Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

Friction has a direct relation with the energy efficiency and environmental cleanliness in all moving mechanical systems. To develop low friction coatings is extremely beneficial for preserving not only our limited energy resources but also the earth’s environment. This study proposes a new design for low friction carbon-based nanocomposite coatings by tailoring the microstructure and phase segregation,and thereby it contributes to better controlling the mechanical and tribological properties. Experimental findings and theoretical calculations reveal that high-hardness (18.2 GPa), high-adhesion strength (28 N) as well as low-internal stress (-0.8 GPa) can be achieved by a nanocrystallite/amorphous microstructure architecture for the nc-WC/a-C(Al) carbon-based nanocomposite coating;in particular low friction (~0.05) can be acquired by creating a strong thermodynamic driving force to promote phase segregation of graphitic carbon from the a-C structure so as to form a low shear strength graphitic tribo-layer on the friction contact surfaces. This design concept is general and has been successfully employed to fabricate a wide class of low friction carbon-based nanocomposite coating

Circulating adrenomedullin estimates survival and reversibility of organ failure in sepsis: the prospective observational multinational Adrenomedullin and Outcome in Sepsis and Septic Shock-1 (AdrenOSS-1) study

Background: Adrenomedullin (ADM) regulates vascular tone and endothelial permeability during sepsis. Levels of circulating biologically active ADM (bio-ADM) show an inverse relationship with blood pressure and a direct relationship with vasopressor requirement. In the present prospective observational multinational Adrenomedullin and Outcome in Sepsis and Septic Shock 1 (, AdrenOSS-1) study, we assessed relationships between circulating bio-ADM during the initial intensive care unit (ICU) stay and short-term outcome in order to eventually design a biomarker-guided randomized controlled trial. Methods: AdrenOSS-1 was a prospective observational multinational study. The primary outcome was 28-day mortality. Secondary outcomes included organ failure as defined by Sequential Organ Failure Assessment (SOFA) score, organ support with focus on vasopressor/inotropic use, and need for renal replacement therapy. AdrenOSS-1 included 583 patients admitted to the ICU with sepsis or septic shock. Results: Circulating bio-ADM levels were measured upon admission and at day 2. Median bio-ADM concentration upon admission was 80.5 pg/ml [IQR 41.5-148.1 pg/ml]. Initial SOFA score was 7 [IQR 5-10], and 28-day mortality was 22%. We found marked associations between bio-ADM upon admission and 28-day mortality (unadjusted standardized HR 2.3 [CI 1.9-2.9]; adjusted HR 1.6 [CI 1.1-2.5]) and between bio-ADM levels and SOFA score (p < 0.0001). Need of vasopressor/inotrope, renal replacement therapy, and positive fluid balance were more prevalent in patients with a bio-ADM > 70 pg/ml upon admission than in those with bio-ADM ≤ 70 pg/ml. In patients with bio-ADM > 70 pg/ml upon admission, decrease in bio-ADM below 70 pg/ml at day 2 was associated with recovery of organ function at day 7 and better 28-day outcome (9.5% mortality). By contrast, persistently elevated bio-ADM at day 2 was associated with prolonged organ dysfunction and high 28-day mortality (38.1% mortality, HR 4.9, 95% CI 2.5-9.8). Conclusions: AdrenOSS-1 shows that early levels and rapid changes in bio-ADM estimate short-term outcome in sepsis and septic shock. These data are the backbone of the design of the biomarker-guided AdrenOSS-2 trial. Trial registration: ClinicalTrials.gov, NCT02393781. Registered on March 19, 2015

Structural transformations on vitrification in the fragile glass-forming system CaAl₂O₄

International audienceThe structure of the fragile glass-forming material CaAl 2 O 4 was measured by applying the method of neutron diffraction with Ca isotope substitution to the laser-heated aerodynamically levitated liquid at 1973(30) K and to the glass at 300(1) K. The results, interpreted with the aid of molecular dynamics simulations, reveal key structural modifications on multiple length scales. Specifically, there is a reorganization on quenching that leads to an almost complete breakdown of the AlO 5 polyhedra and threefold coordinated oxygen atoms present in the liquid, and to their replacement by a predominantly corner-sharing network of AlO 4 tetrahedra in the glass. This process is accompanied by the formation of branched chains of edge and face-sharing Ca-centered polyhedra that give cationic ordering on an intermediate length scale, where the measured coordination number for O around Ca is 6.0(2) for the liquid and 6.4(2) for the glass. Calcium aluminates ðCaOÞ x ðAl 2 O 3 Þ 1Àx (0 x 1) have been extensively studied on account of their geological , technological, and scientific importance [1-20]. For example, they are a significant component of the Earth's mantle so that the liquid structure is of interest for understanding magma-related processes [21], they are an integral component of aluminous cement [22], the glasses have a favorable infrared transmission window that extends up to a wavelength $6 m [23] giving them optical applications [24,25], and the rare-earth-metal-doped materials exhibit persistent luminescence [26]. From a glass physics perspective, calcium aluminates are very fragile glass for-mers [1,4] and, in contrast to strong network glass formers such as SiO 2 , large structural alterations should accompany the rapid change in viscosity and other dynamical properties as the glass transition temperature T g is approached [27]. Experimental information on the extent of structural transformation is therefore essential to understanding the processes occurring around T g and the material properties to which they are linked. An experimental exploration of liquid aluminates is, however, challenging because of the high temperatures involved. The containerless method of aerodynamic levitation offers a way forward, and by minimizing heterogeneous nucleation, it extends the narrow glass-forming region centered at x ¼ 0:65 in the calcium aluminate system to include the equimolar composition CaAl 2 O 4 [16] which has a fragility index of m ¼ 116 [1,28]. At this composition , the O:Al ratio is 2:1 such that it is just feasible to form an ideal network of fully connected corner-sharing AlO 4 tetrahedra where the oxygen atoms are twofold coordinated, as in the crystalline phase which has a tridymite-like structure where the tetrahedra form a fully polymerized network of six-membered rings [29]. This has motivated a range of experimental and computer simulation studies on the liquid and glass structure [2-20]. It has, however, proved difficult to measure unambiguously the Al and Ca coordination environments. For example, in the liquid state 27 Al nuclear magnetic resonance (NMR) experiments observe the fast exchange limit such that individual Al coordination environments cannot be identified [2-5], and in diffraction experiments , the nearest-neighbor Ca-O and other pair correlations are strongly overlapped [16-19]. The powerful method of neutron diffraction with isotope substitution has been used to probe directly the coordination environment of Ca in ðCaOÞ 48 ðSiO 2 Þ 49 ðAl 2 O 3 Þ 3 glass [30,31], but the method is usually limited to large samples [32]. In this Letter we show, however, that the neutron diffraction with isotope substitution method can be used to measure the detailed atomic structure of a single aerodynamically levitated laser-heated drop of liquid CaAl 2 O 4 at 1973(30) K. The structure of the glass at 300(1) K is also investigated. The results, interpreted with the aid of molecular dynamics (MD) simulations, characterize the nature of the structural transformations that occur on vitrification on both the local and intermediate atomic length scales. The total structure factor measured by neutron diffraction is given by FðQÞ ¼ P P c c b b ½S ðQÞ À 1

Corresponding States of Structural Glass Formers

The variation with respect to temperature T of transport properties of 58 fragile structural glass forming liquids (68 data sets in total) are analyzed and shown to exhibit a remarkable degree of universality. In particular, super-Arrhenius behaviors of all super-cooled liquids appear to collapse to one parabola for which there is no singular behavior at any finite temperature. This behavior is bounded by an onset temperature To above which liquid transport has a much weaker temperature dependence. A similar collapse is also demonstrated, over the smaller available range, for existing numerical simulation data.Comment: 6 pages, 2 figures. Updated References, Table Values, Submitted for Publicatio

Mercury's Interior Structure Constrained by Density and P-Wave Velocity Measurements of Liquid Fe-Si-C Alloys

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Problematic Stabilizing Films in Petroleum Emulsions: Shear Rheological Response of Viscoelastic Asphaltene Films and the Effect on Drop Coalescence

Adsorption of asphaltenes at the water-oil interface contributes to the stability of petroleum emulsions by forming a networked film that can hinder drop-drop coalescence. The interfacial microstructure can either be liquid-like or solid-like, depending on (i) initial bulk concentration of asphaltenes, (ii) interfacial aging time, and (iii) solvent aromaticity. Two techniques--interfacial shear rheology and integrated thin film drainage apparatus--provided equivalent interface aging conditions, enabling direct correlation of the interfacial rheology and droplet stability. The shear rheological properties of the asphaltene film were found to be critical to the stability of contacting drops. With a viscous dominant interfacial microstructure, the coalescence time for two drops in intimate contact was rapid, on the order of seconds. However, as the elastic contribution develops and the film microstructure begins to be dominated by elasticity, the two drops in contact do not coalescence. Such step-change transition in coalescence is thought to be related to the high shear yield stress (~10(4) Pa), which is a function of the film shear yield point and the film thickness (as measured by quartz crystal microbalance), and the increased elastic stiffness of the film that prevents mobility and rupture of the asphaltene film, which when in a solid-like state provides an energy barrier against drop coalescence