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161.
Amy F Enriquez H Soukiassian P Storino PF Chabal YJ Mayne AJ Dujardin G Hwu YK Brylinski C 《Physical review letters》2001,86(19):4342-4345
The atomic scale oxidation of the alpha-SiC(0001)-(3 x 3) surface is investigated by atom-resolved scanning tunneling microscopy, core level synchrotron radiation based photoemission spectroscopy, and infrared absorption spectroscopy. The results reveal that the initial oxidation takes place through the relaxation of lower layers, away from the surface dangling bond, in sharp contrast to silicon oxidation. 相似文献
162.
Richeter S Jeandon C Gisselbrecht JP Graff R Ruppert R Callot HJ 《Inorganic chemistry》2004,43(1):251-263
This article describes the preparation of several new porphyrins bearing chelating peripheral groups fully conjugated with the macrocyclic pi-system. Treatment of a 2-nitro-meso-tetraarylporphyrin with phosphite gave a cyclic enamine, whose formylation gave an enaminoaldehyde. The thio analogue was obtained on treatment with Lawesson's reagent. The same reagent was also used to obtain the isomeric thioenaminoketone chelates. A enaminoketone ligand was prepared from a porphyrinic pyrrolone. All these ligands, as internal nickel complexes, could be metalated with palladium to yield porphyrinic dimers. The dimers obtained from enaminoketones and thioketones show a trans geometry, while in the enaminoaldehyde and -thioaldehyde series the cis isomer is thermodynamically favored. The bathochromic shifts of the electronic spectra of the aldehyde-derived dimers illustrate the strong electronic effect of peripheral metalation and dimerization. However, in the case of the pyrrolone-derived ligand, opposite effects were observed, due to partial reconstitution of the porphyrin chromophore on complexation. As with the dimers derived from enaminoketones, the dimers derived from the new ligands show typical splitting (up to 190 mV) of the electrochemical waves confirming large porphyrin-porphyrin interactions. 相似文献
163.
Seven upper-rim fully tethered cyclodextrins (URFT-CDs) have been synthesised in a good average coupling yield using the one-step "phosphine imide" approach and their metal complexation behaviour with lanthanides and transition metals was explored. We observed that the A-TE-E light conversion process (antennae effect) occurs in the URFT-CD lanthanide complexes. A molecular redox switch based on the corresponding iron complexes is also reported. A reversible intramolecular translocation of the FeII and FeIII ions, between two distinct binding cavities has been monitored spectroscopically and achieved by chemical triggering. Finally, a negative allosteric control of ion recognition through the formation of a CD pseudocryptand is discussed. 相似文献
164.
John-Paul Latham Antonio Munjiza Julian Mindel Jiansheng Xiang Romain Guises Xavier Garcia Chris Pain Gerard Gorman Matthew Piggott 《Particuology》2008,6(6):572-583
The seaward slope of many breakwaters consists of thousands of interlocking units of rock or concrete comprising a massive granular system of large elements each weighing tens of tonnes. The dumped quarry materials in the core are protected by progressively coarser particulates. The outer armour layer of freely placed units is intended to both dissipate wave energy and remain structurally stable as strong flows are drawn in and out of the particulate core. Design guidance on the mass and shape of these units is based on empirical equations derived from scaled physical model tests. The main failure mode for armour layers exposed to severe storms is hydraulic instability where the armour units of concrete or rock are subjected to uplift and drag forces which can in turn lead to rocking, displacement and collisions sufficient to cause breakage of units. Recently invented armour unit designs making up such granular layered system owe much of their success to the desirable emergent properties of interlock and porosity and how these combine with individual unit structural strength and inertial mass. Fundamental understanding of the forces governing such wave-structure interaction remains poor. We use discrete element and combined finite-discrete element methods to model the granular solid skeleton of randomly packed units coupled to a CFD code which resolves the wave dynamics through an interface tracking technique. The CFD code exploits several methods including a compressive advection scheme, node movement, and general mesh optimization. We provide the engineering context and report progress towards the numerical modelling of instability in these massive granular systems. 相似文献
165.
Laser‐induced breakdown spectroscopy (LIBS) and Raman microscopy were used for the identification of pigments in wall painting. Raman spectroscopy, which provides the molecular ‘fingerprint’ of the compound, is nowadays widely used by the archaeometry community, especially for pigment analysis. LIBS, which provides the elementary composition of samples, is a rapid noncontact method, enabling layer‐by‐layer analysis through a precise laser ablation of the sample. This work deals with the behavior of pigments after a LIBS analysis, by trying to identify the compounds before and after the laser shot. Six commercial pigments prepared with the fresco technique were investigated: ultramarine blue, red lead, charcoal, a yellow and a red ochre, and a green earth. Raman spectra, acquired on the sample surface and in the crater induced by LIBS analysis, were compared. The results show that these pigments are well recognized after a LIBS measurement. The analysis of green earth illustrates that the combination of these two techniques gives complete information from a sample. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
166.
Bejoy Thomas Niki Baccile Sylvie Masse Caroline Rondel Isabelle Alric Romain Valentin Zéphirin Mouloungui Florence Babonneau Thibaud Coradin 《Journal of Sol-Gel Science and Technology》2011,58(1):170-174
We report on the synthesis of hybrid mesostructured silica from aqueous solutions of C12-Glutamic acid and C12-Leucine based surfactant formulations with sodium silicate under neutral pH and atmospheric conditions. The approach shows
the challenging task of organizing silica from entirely sustainable sources under environmentally benign conditions. 相似文献
167.
Let (ρ λ ) λ∈Λ be a holomorphic family of representations of a finitely generated group G into PSL(2,ℂ), parameterized by a complex manifold Λ. We define a notion of bifurcation current in this context, that is, a positive closed current on Λ describing the bifurcations of this family of representations in a quantitative sense. It is the analogue of the bifurcation current introduced by DeMarco for holomorphic families of rational mappings on ℙ1. Our definition relies on the theory of random products of matrices, so it depends on the choice of a probability measure μ on G. 相似文献
168.
Various sources of uncertainty can arise in metal forming processes, or their numerical simulation, or both, such as uncertainty in material behavior, process conditions, and geometry. Methods from the domain of uncertainty quantification can help assess the impact of such uncertainty on metal forming processes and their numerical simulation, and they can thus help improve robustness and predictive accuracy. In this paper, we compare stochastic methods and interval methods, two classes of methods receiving broad attention in the domain of uncertainty quantification, through their application to a numerical simulation of a sheet metal forming process. 相似文献
169.
170.
Romain Sallio Stéphane Lebrun Francine Agbossou-Niedercorn Christophe Michon Eric Deniau 《Tetrahedron: Asymmetry》2012,23(13):998-1004
Two alternative synthetic approaches to a variety of enantioenriched 6-arylated piperidin-2-ones have been developed. The first one is based on the hydrogenation of suitably arylated chiral cyclic enehydrazides. The second approach relies on the asymmetric catalytic hydrogenation of the corresponding N-alkylated precursors. 相似文献