Experimental study on the cyclic resistance of a natural loess from Northern France

In order to analyze the instability phenomenon observed along the Northern High Speed Line of R\'eseau Ferr\'e de France (RFF), soil blocks were taken at a site near the railway, at four different depths (1.2, 2.2, 3.5 and 4.9 m). Cyclic triaxial tests were carried out on saturated and unsaturated soil specimens. The results from tests on initially saturated specimens showed that the soil taken at 2.2 m depth has the lowest resistance to cyclic loading, in relation to its highest porosity and lowest clay fraction. This soil was then studied at unsaturated state with various initial water contents. Unsaturated soil specimens were first subjected to cyclic loadings to decrease their volume. These cyclic loadings was stopped when the volume decrease was approximately equal to the initial pore air volume, or when the pores filled by air were eliminated and the soil was considered to become saturated. Afterwards, the back-pressure tubing was saturated with de-aired water and cycles were applied under undrained condition. Significant effect of initial water content was evidenced: the lower the initial water content, the higher the cyclic resistance. This can be explained by the densification of the soil during the initial cyclic loadings

The influence of changes in water content on the electrical resistivity of a natural unsaturated loess

Non-destructive methods of measuring water content in soils have been extensively developed in the last decades, especially in soil science. Among these methods, the measurements based on the electrical resistivity are simple and reliable thanks to the clear relationship between the water content and the electrical resistivity of soils. In this work, a new electrical resistivity probe was developed to monitor the change in local water content in the triaxial apparatus. The probe is composed of two-pair of electrodes, and an electrical current is induced through the soil at the vicinity of the contact between the probe and the specimen. Some experimental data on the changes in resistivity with the degree of saturation were obtained in specimens of a natural unsaturated loess from Northern France. Two theoretical models of resistivity were also used to analyze the obtained data. Results are finally discussed with respect to the loess's water retention properties

On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils

To provide a complete local monitoring of the state of an unsaturated soil sample during triaxial testing, a local water content measurement device was adapted to a triaxial device comprising the measurement of local displacements (Hall effect transducers) and suction (High capacity transducer). Water content was locally monitored by means of a resistivity probe. The water content/resistivity calibration curves of an intact natural unsaturated loess from Northern France extracted by block sampling at two depths (1 and 3.3 m) were carefully determined, showing good accuracy and repeatability. The validity of two models giving the resistivity of unsaturated soils with respect to their water content was examined

Evolution of AQL X-1 During the Rising Phase of its 1998 Outburst

We present results from 16 snapshots of Aql X-1 with RXTE during the rising phase of its recent outburst. The observations were carried out at a typical rate of once or twice per day. The source shows interesting spectral evolution during this period. Phenomenologically, it bears remarkable similarities to ``atoll'' sources. Shortly after the onset of the outburst, the source is seen to be in an ``island'' state, but with little X-ray variability. It then appears to have made a rapid spectral transition (on a time scale less than half a day) to another ``island'' state, where it evolves slightly and stays for 4 days. In this state, the observed X-ray flux becomes increasingly variable as the source brightens. Quasi-period oscillation (QPO) in the X-ray intensity is detected in the frequency range 670--870 Hz. The QPO frequency increases with the X-ray flux while its fractional rms decreases. The QPO becomes undetectable following a transition to a ``banana'' state, where the source continues its evolution by moving up and down the ``banana'' branch in the color-color diagram as the flux (presumably, the mass accretion rate) fluctuates around the peak of the outburst. Throughout the entire period, the power density spectrum is dominated by very-low frequency noises. Little power can be seen above ~1 Hz, which is different from typical ``atoll'' sources. In the ``banana'' state, the overall X-ray variability remains low (with fractional rms ~3--4%) but roughly constant. The observed X-ray spectrum is soft with few photons from above $\sim$25 keV, implying the thermal origin of the emission. The evolution of both spectral and temporal X-ray properties is discussed in the context of disk-instability models.Comment: 13 pages, including one table and five figures. To appear in ApJ Letters (July 20

The water retention properties of a natural unsaturated loess from Northern France

International audienceThe water retention properties of a natural loess from Northern France were investigated on intact block samples that were excavated along a high speed train line (TGV) that experienced stability problems during heavy rain episodes. Suction measurements were made by using the filter paper method and a home made high capacity tensiometer (HCT) so as to determine the water retention curve of the loess. The results showed that an alternative approach using a previously wetted filter paper could fruitfully be used with suction values fairly compatible with the HCT measurements. The water retention curve obtained exhibited a peculiar form with no hysteresis observed around the natural water content (14.4%) and two hysteresis loops on both the wet and dry sides of the curve. This zone with no hysteresis is supposed to correspond to the natural variations of the water content under seasonal changes, providing a range of natural suction between 20 and 80 kPa that should obviously checked by in-situ measurements. The loess microstructure was investigated by using scanning electron microscope and mercury intrusion porosimetry. It appeared that the clay fraction (16%) was not uniformly distributed with some areas composed of clean grains and a well graded corresponding inter-grains pore population. Conversely, the clay aggregations define a smaller sized porosity. The calculation of a water retention curve derived from the pore size distribution curve showed that water retention is governed by capillarity in the largest pores between clean grains whereas clay adsorption becomes dominant in smallest pores, a zone where the microstructure is sensitive to change in water content

Some aspects of the compression and collapse behaviour of an unsaturated natural loess

International audienceThe compression and collapse behaviour of a natural unsaturated loess from Northern France was investigated by running a series of constant rate of strain oedometric compression tests (together with some step loading tests) while monitoring suction by means of a high capacity tensiometer. The reasonably constant suction measured during constant water compression tests was linked to the collapse of the largest dry pores. Time dependent behaviour was also observed, with different responses obtained at different strain rates. In a standard fashion, collapse tests appeared to bring the representative point from the constant water content curve to the zero suction compression curve, indicating the existence of a maximum collapse stress. Data were qualitatively interpreted by using the Loading Collapse (LC) yield curve of the Barcelona basic model. Changes in the LC yield curve inclinations could account for the existence of a maximum collapse value

Structural Characterization of the ICOS/ICOS-L Immune Complex Reveals High Molecular Mimicry by Therapeutic Antibodies

The inducible co-stimulator (ICOS) is a member of the CD28/B7 superfamily, and delivers a positive co-stimulatory signal to activated T cells upon binding to its ligand (ICOS-L). Dysregulation of this pathway has been implicated in autoimmune diseases and cancer, and is currently under clinical investigation as an immune checkpoint blockade. Here, we describe the molecular interactions of the ICOS/ICOS-L immune complex at 3.3 Ao resolution. A central FDPPPF motif and residues within the CC' loop of ICOS are responsible for the specificity of the interaction with ICOS-L, with a distinct receptor binding orientation in comparison to other family members. Furthermore, our structure and binding data reveal that the ICOS N110 N-linked glycan participates in ICOS-L binding. In addition, we report crystal structures of ICOS and ICOS-L in complex with monoclonal antibodies under clinical evaluation in immunotherapy. Strikingly, antibody paratopes closely mimic receptor-ligand binding core interactions, in addition to contacting peripheral residues to confer high binding affinities. Our results uncover key molecular interactions of an immune complex central to human adaptive immunity and have direct implications for the ongoing development of therapeutic interventions targeting immune checkpoint receptors. The inducible co-stimulator (ICOS) is a member of the CD28/B7 superfamily, binding its ligand (ICOS-L) on activated T cells. The structure of the ICOS/ICOS-L complex reveals a distinct receptor binding orientation. The structures of ICOS and ICOS-L in complex with potentially therapeutic antibodies suggest the structural basis of such antibodies' efficacies and high binding affinities.This work was supported by the European Union's Horizon 2020 research and innovation program under Marie Sklodowska-Curie grant 790012 (E.R.), by operating grant PJT-148811 from the Canadian Institutes of Health Research (J.P.J.), the CIFAR Azrieli Global Scholar program (J.P.J.), the Ontario Early Researcher Awards program (J.P.J.), and the Canada Research Chairs program (J.P.J.). T.S. is a recipient of a Vanier Canada Graduate Scholarship. The BLI instrument was accessed at the Structural & Biophysical Core Facility, The Hospital for Sick Children, supported by the Canada Foundation for Innovation and Ontario Research Fund. X-ray diffraction experiments were performed at GM/CA@APS, which has been funded in whole or in part with federal funds from the National Cancer Institute (ACB-12002) and the National Institute of General Medical Sciences (AGM -12006). The Eiger 16M detector at GM/CA-XSD was funded by NIH grant S10 OD012289. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science user facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE-ACO2-06CH11357. X-ray diffraction experiments were also performed at the NSLS-II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by BNL under Contract No. DE -5C0012704. The Life Science Biomedical Technology Research resource is primarily supported by the National Institute of Health, National Institute of General Medical Sciences (NIGMS) through a Biomedical Technology Research Resource P41 grant (P41GM111244), and by the DOE Office of Biological and Environmental Research (KP1605010)

Suction measurements on a natural unsaturated soil: A reappraisal of the filter paper method

International audienceSoil suction measurements on an unsaturated soil were performed using the filter paper method and a high capacity tensiometer so as to analyse the reliability of the filter paper technique. The results show that an alternative approach of the filter paper method based on using a previously wetted filter paper can fruitfully be used to measure suction provided an appropriated calibration curve is used. This method was compared to the standard filter paper method in which the paper is initially dry and a good agreement was found between the two approaches, being the “wet” method somewhat faster in terms of suction equilibration. Suction data also agree well with results obtained independently using a home made high capacity tensiometer. The two methods finally provide a first outlook of the water retention properties of an unsaturated loess from Northern France, observing some evidences of hydraulic hysteresis on it