Electron energy loss spectroscopy determination of Ti oxidation state at the (001) LaAlO3/SrTiO3 interface as a function of LaAlO3 growth conditions

At the (001) interface between the two band-insulators LaAlO3 and SrTiO3, a high-mobility electron gas may appear, which has been the object of numerous works over the last four years. Its origin is a subject of debate between the interface polarity and unintended doping. Here we use electron energy loss 'spectrum images', recorded in cross-section in a scanning transmission electron microscope, to analyse the Ti3+ ratio, characteristic of extra electrons. We find an interface concentration of Ti3+ that depends on growth conditions.Comment: 6 page

Magnetically textured y-Fe2O3 nanoparticles in a silica gel matrix: structural and magnetic properties

International audienceThis paper is devoted to magnetic and structural properties of anisotropic g -Fe2O3 superparamagnetic particles dispersed in a transparent xerogel matrix. The effect of frozen anisotropy axes and magnetic texture, induced by a magnetic field applied during the solidification of the matrix on the in-field magnetization process, is studied by alternating gradient force magnetometry and first and second order magneto-optical effects. The changes of magnetization curves with respect to the ferrofluid solution at the same particle concentration are interpreted on the basis of an existing statistical approach extended to systems with particle size distribution, which has to be taken into account for real samples. A very good agreement between the experiment and theory was achieved for a log-normal distribution of diameters which well resembles that deduced from electron microscopy observations in different imaging modes. This structural analysis states the parameter values used in calculations and confirms the relevance of basic assumptions of the model for the specimens studied. The experimental results and the related theoretical discussion should be of use to understand magnetic properties of other magnetically textured superparamagnetic system

Widespread occurrence of two carbon fixation pathways in tubeworm endosymbionts: lessons from hydrothermal vent associated tubeworms from the Mediterranean Sea

Vestimentiferan tubeworms (siboglinid polychaetes) of the genus Lamellibrachia are common members of cold-seep faunal communities and have also been found at sedimented hydrothermal vent sites in the Pacific. As they lack a digestive system, they are nourished by chemoautotrophic bacterial endosymbionts growing in a specialized tissue called the trophosome. Here we present the results of investigations of tubeworms and endosymbionts from a shallow hydrothermal vent field in the Western Mediterranean Sea. The tubeworms, which are the first reported vent-associated tubeworms outside the Pacific, are identified as Lamellibrachia anaximandri using mitochondrial ribosomal and cytochrome oxidase I gene sequences. They harbor a single gammaproteobacterial endosymbiont. Carbon isotopic data, as well as the analysis of genes involved in carbon and sulfur metabolism indicate a sulfide-oxidizing chemoautotrophic endosymbiont. The detection of a hydrogenase gene fragment suggests the potential for hydrogen oxidation as alternative energy source. Surprisingly, the endosymbiont harbors genes for two different carbon fixation pathways, the Calvin-Benson-Bassham (CBB) cycle as well as the reductive tricarboxylic acid (rTCA) cycle, as has been reported for the endosymbiont of the giant vent tubeworm Riftia pachyptila. In addition to RubisCO genes we detected ATP citrate lyase (ACL, the key enzyme of the rTCA cycle) type II gene sequences using newly designed primer sets. Comparative investigations with additional tubeworm species (Lamellibrachia luymesi, Lamellibrachia sp. 1, Lamellibrachia sp. 2, Escarpia laminata, Seepiophila jonesi) from multiple cold seep sites in the Gulf of Mexico revealed the presence of acl genes in these species as well. Thus, our study suggests that the presence of two different carbon fixation pathways, the CBB cycle and the rTCA cycle, is not restricted to the Riftia endosymbiont, but rather might be common in vestimentiferan tubeworm endosymbionts

Quantitative Analysis of Nicalon Fibres in TEM by EDXS and EELS

The global and local chemical composition of Nicalon fibres present in as-fabricated and annealed SiC-C-SiC composites are analysed by Analytical Transmission Electron Microscopy. EDXS, EELS, HREM and electron diffraction are used to characterise the fibre, which consists of different nanophases containing carbon, oxygen and silicon. Special attention is paid to the quantitative analysis of carbon and oxygen; different data treatment in EDXS and EELS are evaluated and compared. The limitations of the analysis techniques are discussed. The global composition of the core and the periphery of the fibre in the as-fabricated composite is determined to be: 57.5 wt% Si, 29 wt% C, 13.5 wt% O (38.6at% Si, 45.5at% C, 15.9at% O) and 53 wt% Si, 32 wt% C, 15 wt% O (34.4at% Si, 48.5at% C, 17.1at% C), respectively. After annealing in atmospheres with different oxygen partial pressures, the global oxygen content in the (fibre changes. The fibre constituents are silicon carbide nanocrystals, graphite units and an amorphous silicon oxycarbide phase.La composition chimique de fibres Nicalon dans des composites SiC-C-SiC bruts de fabrication et recuits est étudié en Microscopie Electronique en Transmission. Les modes analytiques EDX et EELS, complétés par l'imagerie haute résolution et la diffraction électronique sont utilisés pour caractériser les fibres constituées de nanophases contenant du carbone, de l'oxygène et du silicium. Une attention particulière est portée sur l'analyse quantitative du carbone et de l'oxygène pour laquelle différentes méthodes de traitement sont évaluées et comparées. Les limites des techniques employées sont discutées. Le coeur de la fibre et sa périphérie dans le matériau brut de fabrication sont composées respectivement de 57.5 % de silicium (38.6 %at), 29 % de carbone (45.5 %at), 13.5 % d'oxygène (15.9 %at) et de 53 % de silicium (34.4 %at), 32 % de carbone (48.5 %at) et de 15 % d'oxygène en concentration massique relative (17.1 %at). La concentration relative d'oxygène dans la fibre évolue pendant les recuits sous différentes pressions partielles d'oxygène. La fibre est constituée de nanocristaux de SiC, de carbone turbostratique et d'une phase oxycarbure amorphe

Study of 0.9PMN–0.1PT Dielectric Behaviour in Relation to the Nanostructure

International audience(1 - x)PbMg1/3Nb2/3O3-xPbTiO3 ceramics with x = 0, 0.1 were prepared with a 12 mol% MgO excess to obtain dense and perovskite phase materials after sintering. The dielectric characterization has revealed that a local polarization appears at a Td temperature largely above the temperature of the maximum of permittivity (Tm, respectively -13 ○C and +36 ○C for x = 0 and 0.1). This phenomena is consistent with the nucleation of polar clusters. Moreover, a dielectric relaxation is observed for 0.9PMN-0.1PT-0.12MgO, in a large frequency range (100 Hz – 1 GHz), which corresponds to a multi-Debye process with broadening of the relaxation time distribution as the temperature decreases. This suggests a nucleation and growth mechanism of polar clusters with decreasing temperature, which can result from the successive transitions of different compositions. This hypothesis was confirmed by the identification of large chemical heterogeneities on a nanometric scale by TEM using two spectroscopy techniques (EDXS and EELS), because of the association of low and high atomic number elements in the materials, different types of equipment and also the simulation of the patterns with standards. In fact, these quantitative analyses have revealed large fluctuations of the local composition around the nominal one: lead and magnesium deficient areas enriched in niobium coexist with nanodomains largely enriched in lead and slightly in magnesium, which the size depends on the titanium content. The origin of these heterogeneities in correlation with the reactions sequences during calcination and sintering is discussed: in particular the addition of titanium contributes, by stabilizing the perovskite phase, to limit the diffusion of lead oxide, which consequently increases the homogeneity of the ceramics. Due to such heterogeneities, the material remains mainly paraelectric up to very low temperatures. This effect can be balanced by the application of a high electric field which induces the growth of the polar clusters by displacement of their interface with the paraelectric matrix and orientation of their polarization in the direction of the electric field which can lead to a macroscopic ferroelectric transition in specific conditions of temperature and electric field intensity. These different mechanisms relax in a frequency range which depends on the temperature and on the amplitude of the electric field

Study of 0.9PMN–0.1PT Dielectric Behaviour in Relation to the Nanostructure

(1 - x)PbMg1/3Nb2/3O3-xPbTiO3 ceramics with x = 0, 0.1 were prepared with a 12 mol% MgO excess to obtain dense and perovskite phase materials after sintering. The dielectric characterization has revealed that a local polarization appears at a Td temperature largely above the temperature of the maximum of permittivity (Tm, respectively -13 ○C and +36 ○C for x = 0 and 0.1). This phenomena is consistent with the nucleation of polar clusters. Moreover, a dielectric relaxation is observed for 0.9PMN-0.1PT-0.12MgO, in a large frequency range (100 Hz – 1 GHz), which corresponds to a multi-Debye process with broadening of the relaxation time distribution as the temperature decreases. This suggests a nucleation and growth mechanism of polar clusters with decreasing temperature, which can result from the successive transitions of different compositions. This hypothesis was confirmed by the identification of large chemical heterogeneities on a nanometric scale by TEM using two spectroscopy techniques (EDXS and EELS), because of the association of low and high atomic number elements in the materials, different types of equipment and also the simulation of the patterns with standards. In fact, these quantitative analyses have revealed large fluctuations of the local composition around the nominal one: lead and magnesium deficient areas enriched in niobium coexist with nanodomains largely enriched in lead and slightly in magnesium, which the size depends on the titanium content. The origin of these heterogeneities in correlation with the reactions sequences during calcination and sintering is discussed: in particular the addition of titanium contributes, by stabilizing the perovskite phase, to limit the diffusion of lead oxide, which consequently increases the homogeneity of the ceramics. Due to such heterogeneities, the material remains mainly paraelectric up to very low temperatures. This effect can be balanced by the application of a high electric field which induces the growth of the polar clusters by displacement of their interface with the paraelectric matrix and orientation of their polarization in the direction of the electric field which can lead to a macroscopic ferroelectric transition in specific conditions of temperature and electric field intensity. These different mechanisms relax in a frequency range which depends on the temperature and on the amplitude of the electric field

Proliferation of purple sulphur bacteria at the sediment surface affects intertidal mat diversity and functionality

Funding provided by French National Centre for Scientific Research/INSU program EC2CO-MicroBien (Microbiologie Environnementale -BIOPOURPRE Project), European Community (ASSEMBLE grant agreement n° 227799), Region Pays de la Loire (France), Marine Alliance for Science and Technology for Scotland and the Scottish Funding Council and participating institutions.There is a relative absence of studies dealing with mats of purple sulphur bacteria in the intertidal zone. These bacteria display an array of metabolic pathways that allow them to disperse and develop under a wide variety of conditions, making these mats important in terms of ecosystem processes and functions. Mass blooms of purple sulphur bacteria develop during summer on sediments in the intertidal zone especially on macroalgal deposits. The microbial composition of different types of mats differentially affected by the development of purple sulphur bacteria was examined, at low tide, using a set of biochemical markers (fatty acids, pigments) and composition was assessed against their influence on ecosystem functions (sediment cohesiveness, CO2 fixation). We demonstrated that proliferation of purple sulphur bacteria has a major impact on intertidal mats diversity and functions. Indeed, assemblages dominated by purple sulphur bacteria (Chromatiaceae) were efficient exopolymer producers and their biostabilisation potential was significant. In addition, the massive growth of purple sulphur bacteria resulted in a net CO2 degassing whereas diatom dominated biofilms represented a net CO2 sink.Publisher PDFPeer reviewe

Bardet-Biedl syndrome highlights the major role of the primary cilium in efficient water reabsorption

Studies of the primary cilium, now known to be present in all cells, have undergone a revolution, in part, because mutation of many of its proteins causes a large number of diseases, including cystic kidney disease. Bardet–Biedl syndrome (BBS) is an inherited ciliopathy characterized, among other dysfunctions, by renal defects for which the precise role of the cilia in kidney function remains unclear. We studied a cohort of patients with BBS where we found that these patients had a urinary concentration defect even when kidney function was near normal and in the absence of major cyst formation. Subsequent in vitro analysis showed that renal cells in which a BBS gene was knocked down were unciliated, but did not exhibit cell cycle defects. As the vasopressin receptor 2 is located in the primary cilium, we studied BBS-derived unciliated renal epithelial cells and found that they were unable to respond to luminal arginine vasopressin treatment and activate their luminal aquaporin 2. The ability to reabsorb water was restored by treating these unciliated renal epithelial cells with forskolin, a receptor-independent adenylate cyclase activator, showing that the intracellular machinery for water absorption was present but not activated. These findings suggest that the luminal receptor located on the primary cilium may be important for efficient transepithelial water absorption

Epidural analgesia in critically ill patients with acute pancreatitis: the multicentre randomised controlled EPIPAN study protocol

BACKGROUND: Acute pancreatitis (AP) is associated with high morbidity and mortality in its most severe forms. Most patients with severe AP require intubation and invasive mechanical ventilation, frequently for more than 7 days, which is associated with the worst outcome. Recent increasing evidence from preclinical and clinical studies support the beneficial effects of epidural analgesia (EA) in AP, such as increased gut barrier function and splanchnic, pancreatic and renal perfusion, decreased liver damage and inflammatory response, and reduced mortality. Because recent studies suggest that EA might be a safe procedure in the critically ill, we sought to determine whether EA reduced AP-associated respiratory failure and other major clinical outcomes in patients with AP. METHODS AND ANALYSIS: The Epidural Analgesia for Pancreatitis (EPIPAN) trial is an investigator-initiated, prospective, multicentre, randomised controlled two-arm trial with assessor-blinded outcome assessment. The EPIPAN trial will randomise 148 patients with AP requiring admission to an intensive care unit (ICU) to receive EA (with patient-controlled epidural administration of ropivacaine and sufentanil) combined with standard care based on current recommendations on the treatment of AP (interventional group), or standard care alone (reference group). The primary outcome is the number of ventilator-free days at day 30. Secondary outcomes include main complications of AP (eg, organ failure and mortality, among others), levels of biological markers of systemic inflammation, epithelial lung injury, renal failure, and healthcare-associated costs. ETHICS AND DISSEMINATION: The study was approved by the appropriate ethics committee (CPP Sud-Est VI). Informed consent is required. If the combined application of EA and standard care proves superior to standard care alone in patients with AP in the ICU, the use of EA may become standard practice in experienced centres, thereby decreasing potential complications related to AP and its burden in critically ill patients. The results will be disseminated in a peer-reviewed journal. TRIAL REGISTRATION NUMBER: NCT02126332