115 research outputs found
Influence of thermal history on the structure and properties of silicate glasses
We studied a set of float glass samples prepared with different fictive
temperature by previous annealing around the glass transition temperature. We
compared the results to previous measurements on a series of amorphous silica
samples, also prepared with different fictive temperature. We showed that the
modifications on the structure at a local scale are very small, the changes of
physical properties are moderate but the changes on density fluctuations at a
nanometer scale are rather large: 12 and 20% in float glass and silica, for
relative changes of fictive temperature equal to 13 and 25% respectively. Local
order and mechanical properties of silica vary in the opposite way compared to
float glass (anomalous behavior) but the density fluctuations in both glasses
increase with temperature and fictive temperature
In situ measurements of density fluctuations and compressibility in silica glass as a function of temperature and thermal history
In this paper, small-angle X-ray scattering measurements are used to
determine the different compressibility contributions, as well as the
isothermal compressibility, in thermal equilibrium in silica glasses having
different thermal histories. Using two different methods of analysis, in the
supercooled liquid and in the glassy state, we obtain respectively the
temperature and fictive temperature dependences of the isotheraml
compressibility. The values obtained in the glass and supercooled liquid states
are very close to each other. They agree with previous determinations of the
literature. The compressibility in the glass state slightly decreases with
increasing fictive temperature. The relaxational part of the compressibility is
also calculated and compared to previous determinations. We discussed the small
differences between the different determinations
Density hardening plasticity and mechanical aging of silica glass under pressure: A Raman spectroscopic study
In addition of a flow, plastic deformation of structural glasses (in
particular amorphous silica) is characterized by a permanent densification.
Raman spectroscopic estimators are shown to give a full account of the plastic
behavior of silica under pressure. While the permanent densification of silica
has been widely discussed in terms of amorphous-amorphous transition, from a
plasticity point of view, the evolution of the residual densification with the
maximum pressure of a pressure cycle can be discussed as a density hardening
phenomenon. In the framework of such a mechanical aging effect, we propose that
the glass structure could be labelled by the maximum pressure experienced by
the glass and that the saturation of densification could be associated with the
densest packing of tetrahedra only linked by their vertices
Enhanced Raman Scattering of amorphous matrices for Fiber Optics Sensor
International audienc
New Mechanism for Electronic Energy Relaxation in Nanocrystals
The low-frequency vibrational spectrum of an isolated nanometer-scale solid
differs dramatically from that of a bulk crystal, causing the decay of a
localized electronic state by phonon emission to be inhibited. We show,
however, that an electron can also interact with the rigid translational motion
of a nanocrystal. The form of the coupling is dictated by the equivalence
principle and is independent of the ordinary electron-phonon interaction. We
calculate the rate of nonradiative energy relaxation provided by this mechanism
and establish its experimental observability.Comment: 4 pages, Submitted to Physical Review
Simulation of Eu3+ luminescence spectra of borosilicate glasses by molecular dynamics calculations
Simplified inactive rare-earths doped nuclear waste glasses have been obtained by molecular dynamics (MD) simulation in order to investigate the local structure around the rare-earth by luminescence studies. MD calculations were performed with modified Born–Mayer–Huggins potentials and three body angular terms representing Coulomb and covalent interactions. Atomic positions within the glasses are then determined. Simulations of luminescence spectra were then obtained by calculation of the ligand field parameters affecting each luminescent ion. Considering the C2v symmetry, it is possible to calculate the radiative transition probabilities between the emitter level, 5D0, and the splitted receptor levels, 7FJ (J = 0–3) for each Eu3+ ion. The simulated emission spectra are obtained by convolution of all the Eu3+ ions contributions. A comparison with the experimental data issue from fluorescence line narrowing and microluminescence spectroscopies allowed us not only to validate the simulation of luminescence spectra from simulated environments, but also to confirm the presence and the identification of two major Eu3+ sites distribution in the nuclear glasses thanks to spectra-structure correlations
The future for Mediterranean wetlands: 50 key issues and 50 important conservation research questions
Wetlands are critically important for biodiversity and human wellbeing, but face a range of challenges. This is especially true in the Mediterranean region, where wetlands support endemic and threatened species and remain integral to human societies, but have been severely degraded in recent decades. Here, in order to raise awareness of future challenges and opportunities for Mediterranean wetlands, and to inform proactive research and management, we identified (a) 50 key issues that might affect Mediterranean wetlands between 2020 and 2050, and (b) 50 important research questions that, if answered, would have the greatest impact on the conservation of Mediterranean wetlands between 2020 and 2050. We gathered ideas through an online survey and review of recent literature. A diverse assessment panel prioritised ideas through an iterative, anonymised, Delphi-like process of scoring, voting and discussion. The prioritised issues included some that are already well known but likely to have a large impact on Mediterranean wetlands in the next 30 years (e.g. the accumulation of dams and reservoirs, plastic pollution and weak governance), and some that are currently overlooked in the context of Mediterranean wetlands (e.g. increasing desalination capacity and development of antimicrobial resistance). Questions largely focused on how best to carry out conservation interventions, or understanding the impacts of threats to inform conservation decision-making. This analysis will support research, policy and practice related to environmental conservation and sustainable development in the Mediterranean, and provides a model for similar analyses elsewhere in the world
Emission spectrum of V3+-αAl2O3
Two emission lines of V3+-αAl2O 3 have been obtained in the near infrared region (9 740 cm-1) at 2 K, 10 K and 77 K. Lifetimes of these lines and their behaviour under stress have been analyzed and an interpretation is suggested.Deux raies d'émission de V3+-αAl2O3 ont été mises en évidence dans le proche infra-rouge (9 740 cm-1) à 2 K, 10 K et 77 K. Leur temps de vie et leur comportement sous l'effet d'une contrainte ont été analysés et une interprétation est proposée
Addendum. Emission spectrum of v3+-αAl2o 3
No abstract availabl
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