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771.
Amziane A Amari M Mounier D Breteau JM Joly N Banchet J Tisseur D Gusev V 《Ultrasonics》2012,52(1):39-46
Laser ultrasonics was applied to the manufacturing control of the integrity (no failure) of coated spherical particles designed for High Temperature Reactors (HTR). This control is of major importance, since the coating of the nuclear fuel kernel is designed to prevent from the diffusion of fission products outside the particle during reactor operation. The SiC layer composing the coating is particularly important, since this layer must be an impenetrable barrier for fission products. The integrity of the SiC shell (no crack within the shell) can be assessed by the ultrasonic vibration spectrum of the HTR particle, which is significantly changed, compared to the reference spectrum of a defect-free particle. Spheroidal vibration modes of defect-free dummy particles with a zirconium dioxide (ZrO2) core were observed in the 2-5 MHz range. A theoretical analysis is presented to account for the observed vibration spectra of defect-free or cracked HTR particles. 相似文献
772.
Area preserving diffeomorphisms of the 2-disk which are Identity near the boundary form a group which can be equipped, using theL
2-norm on its Lie algebra, with a right invariant metric. In this paper we give a lower bound on the distance between diffeomorphisms which is invariant under area preserving changes of coordinates and which improves the lower bound induced by the Calabi invariant. In the case of renormalizable and infinitely renormalizable maps, our estimate can be improved and computed. 相似文献
773.
Marie-Elodie Godard Jean-Marc Saiter Pilar Corts Salvador Montserrat John M. Hutchinson Fabrice Burel Claude Bunel 《Journal of Polymer Science.Polymer Physics》1998,36(4):583-593
In this work, we have investigated by DSC the structural relaxation of amorphous polymethyl(α-n-alkyl)acrylates in which it is possible to change the length of the alkyl chain. We have evaluated the Narayanaswamy parameter, x, which controls the relative contribution of temperature and of structure to the relaxation time, the apparent activation energy, Δh*, and the nonexponentiality parameter, β, of the stretched exponential response function. The results suggest that x increases while Δh* decreases and β remains constant as the length of the side chain increases. This allows us to comment on the effect of chemical modification on the relaxation kinetics. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 583–593, 1998 相似文献
774.
Kinani S Bouchonnet S Bourcier S Porcher JM Aït-Aïssa S 《Journal of chromatography. A》2008,1190(1-2):307-315
This study compares different silylation procedures of zearalenone and its metabolites: alpha-zearalenol, beta-zearalenol, zearalanone, alpha-zearalanol and beta-zearalanol for gas chromatography-mass spectrometry (GC-MS) analysis. Four silylating agents among the most frequently used to derivatize polar organic compounds were tested: N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), N,N-diethyltrimethylsilylamine (TMSDEA) and a commercial mixture of N,O-bis(trimethylsilyl)acetamide, trimethylchlorosilane and N-trimethylsilyimidazole. Previous studies showed that the addition of polar and/or basic solvents can significantly improve the yield of a reaction of derivatization. In this work, four solvents were tested: pyridine, dimethylformamide, acetonitrile and acetone. The influence of each solvent was studied as a function of the silylating agent/solvent ratio. The influences of the temperature and of the reaction time on the reaction yields were also evaluated. A GC-MS quantitation method associating methanol chemical ionization and selected ion storage with three ions was developed and successfully tested on a reconstituted sediment spiked in zearalenone and its metabolites. 相似文献
775.
Orientation of mica and talc platelets in injection-molded polyamide 6.6 was investigated by X-ray diffraction (diffractometry, pole figures). The platelets are nearly perpendicular to the plane of the molded plaque in the core, and parallel to it in the skin. These orientations are related to the shear and elongation rate distribution in the thickness of the molding. 相似文献
776.
Louis Godeffroy Dr. Paolo Ciocci Dr. Nathaly Ortiz Peña Dr. Damien Alloyeau Dr. Jean-Marc Noël Dr. Jean-François Lemineur Dr. Frédéric Kanoufi 《Angewandte Chemie (International ed. in English)》2023,62(29):e202304950
This work proposes a novel method for measuring the intrinsic activity of single metal-based nanoparticles towards water reduction in neutral media at industrially relevant current densities. Instead of using gas nanobubbles as proxy, the method uses optical microscopy to track the local footprint of the reaction through the precipitation of metal hydroxide, which is associated to the local pH increase during electrocatalysis. The results show the electrocatalytic activities of different types of metal nanoparticles and bifunctionnal core-shell nanostructures made of Ni and Pt, and demonstrate the importance of metal hydroxide nano-shells in enhancing electrocatalysis. This method should be generalizable to any electrocatalytic reaction involving pH changes such as nitrate or CO2 reduction. 相似文献
777.
Interpenetrating polymer systems based on crosslinked polyurethane (PU) and polystyrene (PS) were prepared at room temperature by a one-shot (in situ) method, starting from an initial homogeneous mixture of reagents via non interfering mechanisms. Both polymerizations were performed either simultaneously or one after the other. Crosslinks and/or covalent bonds between components were deliberately introduced by the addition of appropriate monomers, in order to tailor the degree of microphase separation. Depending on the formation process, transluscent or transparent films were obtained, despite the difference in refractive index of the components. The maximum of miscibility, taken as from the glass transition criterion, was obtained for sequential tightly graft interpenetrating networks. 相似文献
778.
Catherine Grandin Elie About-Jaudet Noël Collignon Jean-Marc Denis Philippe Savignac 《Heteroatom Chemistry》1992,3(4):337-343
Diisopropyl 1,1-dichloroalkylphosphonates bearing various groups (alkyl, aryl, allyl, benzyl, phenylthiolate, trimethylsilyl) in the α-position were reduced to the corresponding primary 1,1-dichlorophosphines by the LiAlH4-AlCl3 system in diethyl ether. Subsequent dehydrochlorination with tertiary amines in the presence of trapping dipolar compounds (ethyl diazoacetate or n-hexylazide) led to the expected 1,2,4-diazaphospholes or 3H-1,2,3,4-triazaphospholes. 相似文献
779.
A series of polyampholytes of sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS) and 2-(methacryloyloxy)ethyltrimethylammonium chloride (MADQUAT) has been synthesized by polymerization in microemulsions. The reaction products are stable inverse latexes consisting of high molecular weight copolymers entrapped in water droplets of small size (d % 80 nm) and dispersed in an isoparaffinic oil. The optimization of the formulation was by a selection procedure based on the hydrophile-lipophile balance of the emulsifiers and solubility parameters of the different components. Both ionomers play an important role in the formulation owing to their amphiphilic and electrolyte characters. Reactivity parameter studies yield rA and rM values of 0.81 and 1.97 for NaAMPS and MADQUAT, respectively. The properties of polyampholytes in pure water and in salt solutions were investigated by turbidimetry and viscometry experiments. The results are compared with the recently developed theory of Higgs and Joanny (J. Chem. Phys. 94, 1543 (1991)). 相似文献