281 research outputs found

    Colloidal brazil nut effect in sediments of binary charged suspensions

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    Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density functional theory. For deionized samples, we predict a colloidal ``brazil nut'' effect: heavy colloidal particles sediment on top of the lighter ones provided that their mass per charge is smaller than that of the lighter ones. This effect is verifiable in settling experiments.Comment: 4 pages, 4 figure

    Recent tectonic reorganization of the Nubia-Eurasia convergent 2 boundary heading for the closure of the western Mediterranean

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    : In the western Mediterranean area, after a long period (late Paleogene-Neogene) of Nubian northward subduction beneath Eurasia, subduction is almost ceased as well as convergence accommodation in the subduction zone. With the progression of Nubia-Eurasia convergence, a tectonic reorganization is therefore necessary to accommodate future contraction. Previously-published tectonic, seismological, geodetic, tomographic, and seismic reflection data (integrated by some new GPS velocity data) are reviewed to understand the reorganization of the convergent boundary in the western Mediterranean. Between northern Morocco, to the west, and northern Sicily, to the east, contractional deformation has shifted from the former subduction zone to the margins of the two backarc oceanic basins (Algerian-Liguro-Provençal and Tyrrhenian basins) and it is now active in the south-Tyrrhenian (northern Sicily), northern Liguro-Provençal, Algerian, and Alboran (partly) margins. Compression and basin inversion has propagated in a scissor-like manner from the Alboran (c. 8 Ma) to the Tyrrhenian (younger than c. 2 Ma) basins following a similar propagation of the subduction cessation and slab breakoff, i.e., older to the west and younger to the east. It follows that basin inversion is rather advanced in the Algerian margin, where a new southward subduction seems to be in its very infant stage, while it has still to properly start in the Tyrrhenian margin, where contraction has resumed at the rear of the fold-thrust belt and may soon invert the Marsili oceanic basin. GPS-derived strain rates higher in the Tyrrhenian margin than in the Algerian boundary suggest that this latter manner of contraction accommodation (contraction resumption at the rear of the orogenic wedge) is more efficient than subduction inception and basin inversion along newly-generated reverse faults (Algeria), but the differential strain rates may also be explained with the heterogeneous distribution of GPS stations. Part of the contractional deformation may have shifted toward the north in the Liguro-Provençal basin possibly because of its weak rheological properties compared with the area between Tunisia and Sardinia, where no oceanic crust occurs and seismic deformation is absent or limited compared with the adjacent strands of the Nubia-Eurasia boundary. The tectonic reorganization of the Nubia-Eurasia boundary in the study area is still strongly controlled by the inherited tectonic fabric and rheological attributes, which are both discontinuous and non-cylindrical along the boundary. These features prevent, at present, the development of long and continuous thrust faults. In an extreme and approximate synthesis, the evolution of the western Mediterranean is inferred as being similar to a Wilson Cycle in the following main steps: (1) northward Nubian subduction with Mediterranean backarc extension (since ~35 Ma); (2) progressive cessation, from west to east, of Nubian main subduction (since ~15 Ma); (3) progressive compression, from west to east, in the former backarc domain and consequent basin inversion (since ~8-10 Ma); (4) possible future subduction of former backarc basins

    The relative influences of disorder and of frustration on the glassy dynamics in magnetic systems

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    The magnetisation relaxations of three different types of geometrically frustrated magnetic systems have been studied with the same experimental procedures as previously used in spin glasses. The materials investigated are Y2_2Mo2_2O7_7 (pyrochlore system), SrCr8.6_{8.6}Ga3.4_{3.4}O19_{19} (piled pairs of Kagom\'e layers) and (H3_3O)Fe3_3(SO4_4)2_2(OH)6_6 (jarosite compound). Despite a very small amount of disorder, all the samples exhibit many characteristic features of spin glass dynamics below a freezing temperature TgT_g, much smaller than their Curie-Weiss temperature Ξ\theta. The ageing properties of their thermoremanent magnetization can be well accounted for by the same scaling law as in spin glasses, and the values of the scaling exponents are very close. The effects of temperature variations during ageing have been specifically investigated. In the pyrochlore and the bi-Kagom\'e compounds, a decrease of temperature after some waiting period at a certain temperature TpT_p re-initializes ageing and the evolution at the new temperature is the same as if the system were just quenched from above TgT_g. However, as the temperature is raised back to TpT_p, the sample recovers the state it had previously reached at that temperature. These features are known in spin glasses as rejuvenation and memory effects. They are clear signatures of the spin glass dynamics. In the Kagom\'e compound, there is also some rejuvenation and memory, but much larger temperature changes are needed to observe the effects. In that sense, the behaviour of this compound is quantitatively different from that of spin glasses.Comment: latex VersionCorrigee4.tex, 4 files, 3 figures, 5 pages (Proceedings of the International Conference on Highly Frustrated Magnetism (HFM2003), August 26-30, 2003, Institut Laue Langevin (ILL), Grenoble, France

    Structural Controls on Crustal Fluid Circulation and Hot Spring Geochemistry Above a Flat‐Slab Subduction Zone, Peru

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    Hot spring geochemistry from the Cordillera Blanca and Cordillera Huayhuash, Peru, reveal the influence of crustal‐scale structures on geothermal fluid circulation in an amagmatic region located above a flat‐slab subduction zone. To test the influence of contrasting modes of faulting in these regions, springs were targeted along the Cordillera Blanca detachment fault, within its hanging wall, in the footwall of the detachment, and in the Cordillera Huayhuash. Hot springs along the Cordillera Blanca detachment fault zone are associated with recent extension and normal faulting, and those in its footwall and the Cordillera Huayhuash are located in the Marañon fold and thrust belt where compressional structures dominate. Springs along and in the hanging wall of the Cordillera Blanca detachment fault yield brackish‐saline, alkaline‐chloride waters, with oxygen, hydrogen, carbon, and chlorine stable isotope values that suggest mixing between meteoric groundwater and saline brine affected by high water‐rock interaction. Geothermometry reservoir temperature estimates (RTEs) of 91–226°C indicate maximum flow path depths of 8.7 or 11 km, depending on geothermal gradient, associated with the Cordillera Blanca detachment fault. In contrast, springs in the footwall and in the Cordillera Huayhuash exhibit a wide range of water types with an isotopic affinity to meteoric water, suggesting a greater influence from shallow groundwater and less water‐rock interaction. For these springs, RTEs of 40–98°C correspond to much shallower circulation (1.6–4 km). Results indicate that the Cordillera Blanca detachment system accommodates significantly deeper circulation of crustal fluids compared to other regional compressional structures

    Lessons learned about the importance of raising risk awareness in the Mediterranean region (north Morocco and west Sardinia, Italy)

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    Code and data availability: The data set and software code are available at: https://doi.org/10.17605/OSF.IO/GMKYQ (Ivčević, 2021). Supplement: The supplement related to this article is available online at: https://doi.org/10.5194/nhess-21-3749-2021-supplement.Copyright © 2021 The Author(s). In order to mitigate the potentially dramatic effects of natural hazards, risk management measures are critical. However, the lack of interdisciplinary indicators and adaptable governance frameworks highlights society's vulnerability in the particular context of global environmental and climate change. This interdisciplinary research aimed at identifying reliable risk indicators and societal responses regarding natural hazards and climate change impacts to provide a governance framework for disaster risk reduction. Different societies face diverse risks and do not necessarily have the same level of local awareness of these risk. To explore the diversity of risks, two sites were selected from the Mediterranean basin, one chosen from the south coast (north Morocco) and the other from the north coast (the Italian island of Sardinia). North Morocco, a region of multi-risks, is characterised by high demographic and economic pressures; west Sardinia has remarkable biodiversity of wetlands and is characterised by high environmental and agricultural pressures, which in both cases intensify the vulnerability of the coastal areas. Testing for the local population's preparedness for future financial protection allowed for discussing the importance of risk awareness sessions or activities as an indicator of risk management. The significance of risk awareness sessions is shown in a quantitative part of the study, and its importance is also discussed with local stakeholders in north Morocco in a qualitative part of the study. It is shown that, although risk awareness sessions are recognised as important in risk management, they are not necessarily implemented. Based on these findings, further ideas on a new series of less descriptive, more dynamic and more user-friendly indicators are suggested. How can risk sessions be a dynamic indicator of a resilient society? The obtained results could serve in future governance frameworks for the mitigation of natural hazards in the Mediterranean region and more widely. Finally, the urgent need for continuous work to overcome the communication gap between the scientific community, risk administrators, civil society and the general population is emphasised.H2020 Marie SkƂodowska-Curie Actions (grant no. 713750), the Regional Council of Provence–Alpes–CĂŽte d’Azur and the Agence Nationale de la Recherche (grant nos. ANR-11-IDEX-0001-02, ANR-11-LABE-0061 and ANR-1-1E-0001-02)

    Effects on nurses' quality of working life and on patients' quality of life of an educational intervention to strengthen humanistic practice among hemodialysis nurses in Switzerland: a protocol for a mixed-methods cluster randomized controlled trial.

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    Humanistic nursing practice constitutes the cornerstone of the nursing profession. However, according to some authors, such practice tends to fade over time in favour of non-humanistic behaviours. To contrast this tendency, an educational intervention (EI) based on Watson's Theory of Human Caring was developed and tested in two pilot studies involving, respectively, rehabilitation nurses in Quebec (Canada) and haemodialysis (HD) nurses in Switzerland. In light of the positive results obtained in these, another study is being undertaken to examine more in depth the EI's effects on both HD nurses and patients in French Switzerland. The EI is expected to have positive effects on quality of nurse-patient relationship (NPR), team cohesion, nurse quality of working life (QoWL), and patient quality of life (QoL). The study described in this protocol will use a mixed-method cluster randomised controlled trial design. For the quantitative component, nurse and patient data will be collected through questionnaires. The accessible population of 135 nurses and 430 patients will be clustered into 10 HD units. These units will be randomised into an experimental group (EG) and a waiting-list control group (WLCG). Measurements will be taken at baseline (pre-intervention) and repeatedly over time (post-intervention): immediately at EI completion and six and 12 months thereafter. For the qualitative portion of the study, 18 semi-structured interviews will be conducted with EG nurses picked at random two months after EI completion to explore perceived changes in nurse humanistic practice. Qualitative data will be analysed through the relational caring inquiry method, a phenomenological approach. Descriptive and inferential statistics will be computed from the quantitative data. The study described in this protocol will determine if and how the proposed EI promotes humanistic nursing practice and how this practice affects quality of NPR, nurse QoWL, and patient QoL. Moreover, it will lay the groundwork for offering the EI to nurses in other healthcare sectors. This clinical study was registered with ClinicalTrials.gov [NCT03283891, 14/09/2017]

    Inhibiting mevalonate pathway enzymes increases stromal cell resilience to a cholesterol-dependent cytolysin

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    Animal health depends on the ability of immune cells to kill invading pathogens, and on the resilience of tissues to tolerate the presence of pathogens. Trueperella pyogenes causes tissue pathology in many mammals by secreting a cholesterol-dependent cytolysin, pyolysin (PLO), which targets stromal cells. Cellular cholesterol is derived from squalene, which is synthesized via the mevalonate pathway enzymes, including HMGCR, FDPS and FDFT1. The present study tested the hypothesis that inhibiting enzymes in the mevalonate pathway to reduce cellular cholesterol increases the resilience of stromal cells to PLO. We first verified that depleting cellular cholesterol with methyl-ÎČ-cyclodextrin increased the resilience of stromal cells to PLO. We then used siRNA to deplete mevalonate pathway enzyme gene expression, and used pharmaceutical inhibitors, atorvastatin, alendronate or zaragozic acid to inhibit the activity of HMGCR, FDPS and FDFT1, respectively. These approaches successfully reduced cellular cholesterol abundance, but mevalonate pathway enzymes did not affect cellular resilience equally. Inhibiting FDFT1 was most effective, with zaragozic acid reducing the impact of PLO on cell viability. The present study provides evidence that inhibiting FDFT1 increases stromal cell resilience to a cholesterol-dependent cytolysin
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