Resonant Raman Scattering by quadrupolar vibrations of Ni-Ag Core-shell Nanoparticles

Low-frequency Raman scattering experiments have been performed on thin films consisting of nickel-silver composite nanoparticles embedded in alumina matrix. It is observed that the Raman scattering by the quadrupolar modes, strongly enhanced when the light excitation is resonant with the surface dipolar excitation, is mainly governed by the silver electron contribution to the plasmon excitation. The Raman results are in agreement with a core-shell structure of the nanoparticles, the silver shell being loosely bonded to the nickel core.Comment: 3 figures. To be published in Phys. Rev.

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Propriétés optiques d'agrégats mixtes de métaux de transition en matrice d'alumine : Effets de taille et de composition

M. Philippe CAHUZAC, Président du jury M. Pierre LABASTIE, Rapporteur M. Patrice MELINON, M. Michel PELLARIN, M. Fabrice VALLEE, RapporteurOptical response of small noble metallic particles (Au, Ag, Cu) is dominated by a Surface Plasmon Resonance band whose position and width depend mostly on their size and on the surrounding material. This manuscript presents the study of the optical properties of bi-metallic clusters AuM (M=Ag, Ni, Co et Pt) in the diameter range 1.5-6 nm, embedded in alumina. The sample preparation and different characterisation techniques are first described. Then theoretical models are introduced to interpret optical properties. A semi-quantical approach introduces core electrons, matrix and porosity of the matrix influences, but is not really suited for all the metals studied here. In other cases, a classical model is used. The third part emphasizes the size and composition effects on the optical properties of mixed AuAg clusters. For a given relative composition, the blueshift, damping and broadening of the resonance are all the more important as the size decreases, and as the gold concentration increases. These spectra are compared with semi-quantical model calculations, based on the TDLDA formalism, including both the porosity of the matrix and an inner skin with a reduced ionic-core polarizability. Two models are introduced to describe the effective dielectric function of the ionic background in the bi-metallic clusters. We can conclude that we study alloyed AuAg clusters. At last, NiAg and CoAg are formed by a nickel or cobalt-core surrounding by a silver-shell. As predicted theoretically by classical calculations, absorption spectra present a plasmon resonance band, and, for Ni-Ag, this band actually evolves continuously from the silver one to nickel one as the nickel proportion increases. Experimentally, the plasmon band for PtAg clusters is strongly lightened which is not predicted by classical calculations neither when the dielectric function is simply expressed through those of its constituents, nor for a core-shell.La réponse optique des petites particules de métaux nobles (Au, Ag, Cu) se manifeste essentiellement par une bande de résonance plasmon de surface dont la position et la largeur dépendent notamment de la taille des agrégats et du milieu environnant. Ce travail présente l'étude des propriétés optiques d'agrégats mixtes AuM (M=Ag, Ni, Co et Pt) de 1,5 à 6 nm de diamètre, en matrice d'alumine. La technique de préparation des films minces de nanoparticules en matrice d'alumine ainsi que les différentes techniques de caractérisation et d'étude de leurs propriétés optiques sont présentées d'abord. Puis les modèles théoriques qui permettent d'interpréter ces propriétés sont introduits : un modèle semi-quantique, mettant en évidence l'influence des électrons de cœur, de la matrice et de sa porosité, mais qui n'est pas adapté à tous les systèmes; un modèle classique dans les autres cas. L'influence de la taille et de la composition des agrégats mixtes or-argent est étudiée ensuite. Les spectres d'absorption montrent une résonance plasmon de surface intermédiaire par rapport à l'argent et l'or purs, et le blue-shift observé quand la taille diminue est d'autant plus important que la proportion d'or est grande. Ces résultats expérimentaux sont comparés avec ceux d'un calcul semi-quantique, en utilisant deux modèles pour la fonction diélectrique du mélange AuAg. Il semble que ces agrégats forment plutôt des alliages. Enfin, les systèmes NiAg et CoAg forment des " core-shell " : un cœur de nickel ou de cobalt, entouré d'argent et leurs spectres d'absorption présentent une bande plasmon de surface conformément aux prévisions théoriques classiques. A l'inverse, les agrégats (PtxAg1-x)n présentent expérimentalement une résonance plasmon de surface très fortement atténuée, contrairement aux prévisions classiques si l'agrégat est sous forme " core-shell " ou a une structure pour laquelle la fonction diélectrique dépend simplement de celles de ses constituants

Atmospheric trace element concentrations in total suspended particles near Paris, France

International audienceTo evaluate today’s trace element atmospheric concentrations in large urban areas, an atmospheric survey was carried out for 18 months, from March 2002 to September 2003, in Saclay, nearby Paris. The total suspended particulate matter (TSP) was collected continuously on quartz fibre filters. The TSP contents were determined for 36 elements (including Ag, Bi, Mo and Sb) using two analytical methods: Instrumental Neutron Activation Analysis (INAA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The measured concentrations were in agreement within the uncertainties with the certified values for the polycarbonate reference material filter SRM-2783 (National Institute for Standard Technology NIST, USA). The measured concentrations were significantly lower than the recommended atmospheric concentrations. In 2003, the Pb atmospheric level at Saclay was 15 ng/m3, compared to the 500 ng/m3 guideline level and to the 200 ng/m3 observed value in 1994. The typical urban background TSP values of 1–2, 0.2–1, 4–6, 10–30 and 3–5 ng/m3 for As, Co, Cr, Cu and Sb, respectively, were inferred from this study and were compared with the literature data. The typical urban background TSP concentrations could not be realised for Cd, Pb and Zn, since these air concentrations are highly influenced by local features. The Zn concentrations and Zn/Pb ratio observed in Saclay represented a characteristic fingerprint of the exceptionally large extent of zinc-made roofs in Paris and its suburbs. The traffic-related origin of Ba, Cr, Cu, Pb and Sb was demonstrated, while the atmospheric source(s) of Ag was not identified

Inorganic Pollution in PM10 Particles Collected Over Three French Sites Under Various Influences: Rural Conditions, Traffic and Industry

International audiencePM10 particles were collected over three sites in France. The first one, Montagney was a rural site that was considered as a reference site. The second site Saclay, close to a highway, was used to study the influence of the traffic. The third site was Dunkerque, one of the most industrial areas in France for the production of steel, aluminium and petroleum refinement. More than 50 element concentrations were determined by instrumental neutron activation analysis and inductively coupled plasma–mass spectrometry. Comparisons between Saclay and Montagney shown that some elements, considered as crustal elements had similar concentration variations and weak (close to 1) enrichment factors. Elements with enrichment factors higher than 10 shown in Montagney correlated variations, with a Winter maximum, that should be due to Winter heating sources. Over Saclay, most of elements with high enrichment factors were attributed to the dense traffic of the highway. This is particularly true for Mn, Fe, Zn, Ba, Sb, Cu. Some additional elements correlated also, without a particular origin that can be ascertained. In Dunkerque, the most important industry is steel production. Correlation studies shown that Tl, Cs, Ba, Ag, Cu, Rb, Se, Mn, Pb concentration variations were closely associated to the Fe concentration variations. The second polluting industry is aluminium production. Correlation studies allowed to associate Ni, Y, Co, V, rare earth elements, Ti, Sr, Th, U, Ca, Sc, concentration variations to the aluminium concentration variations. A third important industry is petroleum refinement. The only element observed here and that is suspected to be emitted more specifically is La, used in cracking processes. An important enrichment of La with respect to Ce is observed. A strong decrease of the ratio Cl/Na was observed over the three sites, between the beginning of the experiment in Autumn 2005, and its end in Spring 2006. This was attributed to a release of gaseous HCl, produced by acidification of aerosols by other pollutants like NOx and SOx, that should have been oxidized to NO2 and SO3, then dissolved in the aerosols. The effects responsible for the loss of Cl, represents a large surface and long-term pollution event over the North of France. This work allowed a characterization of the heavy metal concentrations of the aerosol that will sustain results published in a companion paper, and that concerned the bio-accumulation of metals by Scleropodium purum, simultaneously exposed in the same sites

Heavy metal bioaccumulation by the bryophyte Scleropodium purum at three French sites under various influences: rural conditions, traffic, and industry

International audienceAn active biomonitoring of the heavy metals pollution experiment was undertaken by means of the bryophyte species Scleropodium purum transplanted at three different sites exposed to rural, traffic, or industrial influences. Concentrations of about 40 elements in S. purum were determined by instrumental neutron activation analysis and inductively coupled plasma mass spectrometry. Accumulation rates of heavy metals were determined in the three sites. These accumulation rates in polluted sites were matched together and also to those recorded at the rural site. The changes of the accumulation rate of heavy metals in S. purum versus their concentrations in PM10 particles simultaneously collected above show some different accumulation properties of S. purum according to elements and sites. S. purum has a weak efficiency in the three sites to accumulate elements like V, Cr, Cu, Zn, As, Se, Sb, and Pb originating from atmospheric hot sources generally enriched in particulates matter (PM10), whereas it is particularly high for Br, Th, and Rb. For other elements, Co, La, Ce, and Hf, and rare earth elements, Fe, Sr, Nb, Ti, Al, and Sc, the collection efficiency by S. purum is intermediate. In the industrial site Dunkerque, a magnification of the collection efficiency by S. purum for elements originating from steel and aluminum productions and petroleum refinement suggests that these metals could be enriched in coarse particles with a better accumulation by the bryophyte with respect to PM10

A fine-tuned defense at the pea root caps: Involvement of border cells and arabinogalactan proteins against soilborne diseases

International audiencePlants have to cope with a myriad of soilborne pathogens that affect crop production and food security. The complex interactions between the root system and microorganisms are determinant for the whole plant health. However, the knowledge regarding root defense responses is limited as compared to the aerial parts of the plant. Immune responses in roots appear to be tissue-specific suggesting a compartmentalization of defense mechanisms in these organs. The root cap releases cells termed root "associated cap-derived cells" (AC-DCs) or "border cells" embedded in a thick mucilage layer forming the root extracellular trap (RET) dedicated to root protection against soilborne pathogens. Pea (Pisum sativum) is the plant model used to characterize the composition of the RET and to unravel its function in root defense. The objective of this paper is to review modes of action of the RET from pea against diverse pathogens with a special focus on root rot disease caused by Aphanomyces euteiches, one of the most widely occurring and large-scale pea crop diseases. The RET, at the interface between the soil and the root, is enriched in antimicrobial compounds including defense-related proteins, secondary metabolites, and glycan-containing molecules. More especially arabinogalactan proteins (AGPs), a family of plant extracellular proteoglycans belonging to the hydroxyproline-rich glycoproteins were found to be particularly present in pea border cells and mucilage. Herein, we discuss the role of RET and AGPs in the interaction between roots and microorganisms and future potential developments for pea crop protection. KEYWORDS associated cap-derived cells (AC-DCs), Aphanomyces euteiches, arabinogalactanproteins (AGPs), root border cells, Pisum sativum, L., root defense, root extracellular trap (RET), root disease Frontiers in Plant Science frontiersin.org 0