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71.
Jalce G Seck M Franck X Hocquemiller R Figadère B 《The Journal of organic chemistry》2004,69(9):3240-3241
trans-2,5-Disubstituted tetrahydrofurans were obtained as major diastereomers (trans/cis ratio 90:10-100:0) when acetylated gamma-lactols derived from (S)-glutamic acid were treated with titanium enolates of N-acetyl (R)-oxazolidin-2-thiones. A simple transesterification allowed us to obtain the corresponding methyl esters and recover the chiral auxiliary. 相似文献
72.
Ammar A Ménétrier M Villesuzanne A Matar S Chevalier B Etourneau J Villeneuve G Rodríguez-Carvajal J Koo HJ Smirnov AI Whangbo MH 《Inorganic chemistry》2004,43(16):4974-4987
The electronic and structural properties of potassium hexaboride, KB(6), were examined by transport, magnetic susceptibility, EPR, and NMR measurements, temperature-dependent crystal structure determination, and electronic band structure calculations. The valence bands of KB(6) are partially empty, but the electrical resistivity of KB(6) reveals that it is not a normal metal. The magnetic susceptibility as well as EPR and NMR measurements show the presence of localized electrons in KB(6). The EPR spectra of KB(6) have two peaks, a broad ( approximately 320 G) and a narrow (less than approximately 27 G) line width, and the temperature-dependence of the magnetic susceptibility of KB(6) exhibits a strong hysteresis below 70 K. The temperature-dependent crystal structure determination of KB(6) shows the occurrence of an unusual variation in the unit cell parameter hence supporting that the hysteresis of the magnetic susceptibility is a bulk phenomenon. The line width DeltaH(pp) of the broad EPR signal is independent of temperature and EPR frequency. This finding indicates that the line broadening results from the dipole-dipole interaction, and the spins responsible for the broad EPR peak has the average distance of approximately 1.0 nm. To explain these apparently puzzling properties, we examined a probable mechanism of electron localization in KB(6) and its implications. 相似文献
73.
Duan Li Ou Pierre M. Chevalier Iain A. Mackinnon Katsuya Eguchi Ronald Boisvert Kai Su 《Journal of Sol-Gel Science and Technology》2003,26(1-3):407-412
Silicon containing materials have traditionally been used in microelectronic fabrication. Semi-conductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements forming an integrated circuit. These interconnect levels are typically separated by an insulating or dielectric film. Previously, a silicon oxide film was the most commonly used material for such dielectric films having dielectric constants (k) near 4.0. However, as the feature size is continuously scaling down, the relatively high k of such silicon oxide films became inadequate to provide efficient electrical insulation. As such, there has been an increasing market demand for materials with even lower dielectric constant for Interlayer Dielectric (ILD) applications, yet retaining thermal and mechanical integrity. We wish to report here our investigations on the preparation of ultra-low k ILD materials using a sacrificial approach whereby organic groups are burnt out to generate low k porous ORMOSIL films. We have been able to prepare a variety of organically modified silicone resins leading to highly microporous thin films, exhibiting ultra-low k from 1.80 to 2.87, and good to high modulus, 1.5 to 5.5 GPa. Structure property influences on porosity, dielectric constant and modulus will be discussed. 相似文献
74.
75.
K. Noble A.B. Seddon M.L. Turner P. Chevalier I.A. Mackinnon 《Journal of Sol-Gel Science and Technology》2000,19(1-3):807-810
We report the preparation of polysiloxane-modified mesoporous silica gels derived from the acid catalysed hydrolysis of tetraethoxysilane (TEOS) and oligomeric silanol terminated polydimethylsiloxane (PDMS) in the presence of the non-ionic surfactant, octaethylene glycol monohexadecyl ether. The gels were characterised using thermal gravimetric analysis (TGA), infra-red (IR) spectroscopy, X-ray diffraction (XRD) and 29Si solid state cross-polarisation (CP) magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. TGA and IR spectroscopy showed the loss of surfactant after calcination and a decrease in the Si–OH band at 950 cm–1 indicated further condensation had occurred. This was confirmed by the increase in Q4 at –110 ppm, in 29Si MAS NMR spectroscopy, which also showed that calcination had led to the redistribution of PDMS forming a T species. XRD data showed ordering within the structure, with an initial d-spacing of 45 Å, decreasing to 35 Å after calcination. 相似文献
76.
Robert Choukroun Pierre Moumboko Sandrine Chevalier Michel Etienne Bruno Donnadieu 《Angewandte Chemie (International ed. in English)》1998,37(22):3169-3172
At least three different cationic species arise in the classic protonolysis of [VIV(NEt2)4] with a borate ammonium salt. The unexpected formation of the vanadium(V ) species [V(NEt2)4][B(C6H5)4] (shown in the picture without its counterion) underlines the problem of deducing the true oxidation state of vanadium species in Ziegler–Natta reactions. 相似文献
77.
M. Sylla D. Rou de R. Chevalier X. Nguyen Phu G. Rivoire 《Optics Communications》1992,90(4-6):391-398
We have observed a very strong nonlinear absorption in BSO and BGO crystals when they are illuminated by picosecond laser pulses with optical intensity on the order of 108 W/cm2. In addition, a phase conjugate reflectivity of 2×10-3 is obtained in a degenerate four-wave mixing (DFWM) experiment using the same optical power. We derive the nonlinear coupled-wave equations to explain the experimental results. We show that the creation of the conjugate wave can be explained by the presence of a strong nonlinear absorption. 相似文献
78.
H. Caps H. Decauwer M.-L. Chevalier G. Soyez M. Ausloos N. Vandewalle 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):115-119
We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a
Hele-Shaw cell. The bubble edge width ℓ is measured by image analysis. The penetration of the liquid in the foam, the foam
imbibition, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes. The motion of bubbles
needed for the foam inflation is a slow two-dimensional process with respect to the one-dimensional capillary rise of liquid.
The foam is found to imbibes faster than it inflates.
Received 20 May 2002 / Received in final form 21 January 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: herve.caps@ulg.ac.be 相似文献
79.
80.
Lucien Chevalier 《Journal of Fourier Analysis and Applications》2001,7(2):189-198
The aim of this article is to give a new proof of the Lp-inequalities for the Littlewood-Paley g*-function. Our main tool is a pointwise equality, relating a function f, and the associated functional g*(f), which has the form f2=h(f)+g * 2 (f), where h(f) is an explicit function. We obtain this equality as a particular case of a more general one, which is reminiscent of a well-known identity in the stochastic calculus setting, namely the Itô formula. Once the above equality is proved, Lp-estimates for g*(f) are obviously equivalent to Lp/2-estimates for h(f). We obtain these last estimates (more precisely, Hp/2-estimates for h(f) by using a slight extension of the Coifman-Meyer-Stein theorem relating the so-called tent-spaces and the Hardy spaces. We observe that our methods clearly show that the restriction p>2n/n+1 is closely related to cancellation and size properties of the gradient of the Poisson kernel. 相似文献