Electron spin-lattice relaxation of Yb3+ and Gd3+ ions in glasses

The electron spin-lattice relaxation rate (T1 -1) was measured in two glass samples: (i) a phosphate glass doped with 1 wt% Yb2O3 and (ii) a Li2Si4O9 glass sample doped with 0.2 wt% Gd2O3. In the Yb3+-doped glass sample, T1, was measured by an electron-spin-echo technique from 4.2 to 6 K, by the modulation method from 10 to 26 K and by the EPR linewidth from 30 to 100 K. It was found that (T1 -1) ∝ Tn with n = 9 in the range 4.2-6 K. n decreased gradually as the temperature was increased and tended towards 2 above 40 K. Over the entire temperature range 4.2-100 K, (T1 -1) was fitted to AT + BT9J8 (ΘD/T) (where A and B are two temperature-independent constants, J8 is the well-known Van Vleck integral and ΘD is the Debye temperature). The value of ΘD (= 46.3±0.9 K) so determined is in good agreement with that of Stevens and Stapleton from their T1, measurements in the range 1.5 to 7 K. In the Gd3+-doped glass, it was observed that (T1 -1) ∝ T over the range 50-150 K. The data for Ye3+-doped glass sample were accounted for by assuming that the phonon modulation of the ligand field is the dominant mechanism, associated with a low Debye temperature in accordance with the published data obtained by using other techniques to study lattice dynamics. On the other hand, the data on the Gd3+-doped glass sample were explained to be predominantly due to a mechanism involving Two-Level-Systems (TLS). © Springer-Verlag 1996 Printed in Austria

Creative Research Science Experiences for High School Students

A French research institute raises the bar for public outreach with an educational laboratory that engages 1,000 high school students per year in mini research projects

Carbon sequestration potential and physicochemical properties differ between wildfire charcoals and slow-pyrolysis biochars

Pyrogenic carbon (PyC), produced naturally (wildfire charcoal) and anthropogenically (biochar), is extensively studied due to its importance in several disciplines, including global climate dynamics, agronomy and paleosciences. Charcoal and biochar are commonly used as analogues for each other to infer respective carbon sequestration potentials, production conditions, and environmental roles and fates. The direct comparability of corresponding natural and anthropogenic PyC, however, has never been tested. Here we compared key physicochemical properties (elemental composition, δ13C and PAHs signatures, chemical recalcitrance, density and porosity) and carbon sequestration potentials of PyC materials formed from two identical feedstocks (pine forest floor and wood) under wildfire charring- and slow-pyrolysis conditions. Wildfire charcoals were formed under higher maximum temperatures and oxygen availabilities, but much shorter heating durations than slow-pyrolysis biochars, resulting in differing physicochemical properties. These differences are particularly relevant regarding their respective roles as carbon sinks, as even the wildfire charcoals formed at the highest temperatures had lower carbon sequestration potentials than most slow-pyrolysis biochars. Our results challenge the common notion that natural charcoal and biochar are well suited as proxies for each other, and suggest that biochar’s environmental residence time may be underestimated when based on natural charcoal as a proxy, and vice versa

Monitoring biological wastewater treatment processes: Recent advances in spectroscopy applications

Biological processes based on aerobic and anaerobic technologies have been continuously developed to wastewater treatment and are currently routinely employed to reduce the contaminants discharge levels in the environment. However, most methodologies commonly applied for monitoring key parameters are labor intensive, time-consuming and just provide a snapshot of the process. Thus, spectroscopy applications in biological processes are, nowadays, considered a rapid and effective alternative technology for real-time monitoring though still lacking implementation in full-scale plants. In this review, the application of spectroscopic techniques to aerobic and anaerobic systems is addressed focusing on UV--Vis, infrared, and fluorescence spectroscopy. Furthermore, chemometric techniques, valuable tools to extract the relevant data, are also referred. To that effect, a detailed analysis is performed for aerobic and anaerobic systems to summarize the findings that have been obtained since 2000. Future prospects for the application of spectroscopic techniques in biological wastewater treatment processes are further discussed.The authors thank the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit, COMPETE 2020 (POCI-01-0145-FEDER-006684) and the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. The authors also acknowledge the financial support to Daniela P. Mesquita and Cristina Quintelas through the postdoctoral Grants (SFRH/BPD/82558/2011 and SFRH/BPD/101338/2014) provided by FCT - Portugal.info:eu-repo/semantics/publishedVersio

Synchronisation d'un interféromètre Fabry-Perot pour l'infrarouge (5,5μ à 8,5μ) et d'un spectromètre à réseau

In order to improve the performance of a grating spectrometer, we have added a Fabry-Perrot interferometer used from 5,5 μ to 8,5 μ. We have built a mechanical system to synchronize both the sweeping of the interferometer and the wavelength-pass of the grating spectrometer, for any resolving power, chosen in a wide region (the interference order can varied in the ratio from 1 to 6). We have analysed with this arotational-vibrational band of water-vapour about 7.5 μ, and we have oblained a gain between 4 and 5 for the product L.R.Afin d'améliorer les performances d'un spectromètre à réseau, nous lui avons adjoint un interféromètre Fabry-Perot, fonctionnant entre 5,5 μ et 8,5 μ. Nous avons construit un entrainement mécanique permettant de synchroniser le balayage de l'interféromètre et le défilement des longueurs d'onde du prémonochromateur quelle que soit la résolvance choisie dans un large domaine. (L'ordre d'interférence pouvant varier dans le rapport de 1 à 6). Nous avons analysé, avec cette chaine, une bande de vibration-rotation de l'eau vers 7,5 μ et nous avons obtenu un gain de 4 à 5 sur le produit L. R

État actuel des études sur la dynamique des cristaux non conducteurs

Il s’agit d’une introduction à la dynamique des cristaux non conducteurs. On examine à l’aide d’une bibliographie étendue, les « hypothèses de travail », de complexité croissante, permettant d’interpréter le comportement du cristal, tant du point de vue des vibrations « individuelles », décelées par diverses spectroscopies, que du point de vue « collectif », tel qu’il apparaît par exemple dans Je comportement thermodynamique.La confrontation avec l’expérience des théories, élaborées depuis le début du siècle, tout particulièrement par Born, permettra de passer de l’hypothèse « harmonique » (chap. II), base de toute étude, à l’approximation « quasi-harmonique » (chap. III), puis « pseudo-harmonique » et « anharmonique » (chap. IV).Seules les parties II et III, sont données, après ¡’introduction I, dans le présent article, le chapitre IV, devant être publié ultérieurement

État actuel des études sur la dynamique des cristaux non conducteurs

Cette introduction, qui traite du cristal non conducteur parfait « anharmonique » fait suite à un article A, où étaient traités les cas « harmonique » et « quasi harmonique ».On présente ici l’évolution des hypothèses sur l’anharmonicité à partir des premiers travaux de Born, et à chaque stade, une confrontation avec l'expérience. Les diverses spectroscopies (neutrons et rayonnement électromagnétique) permettent d'atteindre les modes de vibration individuels, tandis que les grandeurs thermoélastiques donnent des résultats collectifs.Les glissements de fréquence et les largeurs de raies en fonction de la température et de la pression sont en général bien interprétés dans le cas de cristaux simples, par les calculs de perturbation prenant en compte les développements en série de l’énergie potentielle; les méthodes utilisant les fonctions de Green sont particulièrement commodes.Mais si les cristaux sont très anharmoniques, la méthode « auto-cohérente », tout récemment appliquée, est mieux adaptée au traitement du problème

Electron spin-lattice relaxation of Yb3+ and Gd3+ ions in glasses

The electron spin-lattice relaxation rate (T1 -1) was measured in two glass samples: (i) a phosphate glass doped with 1 wt% Yb2O3 and (ii) a Li2Si4O9 glass sample doped with 0.2 wt% Gd2O3. In the Yb3+-doped glass sample, T1, was measured by an electron-spin-echo technique from 4.2 to 6 K, by the modulation method from 10 to 26 K and by the EPR linewidth from 30 to 100 K. It was found that (T1 -1) ∝ Tn with n = 9 in the range 4.2-6 K. n decreased gradually as the temperature was increased and tended towards 2 above 40 K. Over the entire temperature range 4.2-100 K, (T1 -1) was fitted to AT + BT9J8 (ΘD/T) (where A and B are two temperature-independent constants, J8 is the well-known Van Vleck integral and ΘD is the Debye temperature). The value of ΘD (= 46.3±0.9 K) so determined is in good agreement with that of Stevens and Stapleton from their T1, measurements in the range 1.5 to 7 K. In the Gd3+-doped glass, it was observed that (T1 -1) ∝ T over the range 50-150 K. The data for Ye3+-doped glass sample were accounted for by assuming that the phonon modulation of the ligand field is the dominant mechanism, associated with a low Debye temperature in accordance with the published data obtained by using other techniques to study lattice dynamics. On the other hand, the data on the Gd3+-doped glass sample were explained to be predominantly due to a mechanism involving Two-Level-Systems (TLS). © Springer-Verlag 1996 Printed in Austria

Electron spin-lattice relaxation of Yb3+ and Gd3+ ions in glasses

The electron spin-lattice relaxation rate (T1 -1) was measured in two glass samples: (i) a phosphate glass doped with 1 wt% Yb2O3 and (ii) a Li2Si4O9 glass sample doped with 0.2 wt% Gd2O3. In the Yb3+-doped glass sample, T1, was measured by an electron-spin-echo technique from 4.2 to 6 K, by the modulation method from 10 to 26 K and by the EPR linewidth from 30 to 100 K. It was found that (T1 -1) ∝ Tn with n = 9 in the range 4.2-6 K. n decreased gradually as the temperature was increased and tended towards 2 above 40 K. Over the entire temperature range 4.2-100 K, (T1 -1) was fitted to AT + BT9J8 (ΘD/T) (where A and B are two temperature-independent constants, J8 is the well-known Van Vleck integral and ΘD is the Debye temperature). The value of ΘD (= 46.3±0.9 K) so determined is in good agreement with that of Stevens and Stapleton from their T1, measurements in the range 1.5 to 7 K. In the Gd3+-doped glass, it was observed that (T1 -1) ∝ T over the range 50-150 K. The data for Ye3+-doped glass sample were accounted for by assuming that the phonon modulation of the ligand field is the dominant mechanism, associated with a low Debye temperature in accordance with the published data obtained by using other techniques to study lattice dynamics. On the other hand, the data on the Gd3+-doped glass sample were explained to be predominantly due to a mechanism involving Two-Level-Systems (TLS). © Springer-Verlag 1996 Printed in Austria