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61.
62.
Francois Delyon Yves Lévy Bernard Souillard 《Communications in Mathematical Physics》1985,100(4):463-470
We prove that discrete Schrödinger operators on
d
with a random-potential have almost-surely only pure point spectrum and exponentially decaying eigenfunctions for large disorder or large energy. This is the first proof of localization for multi-dimensional Anderson models.Groupe de recherche 048 du CNRS 相似文献
63.
Koteswara Rao Y Vijaya Bhaskar Reddy M Venkata Rao C Gunasekar D Blond A Caux C Bodo B 《Chemical & pharmaceutical bulletin》2002,50(9):1271-1272
Two new 5-deoxyflavones, 7,8-dimethoxy-3',4'-methylenedioxyflavone (1) and 7,2',4'-trimethoxyflavone (2) together with a known flavone, 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the rootbark of Albizia odoratissima. The structures of these new compounds were elucidated by electrospray ionization mass spectrometry (ESI-MS) and 1D and 2D-NMR spectral studies including (1)H-(1)H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY). 相似文献
64.
[reaction: see text] A recently discovered multicomponent coupling reaction is used to give direct access to a late intermediate in the synthesis of frondosin B. This intermediate can also be efficiently converted to a ring-expanded analogue of frondosin B by sustained heating of the reaction mixture. An unprecedented tandem 1,7-hydrogen shift, 8pi-electrocyclization is proposed to explain the formation of this ring-expanded species. 相似文献
65.
1,3,5-Trisubstituted hexahy drotriazines react with hydrogen chloride in the presence of anhydrous solvents to form useful intermediates for the introduction of the RNHCH2- group into compounds which undergo the Mannich reaction. The effectiveness of the new aminomethyl-ating agent has been demonstrated by the preparation of secondary aminomethyl sulfide hydro-chlorides. 相似文献
66.
Céline Pascal Claude Merlet Rose-Marie Marin-Ayral Jean-Claude Tedenac Bernard Boyer 《Mikrochimica acta》2004,145(1-4):147-151
The phases formed at the interface between an intermetallic (NiAl) and a nickel base superalloy joined by combustion synthesis were investigated, particularly the eutectic phases. Owing to their small size, the characterisation of these phases using a Castaings electron microprobe encounters difficulties. The analysis volume size is generally too large to differentiate the phases from their surrounding matrix, even by using low accelerating voltage. Moreover, the eutectic phases contain boron, which is difficult to characterise by EPMA. Independently of the phases shape, the characterisation can be solved by viewing this complex system as a surrounding matrix and a multi layer system. The results of these simulations revealed the presence of two categories of borides: the eutectic boride MM2B2 (M=Mo and M=Co, Cr) and the solid solution boride [Cr1–x (Mo, W)x]B. 相似文献
67.
Inverse gas chromatography using water probing at 110°C was carried out to characterize rayon yarns after prior heating at 200 and 250°C in both inert (nitrogen) and oxidative (dry air) atmospheres for successively longer time intervals. During the early stages of heating in either atmosphere, the affinity of the rayon for water drops rapidly. However, whereas continued heating in N2 results in a further loss of activity, data have been obtained showing that after an initial period yarns heated in air at 250°C exhibit an increasing attraction for water even while losing more weight. 相似文献
68.
Messaoud T Duplâtre G Waton G Michels B 《Physical chemistry chemical physics : PCCP》2005,7(22):3839-3844
The new method based on positron annihilation lifetime spectroscopy (PALS) to determine both the mean core radius, R(core), and aggregation number, N(ag), of micelles is applied to the study of aqueous solutions of the triblock Pluronic P84 copolymer as a function of temperature (T), beyond the gelification point (334 K). Two long-lived components appear in the PALS spectra, ascribed to triplet positronium in the water bulk (o-Ps(aq)) and in the organic core of the micelles (o-Ps(org)). Of the various fitting parameters, only the lifetime of the latter species, tau4, and the micellar parameters, R(core) and N(ag), disclose the occurrence of gelification by first increasing up to 334 K, then decreasing. By contrast to what is known in case of phase transition, none of the parameters shows any abrupt change at 334 K, whereas the macroscopic viscosity of the solutions suffers a drastic increase. This is attributed to the fact that positronium is sensitive to the microviscosity of the solutions. At the transition point, the properties of the polyoxipropylene aggregates forming the organic core of the P84 micelles are not greatly affected. Furthermore, the fact that the experimental N(ag) values coincide with those calculated for spheres, from the R(core) values, indicates that the shape of the P84 cores does not change significantly after gelification. The onset of gelification results from a decrease in the hydrogen bonding interactions in the solution with an ensuing relative increase in the interactions between the polyoxipropylene (PPO) groups, initially forming the corona of the P84 micelles, in an intermicellar mode. This increased solicitation of the PPO groups outside their initial location would result in depletion in the number of surfactant molecules forming the micelles, viz. a decrease in both R(core) and N(ag) above 334 K. From the data, additional information can be gained regarding the local viscosity and surface tension in the micellar cores. 相似文献
69.
Maria Teresa Cocco Cenzo Congiu Valentina Onnis Angela Maria Bernard Pier Paolo Piras 《Journal of heterocyclic chemistry》1997,34(4):1347-1350
A simple approach to the fluorinated 1,5-benzoxazepine ring system is described. By reacting commercially accessible aminophenols 1 and the trifluoroacetylvinyl ether 2, high yields of enaminones 3 were obtained. Functionalization of methyl group of compounds 3 gave rise to dieneamines 4 that were cyclized in acidic environment to benzoxazepine derivatives 5. 相似文献
70.
Fuminori Goda Bernard Gallez Harold M. Swartz 《Research on Chemical Intermediates》1996,22(5):491-498
PCA (2,2,5,5-tetramethylpiperidine-1-oxyl-3-carboxylic acid) is a relatively stable free radical which has been shown to be useful as a contrast agent for nuclear magnetic resonance imaging and as an imaging/spectroscopy agent for EPR. In an effort to determine the role of the liver and kidney in the pharmacokinetics of PCA, using low frequency in vivo EPR spectroscopy, we followed the clearance of PCA after intravenous injection in mice: under normal conditions, with a restricted blood supply to the kidneys, after exposure to an acute hepatotoxin CCl4, and after exposure to lipopolysaccharide (endotoxin). The observed pharmacokinetics fit a two-component model. The fast component was dramatically affected when the renal vessels were restricted, while CCl4 and endotoxin had a smaller but significant effect. The half times of the slow components were not significantly different (p>0.05) in the groups treated by renal blood flow occlusion, CCl4, or LPS, compared with the control group. In conclusion, we find that the pharmacokinetics of PCA need to be completely described in term of a two component model: the fast component of the decay is mainly due to the elimination by the kidneys and also is affected by the time for the initial distribution; the slow component is related to the bioreduction of the nitroxide. In addition to the liver other tissues can also effectively metabolize PCA. The effect of oxygen on the rate of metabolism is modest at most. 相似文献