Structural and Geochronological Study of High‐Pressure Metamorphic Rocks in the Kekesu Section (Northwestern China): Implications for the Late Paleozoic Tectonics of the Southern Tianshan

International audienceBlueschist- and eclogite-facies high- to ultrahigh-pressure (HP/UHP) metamorphic rocks occur in the southern Tianshan Belt. Their deformation and metamorphic history is important for understanding the Paleozoic tectonics of the Central Asian Orogenic Belt. Our study focuses on the structural analysis and geochronology of the HP metamorphic rocks and the surrounding rocks in the Kekesu Section in the southern Chinese Tianshan. Geometric and kinematic analyses indicate three ductile deformation events: a top-to-the-north thrusting, a top-to-the-south shearing, and a dextral wrenching. New 40Ar/39Ar laser probe plateau ages were obtained on white mica from retrograde blueschist ( 316+/-2and331+/-1Ma; 1j) and greenschist-facies metasediments (323+/-1 Ma; 1j). These ages are interpreted as the time of retrograde recrystallization during exhumation of the HP metamorphic rocks. New structural and isotopic data, in conjunction with previous results, suggest that (1) the collision event occurred during the latest Devonian to earliest Carboniferous, resulting in HP/UHP metamorphism and the top-to-the-north thrusting; (2) the postcollisional exhumation of the HP/UHP metamorphic rocks and extensive retrograde metamorphism under greenschistfacies conditions took place in the Mid-Late Carboniferous and are correlated with south-dipping normal faulting; and (3) Permian ductile dextral shearing and associated granitic intrusion and fluid activity severely overprinted the earlier fabrics

Water in Comets 71P/Clark and C/2004 B1 (LINEAR) with Spitzer

We present 5.5 to 7.6 micron spectra of comets 71P/Clark (2006 May 27.56 UT,r_h = 1.57 AU pre-perihelion) and C/2004 B1 (LINEAR) (2005 October 15.22 UT,r_h = 2.21 AU pre-perihelion and 2006 May 16.22 UT, r_h = 2.06 AUpost-perihelion) obtained with the Spitzer Space Telescope. The nu_2vibrational band of water is detected with a signal-to-noise ratio of 11 to 50.Fitting the spectra using a fluorescence model of water emission yields a waterrotational temperature of < 18 K for 71P/Clark and approximately less than orequivalent to 14 +/- 2 K (pre-perihelion) and 23 +/- 4 K (post-perihelion) forC/2004 B1 (LINEAR). The water ortho-to-para ratio in C/2004 B1 (LINEAR) ismeasured to be 2.31 +/- 0.18, which corresponds to a spin temperature of26^{+3}_{-2} K. Water production rates are derived. The agreement between thewater model and the measurements is good, as previously found for Spitzerspectra of C/2003 K4 (LINEAR). The Spitzer spectra of these three comets do notshow any evidence for emission from PAHs and carbonate minerals, in contrast toresults reported for comets 9P/Tempel~1 and C/1995 O1 (Hale-Bopp).

Filtering for distributed mechanical systems using position measurements: perspectives in medical imaging

International audienceWe propose an effective filtering methodology designed to perform estimation in a distributed mechanical system using position measurements. As in a previously introduced method, the filter is inspired from robust control feedback, but here we take full advantage of the estimation specificity to choose a feedback law that can act on displacements instead of velocities and still retain the same kind of dissipativity property which guarantees robustness. This is very valuable in many applications for which positions are more readily available than velocities, as in medical imaging. We provide an in-depth analysis of the proposed procedure, as well as detailed numerical assessments using a test problem inspired from cardiac biomechanics, as medical diagnosis assistance is an important perspective for this approach. The method is formulated first for measurements based on Lagrangian displacements, but we then derive a nonlinear extension allowing to instead consider segmented images, which of course is even more relevant in medical applications

Human exposure to high natural background radiation: what can it teach us about radiation risks?

Natural radiation is the major source of human exposure to ionising radiation, and its largest contributing component to effective dose arises from inhalation of (222)Rn and its radioactive progeny. However, despite extensive knowledge of radiation risks gained through epidemiologic investigations and mechanistic considerations, the health effects of chronic low-level radiation exposure are still poorly understood. The present paper reviews the possible contribution of studies of populations living in high natural background radiation (HNBR) areas (Guarapari, Brazil; Kerala, India; Ramsar, Iran; Yangjiang, China), including radon-prone areas, to low dose risk estimation. Much of the direct information about risk related to HNBR comes from case-control studies of radon and lung cancer, which provide convincing evidence of an association between long-term protracted radiation exposures in the general population and disease incidence. The success of these studies is mainly due to the careful organ dose reconstruction (with relatively high doses to the lung), and to the fact that large-scale collaborative studies have been conducted to maximise the statistical power and to ensure the systematic collection of information on potential confounding factors. In contrast, studies in other (non-radon) HNBR areas have provided little information, relying mainly on ecological designs and very rough effective dose categorisations. Recent steps taken in China and India to establish cohorts for follow-up and to conduct nested case-control studies may provide useful information about risks in the future, provided that careful organ dose reconstruction is possible and information is collected on potential confounding factors.

Environment of titanium and aluminum in a magnesium alumino-silicate glass

International audienceThe structure of the glass 2MgO–2Al2 O3 –5SiO2 –TiO2 was investigated using neutron diffraction with isotopic substitution. Reverse Monte Carlo (RMC) modeling was used to reproduce experimental structure factors derived from diffraction experiments. The local environment of titanium atoms was determined and it corresponds to an average of 5.4 ± 0.2 oxygen atoms at a mean distance of 1.86 ± 0.02 ̊A. This coordination number agrees with the predominance of fivefold coordination, with the coexistence of four- and sixfold coordination in similar amounts. 27 Al nuclear magnetic resonance (NMR) results revealed that the proportion of highly coordinated aluminum atoms in this titanium-bearing glass was higher than in the titanium-free sample. RMC modeling was used to interpret the structural role of these [5] Al species and we show a trend for preferential bonding between [5] Al and Ti atoms. This favored linkage is important to understand the role of titanium dioxide as a nucleating agent in inorganic glass-ceramics fabrication

Flexible relaxor materials: Ba2PrxNd1−xFeNb4O15tetragonal tungsten bronze solid solution

International audienceRelaxors are very interesting materials but most of the time they are restricted to perovskite materials and thus their flexibility is limited. We have previously shown that tetragonal tungsten bronze (TTB) niobate Ba2PrFeNb4O15 was a relaxor below 170 K and that Ba2NdFeNb4O15 displays a ferroelectric behavior with a TC = 323 K. On scanning the whole solid solution Ba2PrxNd1−xFeNb4O15 (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1), we demonstrate here a continuous crossover between these end member behaviors with a coexistence of ferroelectricity and relaxor in the intermediate range. This tunability is ascribed to the peculiar structure of the TTB networks which is more open than the classical perovskites. This allows for the coexistence of long range and short range orders and thus opens up the range of relaxor materials

Focus on the neural interface

Focus on the neural interface

Nanosafe 2008: International Conference on Safe production and use of nanomaterials

Welcome from the organizers The rapidly developing field of nanotechnology opens up many exciting opportunities and benefits for new materials with significantly improved properties as well as some revolutionary applications in the fields of energy, environment, medicine, etc. These new materials potentially pave the way to considerable innovations in many industries of the 21st century although associated risks must be perfectly under control for workers, consumers and the environment. So, one can easily understand why Nanosafety is now considered as a specific new scientific area, gaining in importance and maturity every day. Following the successful outcome of the two past international conferences on the safe production and use of nanomaterials: Nanosafe 2008 and 2010, the organizing committee has the pleasure of welcoming again to Grenoble some of the most famous specialists of the field in the world. In addition to the standard issues addressed in previous nanosafe conferences such as Toxicology, Eco-toxicology, Expology, Detection, Life Cycle Analysis, Regulation and Standardization, new topics of great interest will be dealt with this year, concerning Governance and practical Risk Management for OSH experts and Societal issues. In order to enhance the exchanges and conviviality three debates werw organized around Nano Governance, Toxicology and Ethics. We hope that you will appreciate this new Nanosafe edition like the previous ones. This is your Nanosafe conference, please enjoy. The Nanosafe conference organisers Francois Tardif and Frederic Shuster Management Vanessa Gaultier Francois TardifFrederic Shuster Vanessa Gaultier Local Organizing Committee Vanessa GAULTIER (CEA) Francois TARDIF (CEA) Dominique BAGUET (CEA) Frededric SHUSTER (CEA) Yves SICARD (CEA) Catherine DURAND (CEA) Didier MOLKO (MINATEC) International Scientific Committee Chair: Frederic SCHUSTER (CEA, FR) Francois TARDIF (CEA, FR) Co-chair: Georgios KATALAGARIANAKIS (EC, BE) Melanie AUFFAN (CEREGE, FR) Jorge BOCZKOWSKI (INSERM, FR) Jean-Yves BOTTERO (CEREGE, FR) Jacques BOUILLARD (INERIS, FR) Derk BROUWER (TNO, NL) Marie CARRIERE (CEA, FR) Claude EMOND (U. MONTREAL, CA) Cassandra ENGEMAN (UCSB, USA) Eric GAFFET (CNRS, FR) Francois GENSDARMES (IRSN, FR) Alexei GRINBAUM (CEA, FR) Antje GROBE (U.STUTTGART, DE) Peter HOET (KUL, BE) Eric QUEMENEUR (CEA, FR) Olivier LE BIHAN (INERIS, FR) Robert MUIR (NANEUM, UK) Tinh NGUYEN (NIST, USA) Bernd NOWACK (EMPA, CH) Gunter OBERDORSTER (U. ROCHESTER, USA) David PUI (U. MINNESOTA, USA) Michael RIEDIKER (IST, CH) Yves SAMSON (CEA, FR) Ken TAKEDA (U. TOKYO, JP) Olivier WITSCHGER (INRS, FR) The PDF contains a list of sponsor logos, the conference programme and planning documents.

Experimental study of the response functions of direct-reading instruments measuring surface-area concentration of airborne nanostructured particles

An increasing number of experimental and theoretical studies focus on airborne nanoparticles (NP) in relation with many aspects of risk assessment to move forward our understanding of the hazards, the actual exposures in the workplace, and the limits of engineering controls and personal protective equipment with regard to NP. As a consequence, generating airborne NP with controlled properties constitutes an important challenge. In parallel, toxicological studies have been carried out, and most of them support the concept that surface-area could be a relevant metric for characterizing exposure to airborne NP [1]. To provide NP surface-area concentration measurements, some direct-reading instruments have been designed, based on attachment rate of unipolar ions to NP by diffusion. However, very few information is available concerning the performances of these instruments and the parameters that could affect their responses. In this context, our work aims at characterizing the actual available instruments providing airborne NP surface-area concentration. The instruments (a- LQ1-DC, Matter Engineering; b-AeroTrak™ 9000, TSI; c- NSAM, TSI model 3550;) are thought to be relevant for further workplace exposure characterization and monitoring. To achieve our work, an experimental facility (named CAIMAN) was specially designed, built and characterized.