Search results for "atran"

Interaktiivisen tietokantasovelluksen toteutus WebSpeedillä

2000

Molecular precursors of mesostructured silica materials in the atrane route: A DFT/GIAO/NBO theoretical study

2007

Abstract Quantum chemical calculations using density functional theory have been carried out to investigate two assumed molecular precursors and identified as silatranes (N[OCH2CH2]3Si–OCH2CH2N–(CH2CH2OH)2 and N[OCH2CH2]3Si–OCH2CH2N–(CH2CH2OH)2Na+) which are present in the synthesis of mesoporous silica based material namely “the atrane route”. One of the ways in this synthesis leads to the well-known MCM-41. Additionally, in this work has been also investigated two others molecules such as triethanolamine (TEAH3) and sodatrane which are present in the medium. Gas phase and solution equilibrium geometries of the previous molecules were fully optimized at B3LYP level, modeling solvent effect…

Nanoparticulated Silicas with Bimodal Porosity: Chemical Control of the Pore Sizes

2008

Nanoparticulated bimodal porous silicas (NBSs) with pore systems structured at two length scales (meso- and large-meso-/macropores) have been prepared through a one-pot surfactant-assisted procedure by using a simple template agent and starting from silicon atrane complexes as hydrolytic inorganic precursors. The final bulk materials are constructed by an aggregation of pseudospherical mesoporous primary nanoparticles process, over the course of which the interparticle (textural) large pore system is generated. A fine-tuning of the procedural variables allows not only an adjustment of the processes of nucleation and growth of the primary nanoparticles but also a modulation of their subseque…

Influence du court noué sur la diversité fonctionnelle des champignons mycorhiziens à arbuscules dans des racines et du sol de vigne

2022

Le court-noué (CN) correspond à un dépérissement infectieux (népovirus) qui apparaît par taches au sein des parcelles. Cette maladie entraîne une dégénérescence progressive de la vigne qui conduit in fine à la mort des ceps. A l’heure actuelle, environ 60% du vignoble national serait touché, dont 30% de façon importante. Seize népovirus sont responsables de dégénérescence ou de dépérissement de la vigne. Cependant, le Grapevine FanLeaf Virus (GFLV) est le principal agent responsable. Il est transmis spécifiquement de plante à plante par un nématode ectoparasite du sol, Xiphinema index. Les nématodes, en piquant successivement deux ceps voisins dont les racines sont proches, inoculent le vir…

Alternative to oral dicoumarin anticoagulants: Considerations in dental care

2013

Introduction: For over 50 years, vitamin K antagonists such as warfarin (Aldocumar®) and acenocoumarol (Sintrom®) have been the gold standard for reducing the risk of cerebrovascular events. In the last 5 years alternative anticoagulants have been evaluated that act directly upon a concrete target within the coagulation cascade, thereby affording a more predictable anticoagulant effect. The present study offers an update on the new oral anticoagulants and reviews the implications referred to the dental care of patients administered these substances. Material and methods: An exhaustive PubMed-Medline and Cochrane Library search was made of the main alternatives to conventional oral anticoagu…

Influence of a nonlinear coupling on the supratransmission effect in modified sine-Gordon and Klein–Gordon lattices

2017

International audience; In this paper, we analyze the conditions leading to the nonlinear supratransmission phenomenon in two different models: a modified fifth order Klein–Gordon system and a modified sine-Gordon system. The modified models considered here are those with mixed coupling, the pure linear coupling being associated with a nonlinear coupling. Especially, we numerically quantify the influence of the nonlinear coupling coefficient on the threshold amplitude which triggers the nonlinear supratransmission phenomenon. Our main result shows that, in both models, when the nonlinear coupling coefficient increases, the threshold amplitude triggering the nonlinear supratransmission pheno…

New heterogeneous catalysts for greener routes in the synthesis of fine chemicals

2007

Abstract New strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated to previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Following these procedures, catalysts with different Si/Sn ratios—21.8 to 50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7—were prepared. These new materials were tested in the acylation of aromatic sulfonamides using…

Selective oxidative activation of isobutane on a novel vanadium-substituted bimodal mesoporous oxide V-UVM-7

2006

Abstract New vanado-silicates with a bimodal mesoporous system (V-UVM-7) and high vanadium contents (Si/V ≥ 7) have been prepared by a modification of the so-called atrane method. Its morphology consists of aggregation of nano-particles with V-MCM-41 structure, creating a second broader porous system in their interparticle space. Its structure allows to incorporate a high V contents into tetrahedral sites of the framework while keeping vanadium dispersion. V-UVM-7 catalysts are very active and selective for the direct transformation of isobutane to isobutene and methacrolein. Total conversion and methacrolein-to-isobutene ratio in the products increased with increasing vanadium contents. Th…

Efficient Sc triflate mesoporous-based catalysts for the synthesis of 4,4′-methylenedianiline from aniline and 4-aminobenzylalcohol

2012

Abstract Sc triflate mesoporous-based catalysts have been prepared using a two-step strategy (i.e., Atrane method) based on the formation of the hierarchic bimodal porosity in the first step and the formation of Sc triflate complexes at the materials surface in the second step. All solids were analyzed by EPMA, surface area, and pore size values, XRD, TEM, FTIR, and 45Sc NMR static spectra. The catalysts have been investigated in the synthesis of 4,4′-methylenedianiline (4,4′-MDA) from aniline and 4-aminobenzylalcohol. 4,4′-MDA was obtained with selectivities over 85.0% for a conversion of aniline of 31%, at 80 °C and after 24 h. Using microwaves, selectivities of 90% in 4,4′-MDA were reach…

Analysis of nonlinear coupling on the behavior of the sine-Gordon and Klein-Gordon models in bandwidth and forbidden bands

2017

In this thesis, we analyze the conditions of existence of the phenomenon of nonlinear supratransmission in two different models: a modified fifth-order Klein-Gordon system and a modified sine-Gordon system. The modified models considered here are those with mixed coupling, the pure linear coupling being associated with a nonlinear coupling. In particular, we quantify numerically the influence of the non-linear coupling coefficient on the threshold amplitude which triggers the phenomenon of non-linear supratransmission. Our main result shows that in both models, when the nonlinear coupling coefficient increases, the threshold amplitude triggering the phenomenon of nonlinear supratransmission…