Application of molecular dynamics techniques and luminescent probes to the study of glass structure: the SiO2–GeO2 case

In this paper, we report on the results obtained from molecular dynamic simulation of a Eu3+-doped germanosilicate glass. This simulation provides further information on the structure. In particular it reveals a homogeneous distribution of SiO4 and GeO4 units, a decrease of defects compared to SiO2 and GeO2 glasses, and a trend to clustering of the doping ions. Using the modified crystal-field theory, the luminescence spectroscopic properties have been computed and comparison with experimental data has allowed a correlation of the spectral features with two main types of local environment depending on the coordination number and on the medium-range arrangement around the doping ions

Structural properties of erbium-activated silica-titania glasses: modeling by molecular dynamics method

Here, we use molecular dynamics simulation to reconstruct a silica-titania glass with a Ti/Si atomic ratio of 8.5% activated by 0.7 at% of erbium. These quantities are chosen because they give both refractive index and optically ions concentration suitable for applications. We use a modified Born-Mayer-Huggins potential taking into account a three- body interaction. The distribution of TiO4 and SiO4 units as well as the bridging to non-bridging oxygen ratios are evaluated. The local environment of rare-earth ions is also analyzed. In particular, the clustering of erbium is discussed. From the simulated structure, the crystal-field strength is computed and discussed according to the Er3+ local environment. Finally, results are compared with information obtained by Raman and photoluminescence spectra

Molecular dynamics simulation of an erbium-activated titania-silica glass: composition influence on the structural properties

We have performed molecular dynamics simulations of a TiO2–SiO2: Er3+ system for various compositions. Different distribution functions have been analysed to determine whether titanium ions are homogeneously distributed. A similar analysis has been carried out to characterize the erbium clustering ability. In particular, because of the simulation technique, the microscopic structure around erbium ions has been investigated. We discuss the role of both erbium and titanium concentrations in the structural properties of the simulated samples. For this purpose, the titanium distribution has been studied for [Ti]/[Si + Ti] concentrations ranging from 7.8 to 50% in undoped samples, and the erbium clustering trend has been characterized from three doped samples in which both erbium and titanium concentrations vary. A calculation of the crystal-field strength for the different kinds of erbium site has been interpreted in the light of the associated local structures

Modelling and simulating change in reforesting mountain landscapes using a social-ecological framework

Natural reforestation of European mountain landscapes raises major environmental and societal issues. With local stakeholders in the Pyrenees National Park area (France), we studied agricultural landscape colonisation by ash (Fraxinus excelsior) to enlighten its impacts on biodiversity and other landscape functions of importance for the valley socio-economics. The study comprised an integrated assessment of land-use and land-cover change (LUCC) since the 1950s, and a scenario analysis of alternative future policy. We combined knowledge and methods from landscape ecology, land change and agricultural sciences, and a set of coordinated field studies to capture interactions and feedback in the local landscape/land-use system. Our results elicited the hierarchically-nested relationships between social and ecological processes. Agricultural change played a preeminent role in the spatial and temporal patterns of LUCC. Landscape colonisation by ash at the parcel level of organisation was merely controlled by grassland management, and in fact depended on the farmer's land management at the whole-farm level. LUCC patterns at the landscape level depended to a great extent on interactions between farm household behaviours and the spatial arrangement of landholdings within the landscape mosaic. Our results stressed the need to represent the local SES function at a fine scale to adequately capture scenarios of change in landscape functions. These findings orientated our modelling choices in the building an agent-based model for LUCC simulation (SMASH - Spatialized Multi-Agent System of landscape colonization by ASH). We discuss our method and results with reference to topical issues in interdisciplinary research into the sustainability of multifunctional landscapes

Morphological changes of mitochondria-rich cells in gill of Sparidentex hasta during adaptation to different environmental salinities by scanning electron microscopy

To determine the cellular and adaptations changes in mitochondria-rich cells under different salinities, Sparidentex hasta as a urihaline has been studied.180 fish weighing 150 ± 0.5 gr and 23±1 cm length, were directly exposed to (5, 20, 40 and 60 ppt) salinities for a week. Sampling was performed on days 1, 2 and 7 and three fish from each tank (12 fish from each treatment) were sampled each time. Samples were fixed in glutaraldehyde 2/5 % solution and washed with 0.1M (pH=7.4) buffer phosphate. Samples were dehydrated in increasing ethanol series (from 50 % to pure ethanol) followed by 100 % acetone. Tissue blocks were frozen by liquid nitrogen and then immediately followed by scanning electron microscope LEO (Model 1455VP) with 15Kv voltage. Scanning electron microscope revealed three types of mitochondria-rich cells with derived apertures, shallow and deep apical openings. The number and size of mitochondria-rich cells in the apical openings in 60ppt salinity increased on the first day compared to rest of the treatments. During the experiment, the density and size of the openings in the mitochondria-rich cells in the lower salinity increased but in higher salinity of sea water size and density of openings decreased during experiment

Simulation by molecular dynamics of erbium-activated silica-titania glasses

Rare-earth doped silicate-based glasses are widely used in telecommunication technology. A limitation in the performance of active optical devices such as amplifier comes from the rare-earth clustering. Simulation methods give complementary informations to the spectroscopic usual investigations. We present a molecular dynamics simulation of a SiO2-TiO2:Er3+ system in varying its composition. Different distribution functions have been analyzed in order to have information about the clustering of erbium. To this purpose, the titanium distribution has been studied for concentration 7.8 and 15.7% Ti/(Ti + Si). We have simulated the structure of the system doped with 1 and 2.3 mol%. A calculation of the crystal field strength for the different kinds of erbium site has been interpreted in the light of the local structure. The important trend of erbium for clustering in our modeled system has been explained by the energetic requirements of the rare-earth

Influence of Thermal Treatment on Optical and Structure Properties of Europium-Doped SiO2–HfO2 Glasses

Eu3+-doped SiO2–HfO2 glasses for optical applications were prepared using sol–gel technology. The effect of heat treatment on structure, emission properties and decay kinetics was investigated. The results show that the energy splitting of the 7F2 state of Eu3+ ions occurs for the samples sintered at temperatures >1000°C. This behavior can be explained by the fact that crystal phases are formed in those samples, which can be confirmed by X-ray diffraction analysis. Moreover, fluorescence line narrowing spectra for the samples sintered at different temperatures were measured, and the results were interpreted in terms of structural changes in the glass matrix and the Eu3+ bonding environment

Triketone toxicity: A report on two cases of sulcotrione poisoning

INTRODUCTION: Sulcotrione is a herbicidal agent belonging to the family of triketones. Sulcotrione herbicides are used for weed control in maize and flax crops. To date, no cases of human poisoning had been reported in the literature linked to different herbicidal agents in the triketone family. We report here on two cases of the voluntary ingestion of this substance in the form of the branded product Mikado(TM), which were recorded by the Angers Poison Centre. CASE REPORT: Both cases of voluntary ingestion constituted attempted suicide, and involved two men aged 30 and 37 years. Their symptoms linked to sulcotrione were limited to vomiting, despite elevated plasma concentrations of sulcotrione. In one case, hypertyrosinemia has been demonstrated. The outcome was favourable in both patients and at follow up, no ocular disorders were observed. In the second case, hypotension and transient renal failure could be linked to the concomitant ingestion of chlorophenoxy herbicides. DISCUSSION: In animal toxicity studies, sulcotrione inhibit 4-hydro-phenylpyruvate dioxygenase leading to hypertyrosinemia and corneal opacities. In both cases, no ocular disorders were observed despite hypertyrosinemia in one case. These case reports were consistent with the animal toxicology findings concerning triketones, and particularly their relative safety in mammals following acute poisoning. However it seems prudent to monitor plasma tyrosine concentrations and to screen prospectively for corneal deposits if further acute intoxication events occur