Search results for "Transit"
showing 10 items of 4210 documents
Effect of hydrogen on the ethylene polymerization process over Ziegler-Natta catalysts supported on MgCl2(THF)2. I. Studies of the chain-transfer rea…
2000
The effect of hydrogen on the molecular weight of polyethylene obtained over vanadium catalysts (based on VCl4 and VOCl3) supported on MgCl2(THF)2 was studied and the results were compared to those obtained for similar titanium catalysts. It was confirmed that the dependencies of the transfer reaction on the hydrogen concentration are a half-order in all investigated systems. However, the transition metal of the catalytic site affects the ratio of the transfer rate with hydrogen to the propagation rate (ktr,H/kp) and the results showed that hydrogen is a more effective agent of polyethylene molecular weight control in vanadium-based systems as compared to the titanium catalyst. © 2000 John …
X-ray Photoelectron-spectroscopy Investigation of Pumice-supported Nickel-catalysts
1995
Pumice-supported nickel catalysts, prepared by the method of slow homogeneous precipitation with urea, were analysed by x-ray photoelectron spectroscopy (XPS). By comparison with similarly prepared silica- and alumina-supported nickel catalysts, a preferential interaction of Ni2+ with Al3+ of the support has been determined. A quantitative XPS analysis indicated large segregation of nickel to the surface. The treatment with H2 at 673 K and 1073 K produced a partial reduction of Ni+2 to Ni0. The extent of the reduction was largest at 1073 K and in this case the reduced Ni in the metallic phase was detectable by x-ray diffraction. A decrease of the Ni 2p/Si 2p intensity ratio occurring in the…
Deep oxidation of propane using palladium–titania catalysts modified by niobium
2008
Abstract Pd/TiO 2 catalysts modified by niobium have been prepared and tested for the complete oxidation of propane. The catalysts have been characterised by BET, XRD, laser Raman spectroscopy, XPS, DRS and TPR. The incorporation of niobium into Pd/TiO 2 catalysts resulted in a marked increase in the catalytic activity compared to the Nb-free Pd/TiO 2 catalysts, and the activity increased as the niobium and/or palladium loading increased. The addition of Nb significantly modified the nature of the palladium and niobium species. There was a marked increase in the oxygen mobility after niobium addition. This could not only promote the presence of palladium species in a totally oxidized state …
Hydration dependence of myoglobin dynamics studied with elastic neutron scattering, differential scanning calorimetry and broadband dielectric spectr…
2014
In this work we present a thorough investigation of the hydration dependence of myoglobin dynamics. The study is performed on D2O-hydrated protein powders in the hydration range 0<h<0.5 (h≡gr[D2O]/gr[protein]) and in the temperature range 20-300K. The protein equilibrium fluctuations are investigated with Elastic Neutron Scattering using the spectrometer IN13 at ILL (Grenoble), while the relaxations of the protein + hydration water system are investigated with Broadband Dielectric Spectroscopy; finally, Differential Scanning Calorimetry is used to obtain a thermodynamic description of the system. The effect of increasing hydration is to speed up the relaxations of the myoglobin + hydration …
Pressure- and temperature-induced valence tautomeric interconversion in a o-dioxolene adduct of a cobalt-tetraazamacrocycle complex
2001
An electronic switch at the molecular level has been realized by using a class of ionic compounds of the formula [Co(L)(diox)]Y (L = tetraazamacrocyclic ligand, Y = mononegative anion). Such compounds undergo temperature- and pressure-induced intramolecular one-electron transfer equilibria. The transition temperature of interconversion varies with the nature of the counterions Y (Y = PF6, BPh4, I). Surprisingly the effect of the anion on the transition temperature is not only governed by its volume but also by its coulombic interaction.
From Single Molecules to Nanoscopically Structured Materials: Self-Assembly of Metal Chalcogenide/Metal Oxide Nanostructures Based on the Degree of P…
2011
A chemically specific and facile method for the immobilization of metal oxide nanoparticles onto the surface of IF-MoS2 nested fullerenes is reported. The modification strategy is based on the chalcophilic affinity of transition metals such as Fe2+/Fe3+, Fe3+, or Zn2+ as described by the Pearson HSAB concept. The binding capabilities of the 3d metals are dictated by their Pearson hardness. Pearson hard cations such as Fe3+ (Fe2O3) do not bind to the chalcogenide surfaces; borderline metals such as Fe2+ (Fe3O4) or Zn2+ (ZnO) bind reversibly. Pearson-soft metals like Au bind irreversibly. The immobilization of metal oxide nanoparticle colloids was monitored by transmission electron microscopy…
The CdCl2 effects on synthetic DNAs encaged in the nanodomains of a cationic water-in-oil microemulsion
2011
The present work is dedicated to the study of the interactions of CdCl(2) with the synthetic polynucleotides polyAT and polyGC confined in the nanoscopic aqueous compartment of the water-in-oil microemulsion CTAB/pentanol/hexane/water, with the goal to mimic in vitro the situation met by the nucleic acids in vivo. In biological structures, in fact, very long strings of nucleic acids are segregated into very small compartments having a radius exceedingly smaller than the length of the encapsulated macromolecule. For comparison, the behaviour of polyGC was also studied in aqueous solutions of matched composition. The conformational and thermal stabilities of both polynucleotides enclosed in t…
Les formations professionnelles de l'enseignement supérieur en France au prisme de l'insertion et de la mobilité sociale des diplômés
2014
La professionnalisation des formations dans l'enseignement supérieur en France s'est développée ces dernières décennies avec pour objectif d'améliorer l'employabilité des jeunes diplômés dans un contexte de dégradation de leurs conditions d'insertion. À partir des trois dernières enquêtes Génération du Céreq, ce travail questionne la performance de ces filières professionnelles par rapport aux filières plus académiques de l'enseignement supérieur, en période de crise économique. Certaines formations, comme par exemple les licences professionnelles, garantissent toujours de bonnes conditions d'insertion, pour autant les effets concernant la mobilité sociale en début de carrière, sont plus nu…
Geoterminen energia ja politiikkaongelmien hallitsemisen tiedollinen haaste
2022
Ilmastonmuutoksen hillitsemiseksi energiajärjestelmän on muututtava vähähiilisemmäksi. Geoterminen energia on Suomessa ja muualla maailmassa noussut yhdeksi päästöttömäksi uusiutuvan energian muodoksi, mutta sen rakentamiseen ja käyttöön sisältyy riskejä. Tässä artikkelissa tarkastelemme geotermisen energian seismisen riskin hallintaa monitoimijaisessa verkostossa. Keskitymme siihen, millaisena eri toimijat näkevät Seismologian instituutin aseman geotermisen energian hallinnan verkostossa. Pohdimme, miten geotermisen energian seismisen riskin hallinnan kaltainen kompleksinen politiikkaongelma jäsentyy institutionaalisesti epäselvässä tilanteessa ja millaisia tietoon ja tietämiseen liittyviä…
Observatoire de la Transition Socioécologique en Bourgogne Franche-Comté : Méthodes et résultats
2022
Présentation de la méthode et des résultats quantitatif et qualitatifs 2022 de l'étude de l'Observatoire de la Transition Socioécologique en Bourgogne Franche-Comté.