Experimental study of D/H fractionation between water and hydrogen gas during the oxidation of Fe-bearing silicates at high temperatures (600 °C–1200 °C)

Abstract Hydrogen gas is produced during the oxidation of the FeO component of silicates by water. This redox reaction occurs during the high-temperature (400 °C–800 °C) hydrothermal alteration of oceanic crustal rocks, and is responsible for H2 production at mid-ocean ridges. Samples of international reference biotite NBS30 (δD = −65.7‰) were reacted at high temperatures (600–1200 °C) in a high-vacuum line, releasing both structural water and hydrogen gas. An apparent fractionation factor α, derived from D/H measurements of water and hydrogen gas, is linearly dependent on T−2 following the equation α = 1.024 + 2477296.T−2 with a residual standard deviation σ = 0.023. The apparent D/H fractionation factors between water vapor and hydrogen gas during biotite oxidation show a dependency on T−2 that resembles those measured either by equilibration experiments or calculated from partition functions. Moreover, the apparent fractionation factors we measured are close to those determined at equilibrium in the same temperature range by Cerrai et al. (1954). This observation suggests that the D/H fractionation between H2O and H2 could be close to equilibrium during the reduction of water to hydrogen by the FeO component of silicates

MICROSTRUCTURE OF SHEAR ZONES IN FONTAINEBLEAU SANDSTONE

On the basis of image analysis, porosity and grain-size changes have been studied inside the shear bands formed in triaxial testing on a Fontainebleau sandstone. For this rock the shear band is characterized by a white coloration visible to the naked eye. It is obtained that for specimens tested under relatively low confining pressure (7 MPa), the porosity reaches a maximal value of about 30% inside the band and decreases rapidly towards the initial value of 21% outside the band. This is interpreted as dilating shear banding at low confining pressure. For specimens tested under relatively high confining pressure (28 MPa), a different patterning is observed. A compacting zone with high grain crushing and low porosity (values between 2 and 19 %) is observed in the center of the band. This zone is surrounded by a dilating one with grain cracking and high porosity (up to 36 %). These two zones correspond to the thickness of the white coloration as observed on the sample (i.e. the shear band). This shear band is surrounded by third zone with initial porosity and healthy grains

Carbon and oxygen isotope variability among foraminifera and ostracod carbonated shells

This study investigates the effect of biological and environmental inter-individual variability on the meaning of d18O and d13C values acquired on small carbonated shells. First we present data obtained with a MultiPrep automated carbonate system on small sample sizes of a homogeneous carbonate material: Carrara marble. This demonstrates the capacities of the analytical system to reliably run small amounts of carbonates even down to 10 mg. Then we present two data sets obtained on real fossil samples of various size (sensu number of individual organisms) calibrated against the NBS19 carbonate standard. Both datasets evidence a clear trend of between-biological sample standard deviation increase for both d18O and d13C measurements when the number of pooled specimens per sample decreases. According to the results obtained from a systematic study of a geologically homogeneous sample of coeval fossil Elphidium foraminifera, we estimate that there is 95% of chances to reach between-biological sample standard deviation values higher than 1.02‰ (d18O) and 1.45‰ d13C) based on single-cell measurements. Such values are one order of magnitude higher than the instrumental standard deviations associated with these stable isotope ratios. Conversely, a minimum of 35 (d18O) and 44 (d13C) pooled specimens of Elphidium appears necessary to reach a between-sample standard deviation £ 0.25‰ with a probability of 95%. Such biological intrinsic and irreducible variability between coeval individuals, and thus samples, clearly questions the interest for single-cell analyses, more precisely, for coastal marine species, such as Elphidium, subject to many environmental changes during their life-time. Indeed, strong variations in salinity or temperature, as well as biogenic fractionation, could influence the isotopic composition of an individual specimen. Results might be less problematic for an average community including several tests. This paper underlines uncertainties linked to specific environments in which selected organisms live, especially for paleoceanographic or paleoclimatic reconstruction purposes where secular oxygen and carbon isotope variations typically range from 0.5 to 1.5‰

Systematic off-pump coronary artery revascularization in multivessel disease: Experience of three hundred cases

AbstractObjective: We sought to report our recent experience with off-pump coronary artery revascularization in multivessel disease. Methods: Between October 1996 and December 1998, 300 off-pump beating heart operations were performed at the Montreal Heart Institute by a single surgeon, representing 94% of all procedures undertaken during this same time frame (97% for 1998). This cohort of patients was compared with 1870 patients operated on with cardiopulmonary bypass from 1995 to 1996. Results: Mean age, sex distribution, and preoperative risk factors were comparable for the two groups. On average, 2.92 ± 0.8 and 2.84 ± 0.6 grafts per patient were completed in the beating heart and cardiopulmonary bypass groups, respectively. A majority of patients (70%) had either a triple or quadruple bypass. Coronary anastomoses were achieved with myocardial mechanical stabilization and heart “verticalization.” Ischemic time was shorter in the beating heart group (29.8 ± 0.9 vs 45 ± 0.4 minutes, P < .05). Similarly, the need for transfusion was significantly less in the beating heart group (beating heart operations, 34%; cardiopulmonary bypass, 66%; P < .005). Reduced use of postoperative intra-aortic counterpulsation, as well as a lower rise in creatine kinase MB isoenzyme, was observed in the beating heart group. Operative mortality rates (beating heart operations, 1.3%; cardiopulmonary bypass, 2%) and perioperative myocardial infarction (beating heart operations, 3.6%; cardiopulmonary bypass, 4.2%) were comparable for the two groups. Conclusion: In a majority of patients, off-pump complete coronary artery revascularization is an acceptable alternative to conventional operations, yielding good results given progressive experience, rigorous technique, and adequate coronary artery stabilization. (J Thorac Cardiovasc Surg 2000;119:221-9

Water weathering in rocks discontinuities

The behavior of rock discontinuities at different spatial scales remains a major challenge for scientists who want to understand the rock alteration, both in the triggering of rock-fall and in the evolution of the cliffs. Our research aim to take into account the geomorphological features related to the slopes and rock discontinuities subject to weathering conditions. Several studies show the physical effect of water in the alteration of rock through cracks and micro cracks. In Cultural Heritage point of view, a rock discontinuity could be described or analyzed as the interface between stone and joint in buildings. The mechanical and physical discontinuity behavior and its time evolution have a strong influence on the onset of instability of the blocks and on their strength. The effects of climate change (increase of rainfall, temperature fluctuation...), may significantly increase the inception of phenomena such rock falls, stone degradation and damages on monuments. The aim of this study is to characterize the chemical influence of water flowing inside the discontinuity and also through the porous stone matrix. This paper focus on experiments performed in order to analyze the effects of physical and chemical alteration on the mechanical behavior of porous limestone. Limestone is a both commonly stone used in construction of cultural heritage buildings and found on French territory. These experiments could have some interesting results in restoration or conservation of building. We'll present the results of the first two experiments performed in quasi-static and dynamic of the flowing process. The observation and the monitoring of the alteration process are performed in order to determine the physical and chemical reactions involved in this phenomenon. This one we'll be linked to the mechanical aspect of the massif and or the building

Multi-scale analysis of water alteration on the rockslope stability framework

International audienceWater is an important weathering factor on rock discontinuities and in rock mass mechanical behavior. The increase of rainfall in frequency or in intensity highlights some problems on the rock slope stability analysis. The aim of this paper is the multi scale analysis of the chemical impact of water on rock (surface roughness and matrix). In this study we show how water induces degradation and thus may decreases the stability of the discontinuous rock mass. Water is known to have significant erosion and dissolution effects on rock surface or rock matrix. The chemical features of water such as temperature, pH or salinity make it a 'good' candidate to rock degradation. This study has two main components. The first one is the study of water-solid chemical mechanisms and the other is the analysis of the mechanical response of the discontinuity modified by the water alteration. The stability of the rock mass is naturally a function of the type and the space distribution of discontinuities. The study aims also to evaluate the effect of water flow on the rock slope stability and it is performed at two space scales: laboratory (micro scale and macro scale) and in situ scales. The last one is still under investigation and will be presented

Mineral magnetic characterization of the Upper Pleniglacial Nussloch loess sequence (Germany): an insight into local environmental processes

Presently, most loess/palaeosol magnetic susceptibility records are interpreted as following either the wind-vigour model or the pedogenic enhancement model. However redoxomorphic processes induced by waterlogging, often referred to gleying in the loess literature, are also known to alter loess deposits but their impact on loess/palaeosol magnetic susceptibility records has received little attention. The reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging-induced redoxomorphic processes, thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions. The Nussloch loess-palaeosol deposit (Rhine Valley, Germany) was targeted because it is one of the best-studied Pleniglacial deposits for Western Europe in which numerous tundra gley intervals have been identified. Moreover, a comprehensive high-resolution environmental magnetism study has never been undertaken for this site. Various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition, concentration and relative magnetic grain size of the mineral magnetic assemblage. The relative changes in magnetic parameters within the investigated loess interval are primarily controlled by (1) varying concentrations of coarse-grained ferrimagnetic particles of detrital (aeolian) origin and (2) dissolution of fine-grained ferrimagnetic particles related to in situ post-depositional alteration promoted by waterlogging-induced redoxomorphic processes. Goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary (aeolian) and secondary (in situ) origin. We conclude, that redoxomorphic processes induced by waterlogging, if present, will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind-vigour and the pedogenic enhancement magnetism models

Semi-supervised learning towards automated segmentation of PET images with limited annotations: Application to lymphoma patients

The time-consuming task of manual segmentation challenges routine systematic quantification of disease burden. Convolutional neural networks (CNNs) hold significant promise to reliably identify locations and boundaries of tumors from PET scans. We aimed to leverage the need for annotated data via semi-supervised approaches, with application to PET images of diffuse large B-cell lymphoma (DLBCL) and primary mediastinal large B-cell lymphoma (PMBCL). We analyzed 18F-FDG PET images of 292 patients with PMBCL (n=104) and DLBCL (n=188) (n=232 for training and validation, and n=60 for external testing). We employed FCM and MS losses for training a 3D U-Net with different levels of supervision: i) fully supervised methods with labeled FCM (LFCM) as well as Unified focal and Dice loss functions, ii) unsupervised methods with Robust FCM (RFCM) and Mumford-Shah (MS) loss functions, and iii) Semi-supervised methods based on FCM (RFCM+LFCM), as well as MS loss in combination with supervised Dice loss (MS+Dice). Unified loss function yielded higher Dice score (mean +/- standard deviation (SD)) (0.73 +/- 0.03; 95% CI, 0.67-0.8) compared to Dice loss (p-value<0.01). Semi-supervised (RFCM+alpha*LFCM) with alpha=0.3 showed the best performance, with a Dice score of 0.69 +/- 0.03 (95% CI, 0.45-0.77) outperforming (MS+alpha*Dice) for any supervision level (any alpha) (p<0.01). The best performer among (MS+alpha*Dice) semi-supervised approaches with alpha=0.2 showed a Dice score of 0.60 +/- 0.08 (95% CI, 0.44-0.76) compared to another supervision level in this semi-supervised approach (p<0.01). Semi-supervised learning via FCM loss (RFCM+alpha*LFCM) showed improved performance compared to supervised approaches. Considering the time-consuming nature of expert manual delineations and intra-observer variabilities, semi-supervised approaches have significant potential for automated segmentation workflows

Effective stress law for the permeability of a limestone

The effective stress law for the permeability of a limestone is studied experimentally by performing constant head permeability tests in a triaxial cell with different conditions of confining pressure and pore pressure. Test results have shown that a pore pressure increase and a confining pressure decrease both result in an increase of the permeability, and that the effect of the pore pressure change on the variation of the permeability is more important than the effect of a change of the confining pressure. A power law is proposed for the variation of the permeability with the effective stress. The permeability effective stress coefficient increases linearly with the differential pressure and is greater than one as soon the differential pressure exceeds few bars. The test results are well reproduced using the proposed permeability-effective stress law. A conceptual pore-shell model based on a detailed observation of the microstructure of the studied limestone is proposed. This model is able to explain the experimental observations on the effect of the total stress and of the pore pressure on the permeability of the limestone. Effective stress coefficients for the stress-dependent permeability which are greater than one are obtained. It is shown that the controlling factor is the ratio of the different bulk moduli of the various constituents of the rock. This ratio is studied experimentally by performing microhardness tests.Comment: International Journal of Rock Mechanics and Mining Sciences (2008) In pres

SETHI / RAMSES-NG: New performances of the flexible multi-spectral airborne remote sensing research platform

International audienceSETHI is an airborne SAR/GMTI system developed by the French Aerospace Lab. ONERA, and integrating various sensors. In 2016 ONERA invested in upgrade and improvement of all SETHI components. The microwave ones cover from VHF-UHF to X Band, full polarimetric and very high resolution, along track and cross track interferometry and very high precision multi-baseline capacity for interferometry and tomography applications. The optronic sensors offer very high spatial resolution visible images and fine spectral scene analysis in VNIR and SWIR bands. This paper presents the upgrade and new performances of this flexible platform and the qualification campaign results with various sensor configurations