238U montre que l’eau responsable de la formation des travertins fossiles avait la même origine que celle d’aujourd’hui. Plusieurs phases de concrétionnement, qui se répartissent du Pléistocène supérieur au Pléistocène moyen, ont été identifiées. Ces phases devront être intégrées dans l’évolution climatique du Maroc et corrélées aux stades glaciaires et interglaciaires déterminés en milieu marin.After a preliminary study of the travertine outcrop of Irdi (Errachidia province), this site was drilled and the survey was extended to other exposures in Morocco. Complementary methods of investigation were used (palynology, paleomagnetism) together with U-series analyses in order to identify the successive deposition phases and to precise the associated paleoclimatic framework. For a better understanding of the travertine formation, we have studied the travertine formations which are presently forming at Irdi. The respective 234U/238U activity ratios of the present water and fossil travertines are similar, i.e. physical and chemical conditions of travertinization were more or less similar today as in the past. Several crystallization phases were identified from Upper Pleistocene to Middle Pleistocene. These phases must be integrated into the climatic evolution of Morocco and correlated to glacial and interglacial stages defined in marine environment

Role of the Single-Stranded DNA–Binding Protein SsbB in Pneumococcal Transformation: Maintenance of a Reservoir for Genetic Plasticity

Bacteria encode a single-stranded DNA (ssDNA) binding protein (SSB) crucial for genome maintenance. In Bacillus subtilis and Streptococcus pneumoniae, an alternative SSB, SsbB, is expressed uniquely during competence for genetic transformation, but its precise role has been disappointingly obscure. Here, we report our investigations involving comparison of a null mutant (ssbB−) and a C-ter truncation (ssbBΔ7) of SsbB of S. pneumoniae, the latter constructed because SSBs' acidic tail has emerged as a key site for interactions with partner proteins. We provide evidence that SsbB directly protects internalized ssDNA. We show that SsbB is highly abundant, potentially allowing the binding of ∼1.15 Mb ssDNA (half a genome equivalent); that it participates in the processing of ssDNA into recombinants; and that, at high DNA concentration, it is of crucial importance for chromosomal transformation whilst antagonizing plasmid transformation. While the latter observation explains a long-standing observation that plasmid transformation is very inefficient in S. pneumoniae (compared to chromosomal transformation), the former supports our previous suggestion that SsbB creates a reservoir of ssDNA, allowing successive recombination cycles. SsbBΔ7 fulfils the reservoir function, suggesting that SsbB C-ter is not necessary for processing protein(s) to access stored ssDNA. We propose that the evolutionary raison d'être of SsbB and its abundance is maintenance of this reservoir, which contributes to the genetic plasticity of S. pneumoniae by increasing the likelihood of multiple transformation events in the same cell

ECMO for COVID-19 patients in Europe and Israel

Since March 15th, 2020, 177 centres from Europe and Israel have joined the study, routinely reporting on the ECMO support they provide to COVID-19 patients. The mean annual number of cases treated with ECMO in the participating centres before the pandemic (2019) was 55. The number of COVID-19 patients has increased rapidly each week reaching 1531 treated patients as of September 14th. The greatest number of cases has been reported from France (n = 385), UK (n = 193), Germany (n = 176), Spain (n = 166), and Italy (n = 136) .The mean age of treated patients was 52.6 years (range 16–80), 79% were male. The ECMO configuration used was VV in 91% of cases, VA in 5% and other in 4%. The mean PaO2 before ECMO implantation was 65 mmHg. The mean duration of ECMO support thus far has been 18 days and the mean ICU length of stay of these patients was 33 days. As of the 14th September, overall 841 patients have been weaned from ECMO support, 601 died during ECMO support, 71 died after withdrawal of ECMO, 79 are still receiving ECMO support and for 10 patients status n.a. . Our preliminary data suggest that patients placed on ECMO with severe refractory respiratory or cardiac failure secondary to COVID-19 have a reasonable (55%) chance of survival. Further extensive data analysis is expected to provide invaluable information on the demographics, severity of illness, indications and different ECMO management strategies in these patients