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Acute exposure to oil and oil dispersants can cause a wide range of physiological dysfunctions in marine fish species and evidences for consequences on behaviour are also increasing. In response to the presence of predators or to food availability, the modulation of locomotor activity and schools' behaviour enable fish to maximize their survival rates. However, the degree to which this regulatory process is affected by exposure to oil and/or dispersants is yet unknown. Here we investigated the effect of a 62-h experimental exposure to dispersant-treated oil on the behavioural (shoal cohesion, spontaneous activity) and metabolic (oxygen consumption) responses to simulated predation in juvenile European sea bass, Dicentrarchus labrax L. Our results suggest that exposure to petroleum hydrocarbons may affect negatively individual fitness through impaired ability to respond to predation. Shoal cohesion was not affected, but fish swimming activity was higher than control individuals under predation pressure and the amplitude of their metabolic response was significantly reduced. Fish recovered from alteration of their metabolic response 7 days post-exposure. Additionally, a strong habituation component was observed in C fish and the absence of such pattern in E fish suggest altered capacity to habituate over time to the surrounding environment and possible impairments of the related cognitive performances. Altogether, our data show that juvenile sea bass exposed to oil exhibit transient physiological dysfunctions and impairments of complex behaviours that may have major population-level consequences.

International audience; Articular cartilage is made of chondrocytes surrounded by their extracellular matrix that can both sense and respond to various mechanical stimuli. One of the most widely used in vitro model to study cartilage growth is the model of mesenchymal stromal cells-derived cartilage micropellet. However, mechanical stimulation of micropellets has never been reported probably because of their small size and imperfect round shape. The objective of the study was to develop an original custom-made device allowing both the mechanical stimulation and characterization of cartilage micropellets. The fluidic-based device was designed for the concomitant stimulation or characterization of six microspheres placed into the conical wells of a tank. In the present study, the device was validated using alginate-, collagen- and crosslinked collagen-based microspheres. Different types and ranges of pressure signals (square, sinusoidal and constant) were applied. The mechanical properties of microspheres were equivalent to those determined by a conventional compression test. Accuracy, repeatability and reproducibility of all types of pressure signals were demonstrated even though square signals were less accurate and sinusoidal signals were less reproducible than the others. The interest of this new device lies in the reliability to mechanically stimulate and characterize microspheres with diameters in the range of 900 to 1500 μm. Mechanical stimulation can be performed on six microspheres in parallel allowing the mechanical and molecular characterization of the same group of cartilage micropellets. The device will be useful to evaluate the growth of cartilage micropellets under mechanical stimuli.

International audience; Ecosystem fragmentation is a serious threat to biodiversity and one of the main challenges in ecosystem restoration. River continuity restoration (RCR) has often targeted diadromous fishes, a group of species supporting strong cultural and economic values and especially sensitive to river fragmentation. Yet it has frequently produced mixed results and diadromous fishes remain at very low levels of abundance. Against this background, this paper presents the main challenges for defining, evaluating and achieving effective RCR. We first identify challenges specific to disciplines. In ecology, there is a need to develop quantitative and mechanistic models to support decision making, accounting for both direct and indirect impacts of river obstacles and working at the river catchment scale. In a context of dwindling abundances and reduced market value, cultural services provided by diadromous fishes are becoming increasingly prominent. Methods for carrying out economic quantification of non-market values of diadromous fishes become ever more urgent. Given current challenges for rivers to meet all needs sustainably, conflicts arise over the legitimate use of water resources for human purposes. Concepts and methods from political science and geography are needed to develop understandings on how the political work of public authorities and stakeholders can influence the legitimacy of restoration projects. Finally, the most exciting challenge is to combine disciplinary outcomes to achieve a multidisciplinary approach to RCR. Accordingly, the co-construction of intermediary objects and diagrams of flows of knowledge among disciplines can be first steps towards new frameworks supporting restoration design and planning.

Articular cartilage is the tissue covering the surfaces of long bones ensuring smooth motions and facilitating force transmissions in joints. In the context of tissue engineering, many studies focu...

The depletion of traditional oil fields is driving the oil & gas industry to explore new exploitation sites previously considered as unprofitable. Deep-sea oil fields represent one of these new areas of exploitation. Well drilling during exploration and production operations generate large quantities of drilling waste whose biological impact on the deep-sea floor remains largely unknown. Because of the harsh abiotic factors characterizing this environment, the evaluation of this impact remains challenging. High hydrostatic pressure is the prominent factor which will affect in-situ biological processes. This review will examine the feedback on the various strategies used to evaluate the biological impact of deep-sea drilling waste deposition as well as the current technological limitations. Given the complexity of this issue, a good perspective strategy would be to trend towards the research and development of more relevant bioassays, especially considering the crucial factor of hydrostatic pressure.

International audience; The prevalence of diseases that affect the articular cartilage is increasing due to population ageing, but the current treatments are only palliative. One innovative approach to repair cartilage defects is tissue engineering and the use of mesenchymal stem/stromal cells (MSCs). Although the combination of MSCs with biocompatible scaffolds has been extensively investigated, no product is commercially available yet. This could be explained by the lack of mechanical stimulation during in vitro culture and the absence of proper and stable cartilage matrix formation, leading to poor integration after implantation. The objective of the present study was to investigate the biomechanical behaviour of MSC differentiation in micropellets, a well-defined 3D in vitro model of cartilage differentiation and growth, in view of tissue engineering applications. MSC micropellet chondrogenic differentiation was induced by exposure to TGFβ3. At different time points during differentiation (35 days of culture), their global mechanical properties were assessed using a very sensitive compression device coupled to an identification procedure based on a finite element parametric model. Micropellets displayed both a non-linear strain-induced stiffening behaviour and a dissipative behaviour that increased from day 14 to day 29, with a maximum instantaneous Young's modulus of 179.9 ± 18.8 kPa. Moreover, chondrocyte gene expression levels were strongly correlated with the observed mechanical properties. This study indicates that cartilage micropellets display the biochemical and biomechanical characteristics required for investigating and recapitulating the different stages of cartilage development.

The use of online remote control for 24/7 behavioural monitoring can play a key role in estimating the environmental status of aquatic ecosystems. Recording the valve activity of bivalve molluscs is a relevant approach in this context. However, a clear understanding of the underlying disturbances associated with behaviour is a key step. In this work, we studied freshwater Asian clams after exposure to crude oil (measured concentration, 167 ± 28 μg·L-1) for three days in a semi-natural environment using outdoor artificial streams. Three complementary approaches to assess and explore disturbances were used: behaviour by high frequency non-invasive (HFNI) valvometry, tissue contamination with polycyclic aromatic hydrocarbons (PAH), and proteomic analysis. Two tissues were targeted: the pool adductor muscles - retractor pedal muscle - cerebral and visceral ganglia, which is the effector of any valve movement and the gills, which are on the frontline during contamination. The behavioural response was marked by an increase in valve closure-duration, a decrease in valve opening-amplitude and an increase in valve agitation index during opening periods. There was no significant PAH accumulation in the muscle plus nervous ganglia pool, contrary to the situation in the gills, although the latter remained in the low range of data available in literature. Major proteomic changes included (i) a slowdown in metabolic and/or cellular processes in muscles plus ganglia pool associated with minor toxicological effect and (ii) an increase of metabolic and/or cellular processes in gills associated with a greater toxicological effect. The nature of the proteomic changes is discussed in terms of unequal PAH distribution and allows to propose a set of explanatory mechanisms to associate behaviour to underlying physiological changes following oil exposure. First, the first tissues facing contaminated water are the inhalant siphon, the mantle edge and the gills. The routine nervous activity in the visceral ganglia should be modified by nervous information originating from these tissues. Second, the nervous activity in the visceral ganglia could be modified by its own specific contamination. Third, a decrease in nervous activity of the cerebral ganglia close to the mouth, including some kind of narcosis, could contribute to a decrease in visceral ganglia activity via a decrease or blockage of the downward neuromodulation by the cerebro-visceral connective. This whole set of events can explain the decrease of metabolic activity in the adductor muscles, contribute to initiate the catch mechanism and then deeply modify the valve behaviour.

Aquatic ecosystems are subject to many anthropogenic disturbances, and understanding their possible impacts is a real challenge. Developing approaches based on the behaviour of bivalve mollusks, an integrating marker of the state of the organisms, and therefore of their environment, is relevant, whether within a natural ecosystem or an ecosystem subject to industrial activities. The main objective of this study was to identify by HFNI Valvometry a reliable and reproducible clam behavioural response in the presence of crude oil in a multistress context. To closely replicate actual field conditions, Corbicula fluminea was exposed in outdoor artificial streams that were subject to natural variations and were continuously fed by fresh water from the Gave de Pau (S.W. France). After a period of 26 days in these artificial streams, the clams (n = 14-16 per condition) were separately exposed for 10 days to crude oil alone, crude oil and barium, crude oil and noise pollution, crude oil and turbidity pulses, barium alone, noise pollution alone, turbidity pulses alone or natural changes alone. The secondary objective was to characterize the accumulation of polycyclic aromatic hydrocarbons (PAH) in 3 tissues (gills, adductor muscles and foot) in clams exposed for 10 days to crude oil alone or under multistress conditions (n = 5 clams per condition) and then to compare the accumulation and behaviour of clams under these conditions. The response of clams to crude oil alone or under multistress conditions was visually and statistically significant and not confounded by the other disturbances tested, despite large variations in water temperature. In the presence of crude oil, the behaviour of clams was characterized by an increase in valve-closure duration, a decrease in valve-opening amplitude and an increase in valve agitation index. In the presence of crude oil, the clam behaviour showed no direct relationship with PAH accumulation in the gills, adductor muscles or foot, although hypothetical mechanisms are discussed. This work supports the growing interest in studying the behaviour of bivalve mollusks in the context of biomonitoring of the aquatic environment surrounding oil facilities.

We present, for the first time, a colour coded sequence running in an endless loop and dedicated to ultra-fast Brillouin distributed sensors. Measurements within the whole elastic zone of single-mode optical fibers are presented.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. Published version available at https://doi.org/10.1016/j.marenvres.2018.09.005. The present study investigates the potential long-term physiological effects on maturing polar cod (Boreogadus saida), an Arctic key species, after an acute exposure (48 h) to environmentally realistic concentrations of either mechanically dispersed oil (MDO), chemically dispersed oil (CDO) or burned oil residues (BO) (N = 58–60 per treatment). Following exposure, fish were monitored in a common tank supplied with clean water for a seven-month period coinciding with the period of reproductive development. Females exposed to BO residues were more frequently found in an earlier phase of gonadal maturation compared to unexposed females while no effects of different oil spill response (OSR) actions were seen in the reproductive development of males. Mechanically and chemically dispersed oil induced a transient short-term reduction in growth in the first week post-exposure. Overall, no significant long-term effects of exposure were seen in growth or mortality. Ultimately, this study provides information for the assessment of population consequences of different OSR actions as part of a net environmental benefit analysis.

The high-pressure superconducting properties and the local structure of the Ba8Si46 clathrate have been studied using electrical resistance and x-ray absorption spectroscopy measurements up to more than 20 GPa. At pressures above 10–13 GPa, corresponding to a well-known volume collapse phase transformation, a sudden increase in the critical temperature leads to a maximum value of the superconducting critical temperature Tc of ∼8.5–9 K at 20 GPa. In the low-pressure clathrate phase, the superconducting critical temperature decreases as pressure is applied with an electron-phonon coupling constant λ=1.1 derived from the temperature evolution of the electrical resistance at different pressures. A progressive disorder in the Ba-Si correlations in the Ba@Si24 cages of the structure is observed for pressures beyond ∼5 GPa. These observations exclude a structural homothecy at the volume collapse transition. The high-pressure collapsed phase of Ba8Si46 is then associated with local structural changes and shows enhanced superconducting properties.

00000 ăWOS:000382802100022; International audience; Human alteration of marine ecosystems is substantial and growing. Yet, no adequate methodology exists that provides reliable predictions of how environmental degradation will affect these ecosystems at a relevant level of biological organization. The primary objective of this study was to develop a methodology to evaluate a fish's capacity to face a well-established environmental challenge, an exposure to chemically dispersed oil, and characterize the long-term consequences. Therefore, we applied high-throughput, non-lethal challenge tests to assess hypoxia tolerance, temperature susceptibility and maximal swimming speed as proxies for a fish's functional integrity. These whole animal challenge tests were implemented before (1 month) and after (1 month) juvenile European sea bass (Dicentrarchus labrax) had been acutely exposed (48 h) to a mixture containing 0.08 g L-1 of weathered Arabian light crude oil plus 4% dispersant (Corexit(C) EC9500A), a realistic exposure concentration during an oil spill. In addition, experimental populations were then transferred into semi-natural tidal mesocosm ponds and correlates of Darwinian fitness (growth and survival) were monitored over a period of 4 months. Our results revealed that fish acutely exposed to chemically dispersed oil remained impaired in terms of their hypoxia tolerance and swimming performance, but not in temperature susceptibility for 1 month post-exposure. Nevertheless, these functional impairments had no subsequent ecological consequences under mildly selective environmental conditions since growth and survival were not impacted during the mesocosm pond study. Furthermore, the earlier effects on fish performance were presumably temporary because re-testing the fish 10 months post-exposure revealed no significant residual effects on hypoxia tolerance, temperature susceptibility and maximal swimming speed. We propose that the functional proxies and correlates of Darwinian fitness used here provide a useful assessment tool for fish health in the marine environment.

$\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_{7}$ and $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{29}\mathrm{G}{\mathrm{e}}_{17}$ have been studied at high pressure using x-ray diffraction and x-ray absorption spectroscopy (XAS) at the Ge $K$ edge. In $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_{7}$, a transition is observed similar to the one in $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{46}$, apparently isostructural. However, the XAS data analysis shows that the transformation is related to the off-centering of the Ba atoms. A theoretical model based on a Landau potential suggests that this transition is second order, with a symmetry-breaking mechanism related to the Ba displacement probably initiated by the vacancy creation or local distortion predicted theoretically. This analysis gives a coherent picture of the phase transition mechanism. In the case of $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{29}\mathrm{G}{\mathrm{e}}_{17}$, such phase transition is not observed as the Ba atoms appear already off-center at ambient pressure.

From initial calcium aluminosilicate glass, transparent glass-ceramics have been successfully synthesized under simultaneous high pressure and temperature (SHPT). Possible homogeneous volumetric crystallization of this glassy system, which was not achieved previously by means of conventional heat treatment, has been put in evidence with a SHPT procedure. Structural, mechanical, and optical properties of glass and glass-ceramic obtained were investigated. Raman spectroscopy and X-ray diffraction allowed to identify two main crystalline phases: merwinite [Ca3Mg(SiO4)2] and diopside [CaMgSi2O6]. A Raman scanning profile showed that the formation of merwinite is quite homogeneous over the bulk sample. However, the sample surface also contains significant diopside crystals. Instrumented Berkovich nanoindentation was applied to determine the effect of SHPT on hardness from glass to glass-ceramic. For Eu-doped samples, the broadband emission due to 4f65d1 → 4f7 transition of Eu2+ was studied in both host systems. Additionally, the 5D0 → 7FJ transition of Eu3+ was used as an environment probe in the pristine glass and the glass-ceramic.

We describe a setup to carry out electronic transport measurements under high pressures on individual nano-objects. It is based on a home-automated three-stage gas compressor working with argon or helium up to 1 GPa. The setup was successfully tested on contacted individual nanotubes, for which we evidence strong evolutions of the transport properties. These evolutions are related to fundamental issues such as the modification of the nano-object contact resistance, the pressure-induced modification of the nano-object geometry or pressure-induced changes in the intrinsic electronic properties of the nanosystem. A cryostat has also been adapted to the pressure cell, allowing combined pressure and temperature experiments down to 12 K.

International audience; The aim of this study was to evaluate the effects of chemically dispersed oil on an economically and ecologically important species inhabiting coasts and estuaries, the Pacific oyster Crassostrea gigas. Studies were carried out with juveniles, known to generally be more sensitive to environmental stress than adults. A set of enzyme activities involved in immune defence mechanisms and detoxification processes, i.e. superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx), catecholase-type phenoloxidase (PO), laccase-type PO and lysozyme were analysed in different oyster tissues, i.e. the gills, digestive gland and mantle, and in the plasma and the haemoycte lysate supernatant (HLS) of the haemolymph. Results indicated that total PAH body burdens were 2.7 times higher in the presence than in the absence of the chemical dispersant. After 2 days of exposure to chemically dispersed oil, alkylated naphthalenes accounted for 55% of the total PAH body burden, whereas alkylated fluorenes and alkylated dibenzothiophenes accounted for 80% when the chemical dispersant was absent. Importantly, a higher number of enzyme activities were modified when oil was chemically dispersed, especially in the plasma and gills. Moreover, independently of the presence or absence of chemical dispersant, oil exposure generally inhibited enzyme activities in the gills and plasma, while they were generally activated in the mantle and haemocytes. These results suggest that the gills and plasma constitute sensitive compartments in C. gigas, and that mantle and haemocytes may play an important role in protection against xenobiotics. Among the six enzyme activities that were analysed in these body compartments, five were modulated in the chemical dispersion (CD) treatment while only half of the enzyme activities were modulated in the mechanical dispersion treatment. Furthermore, CD treatment effects were often observed following exposure, but also during depuration periods. These results suggest that immune and/or detoxification responses are likely to be affected when dispersants are used to treat oil spills in shallow waters.

International audience; High pressure and high temperature experiments were performed on single-wall carbon nanotube bundles up to 14.5 GPa and 1800 K. Depending on the thermodynamic conditions, we have observed three different behaviors: at ambient temperature and for pressure lower than 24 GPa, minor structural changes are observed. Depending on the loss of hydrostatic conditions or on the combined application of pressure and temperature, partial or total graphitization is observed. For pressures of 14.5 GPa and temperatures of 1800 K the nanotubes are irreversibly transformed into cubic diamond, showing that it is possible to synthesize under high pressure and high temperature pure sp3 carbon structures from single-wall carbon nanotubes. In the case of iodine intercalated nanotubes, the same conditions of 14.5 GPa and 1800 K lead also to the transformation into diamond. No evidence of incorporation of iodine in the sp3 carbon structure was found. On the basis of our results, we discuss possibilities for new carbon–carbon composite engineering from single-wall carbon nanotube bundles.

X-ray diffraction measurements have been performed on Rb6C60 and Cs6C60 compounds at a constant pressure around 5 GPa as a function of temperature. The data show the occurrence of an irreversible t...

International audience; The in vitro effects of polycyclic aromatic hydrocarbons (PAHs) on two plasmatic immune parameters, lysozyme concentration and haemolytic alternative complement activity, of the European sea bass, Dicentrarchus labrax, were tested using field (10(-7) and 10(-9) mg mL(-1)) and high concentrations (10(-3) and 10(-5) mg mL(-1)) observed during oil spills. Peripheral blood from 105 fish was collected, centrifuged at 1200 g, for 10 min, at 4 degrees C and three plasma pools, each of 35 fish, were constituted. Two oils (heavy fuel oil and light cycle oil) and 16 pure PAHs, selected on the basis of the American Environmental Protection Agency list (US EPA), were tested in vitro on the two humoral immune parameters. Only three pure PAHs (anthracene, chrysene and dibenz[a,h]anthracene) modulated lysozyme concentration. Acenaphthene, acenaphthylene, anthracene, benzo[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, pyrene and light cycle oil modified the haemolytic alternative complement activity after 4h of incubation. This study investigates the direct effects of several PAHs on fish humoral immune functions and describes the haemolytic complement activity of fish as suitable biomarkers of oil pollution.

Densified silica can be obtained by different pressure and temperature paths and for different stress conditions, hydrostatic or including shear. The density is usually the macroscopic parameter used to characterize the different compressed silica samples. The aim of our present study is to compare structural modifications for silica glass, densified from several routes. For this, densified silica glasses are prepared from cold and high temperature (up to 1020 °C) compressions. The different densified glasses obtained in our study are characterized by micro-Raman spectroscopy. Intertetrahedral angles from the main band relative to the bending mode decrease and their values are larger for densified samples from high temperature compression than those samples from cold compression. The relative amount of 3-membered rings deduced from the D2 line area increases as a function of density for cold compression. The temperature increase during the compression process induces a decrease of the 3 fold ring population. Moreover, 3 fold rings are more deformed and stressed for densified samples at room temperature at the expense of those densified at high temperature. Temperature plays a main role in the reorganization structure during the densification and leads to obtaining a more relaxed structure with lower stresses than glasses densified from cold compression. The role of hydrostatic or non-hydrostatic applied stresses on the glass structure is discussed. From the Sen and Thorpe central force model, intertetrahedral angle average value and their distribution are estimated.

International audience; We have pushed the limits of X-ray absorption spectroscopy under high pressure in order to study the stability of the Ba intercalated silicon clathrate. EXAFS experiments at the Ba K-edge have been performed in the step by step mode up to a pressure of 14.5 GPa using the Paris–Edinburgh cell with sintered diamond anvils. XANES experiments at the Ba L-III edge were done in an energy dispersive set-up using hollowed diamond anvil cells up to a pressure of 20 GPa. Combining the obtained results with high pressure X-ray diffraction we demonstrate the high stability of the Ba intercalated silicon clathrates. Our conclusions could be extended to other clathrate systems.

Injection locking of two DFB semiconductors opens new possibilities to generate effective signals for optical sensing, in order to reach better performances. Pure wave forms can be generated with qualities exceeding those obtained using external modulators. This is illustrated through the application to the distributed Brillouin sensing that shows significant progress with respect to established techniques. © 2004 IOP Publishing Ltd.

The effect of Sr chemical pressure on superconductivity was investigated in Hg2(Ba1?ySry)2YCu2O8??. The samples were synthesized at high pressure and high temperature from y = 0.0 to full substitution, y = 1.0. These Sr substituted compounds are superconducting, without Ca doping on the Y site, and show a Tc increasing with Sr, reaching 42?K for y = 1.0. A detailed neutron powder diffraction study compares the structural changes induced by this chemical Sr/Ba substitution and the mechanical pressure effects in the Hg-2212 system. It shows the strong decrease of the three Ba/Sr?O distances and consequently the shrinkage of Cu?O 1in?plane and Cu?O 2apical bonds. These structural changes, by affecting the charge transfer which occurs between the charge reservoir and the superconducting block, are responsible of the Tc enhancement with Sr content.

The effects of Sr substitution on superconductivity, and more particulary the changes induced in the hole doping mechanism, were investigated in Hg2(Ba1-ySry)2YCu2O8-d by a "bond valence sum" analysis with Sr content from y = 0.0 to y = 1.0. A comparison with CuBa2YCu2O7-d and Cu2Ba2YCu2O8 systems suggests a possible explanation of the Tc enhancement from 0 K for y = 0.0 to 42 K for y = 1.0. The charge distribution among atoms of the unit cell was determined from the refined structure, for y = 0.0 to 1.0. It shows a charge transfer to the superconducting CuO2 plane via two doping channels pi(1) and pi(2), i.e. through O2(apical)-Cu and Ba/Sr-O1 bonds respectively.

A single laser pump and probe experiment demonstrating the first very low temperature Brillouin gain spectrum measurement in standard telecommunication single-mode optical fibers at 1.55 μm is presented. A novel theoretical expression of the Brillouin gain spectrum depending on the laser sources linewidth is detailed. This makes possible measurements to extend down to a temperature of a few Kelvin where the Brillouin gain spectrum linewidth becomes equivalent to the laser source. Brillouin frequency and linewidth measurements are presented at atmospheric pressure from 1.4 to 370 K. These measurements open the way for optical fiber temperature sensors for cryogenic applications. An analytical simple modelling of non-linear Brillouin gain linewidth based on the two asymetric quantum-wells model fitting the measurements from 370 down to 20 K is presented. Measurements at ambient temperature under hydrostatic pressure equivalent to 0–2500 m water depth are presented as well.

International audience; Vermiculite materials were obtained by uniaxial pressing of potassic vermiculite powders obtained by sonication without any binder addition. The vermiculite powders, made of aggregates of particles with nanometric thick-ness and micrometric in plane dimension, were pressed in the range 17.7–80 MPa at room temperature and 200 °C, and further annealed in the range 400–800 °C. Pressing powders at 200 °C instead of 25 °C allowed the slight increase of the density of the formed materials (from 1.9 to 2 g·cm −3) due to the desorption of the water molecules from the interaggregate and interparticle spaces, allowing a higher densification. The density was also increased by tailoring the particle size distribution. The pressed materials were formed of oriented arrangement of vermiculite aggregates. The porous structure, characterized by mercury porosimetry, scanning electron microscopy, and small angle X-ray scattering, was modelled by oriented oblate spheroidal pores formed in the voids between the stacked aggregates organized in a structure possessing a cylindrical symmetry. The porous structure was found to vary with the pressure and the annealing temperature.

In this paper, we propose a new Brillouin Optical Time Domain Analysis (BOTDA) set-up that combines simultaneous Brillouin gain/loss measurements with colour coding. This technique gives the advantage that the pump power can greatly be increased, compared to other coding schemes, thus increasing the sensing range. A measurement over a 200 km fiber-loop is performed, with a 3 meter spatial resolution and an accuracy of ± 3 MHz (2σ) at the end of the sensing fiber. To the best of our knowledge, this is the best result obtained with a Brillouin sensor without Raman amplification.

National audience

We have carried out stimulated-Brillouin-scattering experiments using the pump-probe technique in a standard single-mode optical fibre for temperatures ranging from 80 to 350 K at a pump wavelength of 1.55 µm. Measurements of the internal friction and Brillouin frequency shift are given. The `tunnelling model' is used to fit our results.

Electric field gradients (EFG) on mercury sites of the Hg1201 high-Tc superconductors were measured with the perturbed angular correlation (PAC) technique. In Hg1201 samples where PAC detects higher oxygen content the EFGs have decreased to lower values indicating an elongation of the Hg-apical oxygen dumbbell. On the same samples the asymmetry parameter of the EFG becomes non-zero below 100 K, showing that the charge distribution near the Hg-apical oxygen chain becomes non-axially symmetric at low temperature.

In this experiment we investigated the synthesis of the double mercury layer compound Hg2Ba2YCu2O8-δ (Hg-2212) at 4 GPa and 900 °C by in situ x-ray diffraction performed at the high-pressure ID30 beam line at ESRF. The chemical path observed depends on the choice of the initial mixture. If one starts from a mixture of oxides and copper, an intermediate oxide phase (a high-pressure variety) containing barium and mercury is formed (we do not know if copper is present). This intermediate phase is then converted into the final Hg-2212 product. On the other hand, Hg-2212 grows directly from a pre-reacted precursor `Ba2YCu2Oy' mixed with HgO. This in situ technique clearly shows its efficiency in identifying, in real time, a phase that would have been difficult to observe ex situ.

International audience; Mercury cuprates have very interesting potential applications that have not been thoroughly explored until now because of the complexity of their synthesis. This paper presents an overview of recent results concerning their processing. At first, a simple sol-gel technique is described that permits one to easily and intimately mix the precursors. The method uses the gelification of an inorganic solution of the cations by acrylamide polymerization. Mercuration of the precursor at moderate pressures (

Electric-field gradients on mercury sites of the ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ high-${T}_{c}$ superconductor were measured with the perturbed angular correlation technique and interpreted with ab initio calculations. Under oxygen annealing, an asymmetric electric-field gradient has been assigned to the presence of single oxygen atoms, ${\mathrm{O}}_{\ensuremath{\delta}},$ which are located in the Hg planes. These experiments provide an atomic scale tool for studying charge-density variations occuring in the neighborhood of the Hg atoms, which can be induced, particularly, by pointlike defects.

Most shoreline bioremediation strategies are based on the addition of limiting nutrients to contaminated environments to cause an acceleration of the natural biodegradation process. Before approval for operational use, these products designed to be used in the environment, should be validated in field trials to assure their efficiency in reducing residual contaminant concentrations and toxicity. This paper describes the design, implementation and preliminary results of an experimental field study to evaluate the effectiveness of the bioremediation agents BIOREN 1 and BIOREN 2 of interest to the EUREKA BIOREN program. The agents BIOREN 1 and 2 are proprietary formulations of nutrients synthesised from fish meal and they were proven effective in laboratory studies of the two granular nutrient formulations. BIOREN 1 is unique in that it is augmented with a biosurfactant. To provide equivalent nitrogen concentrations the quantities of BIOREN 1 and 2 added were respectively 10 and 14.4 % of the oil quantity. T...

Melts of garnet Y 3 Al 5 O 12 and compositions lying on both sides of this compound were rapidly cooled in contactless conditions by using an aerodynamic levitation device coupled with a CO 2 laser. The crystallized phases were analyzed at room temperature by XRD and 27 Al MAS NMR. As the temperature reached by the supercooled melt decreases, the solidification was shown to lead successively to a mixture of YAlO 3 and Al 2 O 3 , a monophasic garnet type structure and a glass. The formation of Y 3 Al 5 O 12 starts at about 920 °C under the melting temperature and only 50 °C above the glass transition temperature. The solidification behaviour of liquid Y 3 Al 5− x Ga x O 12 ( x = 0.5, 1) was similar. Results clearly show the difficulties of garnet to nucleate. They are consistent with a rapid increase of the melt viscosity in the temperature range just above the formation of glass.

International audience

The formation process of high-pressure synthesized Hg-based superconductors is characterized in terms of the average copper valence (〈V Cu 〉) of the precursor. This parameter is varied by oxygen intake of non-stoichiometric phases during the precursor synthesis at specific temperature, time and cooling process treatment. The average copper valence is shown to be a controllable parameter that determines both the overall composition of the precursor and the proportion of the different phases present in it. More important, the average copper valence of the precursor seems to control the formation of a given member n of the HgBa 2 Ca n −1 Cu n O 2 n +2+δ homologous series. We find that higher precursor copper valences favor lower members of the series while higher members are only obtained with lower 〈V Cu 〉.

The Tc of the CyCu1−yBa2Ca2Cu3O8+δ (y ≈ 0.5) phase, synthesized under high pressure, has been raised from 67 K to about 120 K by heat-treatments under reducing conditions. An increase of both a and c lattice parameters occurs concomitantly with that of Tc (before: a = 3.858 (1), c = 14.766 (9) A , after: a ≈ 3.862(1), c ≈ 14.825 (3) A ). Subsequent heat-treatments under oxygen atmosphere lead, reversibly, to a decrease of Tc and of the lattice parameters. Consequently, the increase of Tc has been associated with an oxygen loss. Measurements of the resistivity under high pressure indicate that after reduction the overdoped as-prepared samples go towards the optimal doping. A structural model is proposed about the position of the mobile oxygen in the basal plane of the structure.