Photoinduced fluidity in chalcogenide glasses at low and high intensities: A model accounting for photon efficiency

International audienceDetailed measurements of photoinduced fluidity in Ge-Se glasses were performed using a novel shear relaxation test in torsion mode. It is shown that photofluidity is significant even at a very low intensity and that there is no apparent threshold for activating the photostructural processes. Instead, the mechanism of photofluidity is described as a cumulative process involving photoinduced motions of every atom within the irradiated volume. Based on this assumption, a model is proposed, which is shown to accurately predict the power and wavelength dependence of photofluidity using a single fitting parameter n. The factor n represents the photon efficiency for inducing an atomic motion. Photofluidity experiments performed on glass fibers of various mean coordination number indicate that the process is rapidly reduced in overconstrained glasses. The values of n obtained for these glasses correlate remarkably well with the mean coordination dependence of other photostructural changes (photodarkening, photoexpansion). This indicates that the model is physically sound. Moreover, the model is shown to quantitatively describe photofluidity data from other glass systems from literature, therefore suggesting that it could be universally applied to all chalcogenide glasses

Propriétés spectroscopiques des ions chrome dans différents verres et vitrocéramiques

Cette étude a pour objectif de développer des matériaux possédant de larges bandes d'absorption ou d'émission potentiellement ajustables. Plusieurs familles de verres dopés au chrome ont été synthétisées pour étudier l'influence de l'environnement chimique de ce dopant sur ses absorptions et émissions. Le premier chapitre recense le comportement optique des ions chrome avec différentes valences et nombres de coordination dans de nombreuses matrices. Le chapitre 2 explore les verres de chalcogénure dopés au chrome retrouvé sous forme de Cr et Cr . Cette dernière valence est responsable de deux bandes d'absorption centrées entre 455 et 685 nm. La bande d'émission, comme dans toutes les matrices amorphes, est attribuée à la transition interconfigurationnelle. Elle est centrée vers 1100 nm avec des durées de vie de quelques microsecondes. La céramisation de ces verres n'entraine pas d'augmentation ni de structuration de la luminescence et les ions chrome ne sont pas incorporés dans les cristaux. Le chapitre 3 étudie les ions chrome dans un environnement d'oxyfluorure. Cette variation de taille de ligands entraine un décalage des bandes d'absorption et d'émission. Les ions Cr3+ absorbent autour de 440 et 620 nm et la bande d'émission est centrée vers 880 nm. Dans une vitrocéramique, l'émission est structurée et centrée vers 740 nm. Les durées de vies sont de l'ordre de la milliseconde. Le chapitre 4 décrit des verres à base d'oxysulfure. Différents modes de synthèse ont été étudiés pour conserver le soufre dans le verre. Il a été démontré que le mode de synthèse influence significativement la valence des ions chrome qui peuvent être prioritairement sous forme de Cr + ou Cr avec des absorptions et des émissions très différentes.The objective of this study is to develop materials with potentially tunable wide absorption or emission bands. Several families of chromium doped glasses have been synthesized to study the chemical environment's impact of chromium ions on absorptions and emissions. The first chapter reviews the optical properties of chromium ions with different valences and coordination numbers in wide variety of hosts. The chapter 2 is devoted to chalcogenide glasses doped with chromium which is found mainly in Cr and Cr forms. This latest valence is responsible of two absorption bands centered at 455 and 685 nm. The emission band is centered at 1100 nm with a lifetime of a few microseconds. The crystallization of these glasses does not lead to an increase or a structuring of luminescence and chromium ions are not incorporated in crystals. The chapter 3 is on chromium ions in oxyfluoride environment. This variation of the size of ligands, compared to that of sulfide studied in chapter 2, causes a shift of absorption and emission bands towards shorter wavelengths. Cr3+ ions absorb around 440 and 620 nm and the emission band is centered at 880 nm. In a glass-ceramic, the emission is structured and centered at 740 nm. Lifetimes are in the order of milliseconds. The chapter 4 describes oxysulfide glasses. Different synthesis ways have been studied in order to conserve sulfur in the glass. It has been demonstrated that the way of synthesis significantly affects the chromium ions' valences. Chromium ions are able to be in Cr + or Cr forms with very different absorptions and emissions.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

(Methyl) Mercury, arsenic, and lead contamination of the world's largest wastewater irrigation system : the Mezquital Valley (Hidalgo State-Mexico)

In the Mezquital valley, untreated wastewater (45 m(3) s(-1)) from Mexico City is used for the irrigation of around 900 km(2) of agricultural soil. High concentrations of metals including methylmercury (3.8+/-2.5 ng l(-1)) and lead (0.16+/-0.05 mg l(-1)) were measured in anoxic wastewater canals. Downstream, dissolved, and particulate polymetallic (Hg, Pb, Cr.) concentrations decreased by factors 10 to 1,000 in the Tula River (which received a mix of fresh and wastewater) due to the dilution and oxidation of surface water, and to the decrease of contaminants concentration in wastewater downstream irrigated soils. However, dissolved and particulate methylmercury concentrations (0.06 to 0.33 ng l(-1) and 1.6 to 4.5 g kg(-1), respectively) remained elevated in comparison to other natural hydrosystems. The monitoring of an irrigation event and the distribution of metals in a soil profile irrigated for more than 80 years showed that metals were retained in the draining tilled layer. The oxic conditions and slightly acidic pH (similar to 6.5) in this layer were found favorable for metal adsorption and co-precipitation with redox-sensitive elements (Fe, Mn) and suggestively for mercury demethylation. In the downstream Tula River and groundwater, almost all metallic concentrations remained below guideline thresholds. Only, dissolved As and Pb concentrations remained two to five times above thresholds for drinking water, highlighting a potential health risk for approximately 500,000 people who use groundwater as water supply

Near-infrared down-conversion in rare-earth-doped chloro-sulfide glass GeS2-Ga2S3-CsCl: Er, Yb

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LipG a bifunctional phospholipase/thioesterase involved in mycobacterial envelope remodeling

International audienceTuberculosis caused by Mycobacterium tuberculosis is currently one of the leading causes of death from an infectious agent. The main difficulties encountered in eradicating this bacteria are mainly related to (i) a very complex lipid composition of the bacillus cell wall, (ii) its ability to hide from the immune system inside the granulomas, and (iii) the increasing number of resistant strains. In this context, we were interested in the Rv0646c (lipGMTB) gene located upstream to the mmaA cluster which is described as being crucial for the production of cell wall components and required for the bacilli adaptation and survival in mouse macrophages. Using biochemical experiments combined with the construction of deletion and overexpression mutant strains in Mycobacterium smegmatis, we found that LipGMTB is a cytoplasmic membrane-associated enzyme that displays both phospholipase and thioesterase activities. Overproduction of LipGMTB decreases the glycopeptidolipids (GPL) level concomitantly to an increase in phosphatidylinositol (PI) which is the precursor of the PI mannoside (PIM), an essential lipid component of the bacterial cell wall. Conversely, deletion of the lipGMS gene in M. smegmatis leads to an overproduction of GPL, and subsequently decreases the strain susceptibility to various antibiotics. All these findings demonstrate that LipG is involved in cell envelope biosynthesis/remodeling, and consequently this enzyme may thus play an important role in mycobacterial physiology

Mercury contamination level and speciation inventory in Lakes Titicaca and Uru-Uru (Bolivia) : current status and future trends

Aquatic ecosystems of the Bolivian Altiplano (similar to 3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and mono-methylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to similar to 50% THg from the oligoihetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high % MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota

Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends

International audienceAquatic ecosystems of the Bolivian Altiplano (∼3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to ∼50% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high %MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota

Main conclusions and perspectives from the collective scientific assessment of the effects of plant protection products on biodiversity and ecosystem services along the land–sea continuum in France and French overseas territories

International audiencePreservation of biodiversity and ecosystem services is critical for sustainable development and human well-being. However, an unprecedented erosion of biodiversity is observed and the use of plant protection products (PPP) has been identified as one of its main causes. In this context, at the request of the French Ministries responsible for the Environment, for Agriculture and for Research, a panel of 46 scientific experts ran a nearly 2-year-long (2020-2022) collective scientific assessment (CSA) of international scientific knowledge relating to the impacts of PPP on biodiversity and ecosystem services. The scope of this CSA covered the terrestrial, atmospheric, freshwater, and marine environments (with the exception of groundwater) in their continuity from the site of PPP application to the ocean, in France and French overseas territories, based on international knowledge produced on or transposable to this type of context (climate, PPP used, biodiversity present, etc.). Here, we provide a brief summary of the CSA's main conclusions, which were drawn from about 4500 international publications. Our analysis finds that PPP contaminate all environmental matrices, including biota, and cause direct and indirect ecotoxicological effects that unequivocally contribute to the decline of certain biological groups and alter certain ecosystem functions and services. Levers for action to limit PPP-driven pollution and effects on environmental compartments include local measures from plot to landscape scales and regulatory improvements. However, there are still significant gaps in knowledge regarding environmental contamination by PPPs and its effect on biodiversity and ecosystem functions and services. Perspectives and research needs are proposed to address these gaps