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11.
Let be an elliptic curve with complex multiplication, defined over . We consider linear forms on with coefficients in the CM field of . Within this framework, we present a new measure of linear independence for elliptic logarithms in (logb)(loga)n. Like recent advances in this domain (works by Ably, David, Hirata-Kohno), our result is best possible in terms of the height of the linear forms (logb) while providing a better estimate in the height of algebraic points considered (loga), removing a term in logloga. To cite this article: M. Ably, É. Gaudron, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
12.
Most adhesives and binders, including bitumen for asphalt mixture production, are presently produced from petrochemicals after
the refining of crude oil. The fact that crude oil reserves are a finite resource means that in the future, it may become
necessary to produce these materials from alternative and probably renewable sources. Suitable resources of this kind may
include polysaccharides, plant oils and proteins. This paper deals with the synthesis of polymer binders from monomers that
could, in future, be derived from renewable resources. These binders consist of polyethyl acrylate (PEA) of different molecular
weight, polymethyl acrylate (PMA) and polybutyl acrylate (PBA), which were synthesised from ethyl acrylate, methyl acrylate
and butyl acrylate, respectively, by atom transfer radical polymerisation. The rheological properties of these binders were
determined by means of oscillatory testing using a dynamic shear rheometer and combinations of stress/strain, temperature
and frequency sweeps. The results indicate that PEA can be produced to have rheological properties similar to that of ‘soft’
100/150 penetration grade bitumen, PMA with similar rheological properties to that of ‘hard’ 10/20 penetration grade bitumen,
while PBA, due to its highly viscous nature and low dynamic moduli, cannot be used on its own as a binder. The synthetic polymers
were found to be thermo-rheologically simple, and the shift factors, used to produce the dynamic moduli master curves, were
found to fit an Arrhenius function. 相似文献
13.
Mohamed Haouas Amine Harrane Mohamed Belbachir Francis Taulelle 《Journal of Polymer Science.Polymer Physics》2007,45(22):3060-3068
Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. 1H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. 27Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the 29Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007 相似文献
14.
A variety of aromatic amines are oxidized to their corresponding quinones in excellent yields by supported iodic acid under microwave irradiation and solvent free conditions. 相似文献
15.
Although pentamethylene sulfide (tetrahydrothiopyran) lacks acidic hydrogen, OsVIII has been found to catalyze its oxidation by alkaline K3Fe(CN)6 to produce 3-hydroxypentamethylene sulfide as the only product. The kinetics reveal first-order dependence on ferricyanide and OsVIII, and zero order on pentamethylene sulfide and OH–. The effects of introduced electrolytes, K4Fe(CN)6, relative permittivity and temperature have also been studied. On the basis of kinetic evidence, a mechanism that involves anation of the osmium catalyst (sulfide/water interchange) followed by intramolecular proton abstraction, followed by an electron transfer step has been proposed and discussed. 相似文献
16.
The aim of this paper is to present two different approachs in order to obtain an existence result to the so-called quadrature
surface free boundary problem. The first one requires the shape derivative calculus while the second one depends strongly
on the compatibility condition of the Neumann problem. A necessary and sufficient condition of existences is given in the
radial case. 相似文献
17.
Heterometallic molecular chromium wheels are fascinating new magnetic materials. We reexamine the available experimental susceptibility data on MCr7 wheels in terms of a simple isotropic Heisenberg Hamiltonian for M=Fe, Ni, Cu, and Zn and find in that FeCr7 needs to be described with an iron–chromium exchange that is different from all other cases. In a second step we model the behavior of the proton spin lattice relaxation rate as a function of applied magnetic field for low temperatures as it is measured in nuclear magnetic resonance (NMR) experiments. It appears that CuCr7 and NiCr7 show an unexpectedly reduced relaxation rate at certain level crossings. 相似文献
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20.
Wadie Tadros Alfy Badie Sakla Sami Bassili Awad Abdul-Aziz Amine Helmy 《Helvetica chimica acta》1972,55(8):2808-2812
1, 2-Di-(p-methoxyphenyl)-ethane-1, 2-diol gave in acid media bis-(4-methoxy-phenyl)-acetaldehyde, 4-4′-dimethoxy-deoxybenzoin, and 1, 2-di-(p-methoxyphenyl)-ethylene oxide; their respective yields being influenced by at least 3 factors: (i) the acid, (ii) its concentration, and (iii) the reaction period. Bis-(4-methoxyphenyl)-acetaldehyde rearranged to the deoxybenzoin in boiling sulfuric (50%) or phosphoric (75%) acids (w/w), and to two isomeric 1, 2-diacetoxy-1, 2-di-(p-methoxyphenyl) ethanes when it was heated with acetic anhydride. The mechanisms of these reactions are discussed. 相似文献