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

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

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

Prvo opažanje kudravog nesita Pelecanus crispus prstenovanog u Crnoj Gori u Bugarskoj

Nedavni rast gnijezdeće populacije kudravog nesita Pelecanus crispus na Skadarskom jezeru je omogućio prstenovanje većeg broja mladunaca tokom sezone gniježđenja, a time i više prijavljenih opažanja. Nalaz mlade jedinke u Bugarskoj, na udaljenosti od 540 km, predstavlja novi uvid u disperziju ove vrste, koja je nakon gnijezdeće sezone lokalizirana duž jadranske i jonske obale. Nalaz također ukazuje i na povezanost dvije razdvojene metapopulacije kudravog pelikana (mediteranske i crnomorske) u ovom dijelu areala

Prvo opažanje kudravog nesita Pelecanus crispus prstenovanog u Crnoj Gori u Bugarskoj

Nedavni rast gnijezdeće populacije kudravog nesita Pelecanus crispus na Skadarskom jezeru je omogućio prstenovanje većeg broja mladunaca tokom sezone gniježđenja, a time i više prijavljenih opažanja. Nalaz mlade jedinke u Bugarskoj, na udaljenosti od 540 km, predstavlja novi uvid u disperziju ove vrste, koja je nakon gnijezdeće sezone lokalizirana duž jadranske i jonske obale. Nalaz također ukazuje i na povezanost dvije razdvojene metapopulacije kudravog pelikana (mediteranske i crnomorske) u ovom dijelu areala

Vibrational states and disorder in continuously compressed model glasses

We present in this paper a numerical study of the vibrational eigenvectors of a two-dimensional amorphous material, previously deeply studied from the point of view of mechanical properties and vibrational eigen-frequencies [7-10]. Attention is paid here to the connection between the mechanical properties of this material in term of elastic heterogeneities (EH), and how these inherent heterogeneous structures affect the vibrational eigenvectors and their plane waves decomposition. The systems are analysed for different hydrostatic pressures, and using results from previous studies, a deeper understanding of the boson peak scenario is obtained. The vibrational spectrum of a continuously densified silica glass is also studied, from which it appears that the pulsation associated with the boson peak follows the same pressure dependence trend than that of transverse waves with pulsation associated with the EH characteristic size.Comment: 9 pages, 12 figure

Enhanced Raman Scattering of amorphous matrices for Fiber Optics Sensor

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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

Conservation traps and long‐term species persistence in human‐dominated systems

Major conservation efforts in human‐dominated systems, such as farmland, have focused on the establishment of subsidies and compensation promoting low‐impact management practices to reverse the impacts of conservation threats in the short term (reactive approaches). In this study, we discuss how a different way of framing conservation policy (proactive approaches) could lead to fundamentally different long‐term conservation outcomes. We define proactive approaches as those not necessarily including measures directly addressing the threats affecting biodiversity, but promoting transitions from current scenarios in which species are threatened to new states in which the threat is no longer present. We illustrate reactive and proactive approaches using as a case study two contrasting conservation frameworks for a vulnerable farmland bird, the Montagu's harrier (Circus pygargus ) in northeastern Spain. This example shows that reactive approaches can lead to “conservation traps,” which we defined as situations where the application of biologically focused actions in response to conservation problems results in an unsustainable need to perpetuate the implementation of those actions. Our aim is to offer a fresh perspective on biodiversity conservation in human‐dominated systems and to stimulate alternative, more holistic approaches in conservation promoting transitions to new states not requiring long‐term active and costly conservation action.This work is a contribution to the project BIONOVEL (CGL2011‐ 29539/BOS) and the project Steppeahead, funded by CSIC, Fundación General CSIC, and Banco Santander