Thermal Conductivity of Ordered Mesoporous Nanocrystalline Silicon Thin Films Made from Magnesium Reduction of Polymer-Templated Silica

This paper reports the cross-plane thermal conductivity of ordered mesoporous nanocrystalline silicon thin films between 25 and 315 K. The films were produced by evaporation induced self-assembly of mesoporous silica followed by magnesium reduction. The periodic ordering of pores in mesoporous silicon was characterized by X-ray diffraction and direct SEM imaging. The average crystallite size, porosity, and film thickness were about 13 nm, 25-35%, and 140-340 nm, respectively. The pores were arranged in a face-centered cubic lattice. The cross-plane thermal conductivity of the mesoporous silicon thin films was measured using the 3ω method. It was between 3 and 5 orders of magnitude smaller than that of bulk single crystal silicon in the temperature range considered. The effects of temperature, film thickness, and copolymer template on the thermal conductivity were investigated. A model based on kinetic theory was used to accurately predict the measured thermal conductivity for all temperatures. On the one hand, both the measured thermal conductivity and the model predictions showed a temperature dependence of k proportional to T2 at low temperatures, typical of amorphous and strongly disordered materials. On the other hand, at high temperatures the thermal conductivity of mesoporous silicon films reached a maximum, indicating a crystalline-like behavior. These results will be useful in designing mesoporous silicon with desired thermal conductivity by tuning its morphology for various applications

Thermal conductivity of cubic and hexagonal mesoporous silica thin films

This paper reports the cross-plane thermal conductivity of highly ordered cubic and hexagonal templated mesoporous amorphous silica thin films synthesized by evaporation-induced self-assembly process. Cubic and hexagonal films featured spherical and cylindrical pores and average porosities of 25% and 45%, respectively. The pore diameters ranged from 3 to 18 nm and film thickness from 80 to 540 nm, while the average wall thickness varied from 3 to 12 nm. The thermal conductivity was measured at room temperature using the 3 omega method. The experimental setup and the associated analysis were validated by comparing the thermal conductivity measurements with the data reported in literature for the silicon substrate and for high quality thermal oxide thin films with thicknesses ranging from 100 to 500 nm. The cross-plane thermal conductivity of the synthesized mesoporous silica thin films does not show strong dependence on pore size, wall thickness, or film thickness. This is due to the fact that heat is mainly carried by very localized nonpropagating vibrational modes. The average thermal conductivity for the cubic mesoporous silica films was 0.30 +/- 0.02 W/m K, while it was 0.20 +/- 0.01 W/m K for the hexagonal films. This corresponds to reductions of 79% and 86% from bulk fused silica at room temperature

Mise en réseau d’expérimentations de longue durée de systèmes de grande culture en agriculture biologique : apports méthodologiques et enseignements pour des systèmes très économes en phytosanitaires

Le Réseau RotAB regroupe 12 dispositifs expérimentaux systémiques de longue durée, ayant en commun l’objectif d’étudier la durabilité de systèmes de grande culture innovants en Agriculture Biologique (AB). Tous reposent sur la mobilisation forte de leviers agroécologiques pour maintenir voire développer la fertilité des sols et contrôler le développement de la flore adventice, sans utiliser de produits phytosanitaires. Le travail en réseau permet de traiter collectivement les questions posées. Elles portent sur (i) la conception de systèmes agroécologiques en grande culture en AB, (ii) la conception des dispositifs et moyens nécessaires pour les évaluer dans leur ensemble et dans la durée, (iii) la capitalisation des données et leur valorisation. Les activités menées reposent sur une démarche de partage entre les membres du réseau et d'amélioration des approches face à des questions spécifiques, en mobilisant l'intelligence collective. Après 6 années de fonctionnement, le réseau tire un bilan positif des travaux menés en commun. Ils ont majoritairement concerné des apports méthodologiques. Les perspectives sont aujourd’hui de travailler sur l’amélioration de la valorisation de résultats et la communication vers des agriculteurs en réduction d’intrants, en particulier d’herbicides. Des perspectives sont aussi ouvertes par le lancement d’un réseau européen d’expérimentations de longue durée en ABThe “RotAB network” consists of 12 long term systemic experiments, having in common the objective of studying the sustainability of innovative arable cropping systems in organic farming (OF). All rely on the strong mobilization of agroecological levers, to maintain or develop soil fertility and to control weeds, without using phytosanitary products. Networking makes it possible to deal collectively with the questions each one has to deal with. They concern (i) the design of agroecological systems in arable cropping systems in OF, (ii) the design of the devices and means necessary to evaluate them as a whole and in the long term, (iii) the data capitalization and their valuation. The activities carried out are based on a sharing process between network members and improvement of approaches to specific issues, mobilizing collective intelligence. After 6 years, the network draws a positive assessment of the work carried out jointly. It mainly concerns methodological contributions. The prospects are today to work on improving the capitalization of results and communication to farmers for reducing inputs, especially herbicides. The launch of a European network of long-term experiments in AB is another main issue for next year

Specificity of cGMP binding to a purified cGMP-stimulated phosphodiesterase from bovine adrenal tissue.

The binding of [3H]cGMP (guanosine 3',5'-monophosphate) to purified bovine adrenal cGMP-stimulated phosphodiesterase was measured by Millipore filtration on cellulose ester filter. [3H]cGMP-binding activity was enhanced when the assay was terminated in buffer containing 70% of saturated ammonium sulfate to dilute the enzyme and wash the filters. The cGMP-binding activity was co-purified with the phosphodiesterase activity. The binding of [3H]cGMP to purified enzyme was measured in the presence or absence of the phosphodiesterase inhibitor, 1-methyl-3-isobutylxanthine. 1-Methyl-3-isobutylxanthine showed linear competitive inhibition with respect to cGMP as substrate in the phosphodiesterase reaction but stimulated the [3H]cGMP-binding activity in the binding assay. The stimulatory effect appeared not to be the result of preservation from [3H]cGMP hydrolysis; no cGMP phosphodiesterase activity has been measured under the cGMP-binding assay conditions, in the absence or presence of the inhibitor. Half-maximal stimulation by 1-methyl-3-isobutylxanthine occurred in the 5-7 microM concentration range. The specificity of binding of [3H]cGMP was investigated by adding increasing concentration of unlabeled analogs of cAMP (adenosine 3',5'-monophosphate) and cGMP. The binding of [3H]cGMP (50 nM) was displaced by unlabeled cGMP and cAMP with the following potency: 50% displacement was reached at the 0.1 microM cGMP range and only at a fiftyfold higher cAMP concentration. Our data with comparative series of analogs (e.g. 5'-amino-5'-deoxyguanosine 3',5'-monophosphate and 3'-amino-3'-deoxyguanosine 3',5'-monophosphate) showed that the potencies of stimulation of cAMP phosphodiesterase activity parallels displacement curves or [3H]cGMP binding to purified enzyme with no correlation with phosphodiesterase inhibition sequences. Those experiments suggest that the cGMP-binding activity is directly related to the non-catalytic (allosteric) cGMP-binding site.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe