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101.
Renaud Masson 《International Journal of Solids and Structures》2008,45(3-4):757-769
Except for particular cases, the classical expressions of the Eshelby or Hill polarization tensors, depend, respectively, on a simple or double integral for a fully anisotropic two-dimensional or three-dimensional elastic body. When the body is two-dimensional, we take advantage of Cauchy’s theory of residues to derive a new explicit expression which depends on the two pairs of complex conjugate roots of a quartic equation. If the body exhibits orthotropic symmetry, these roots are explicitly given as a function of the independent components of the elasticity tensor. Similarly, the double integral is reduced to a simple one when the body is three-dimensional. The corresponding integrand depends on the three pairs of complex conjugate roots of a sextic equation which reduces to a cubic one for orthotropic symmetry. This new expression improves significantly the computation times when the degree of anisotropy is high. For both two and three-dimensional bodies, degenerate cases are also studied to yield valid expressions in any events. 相似文献
102.
The identification and quantification of semi-volatile contaminants dissolved in water is currently done in laboratory after a sampling step. This procedure is not satisfactory first because risks of samples contamination and analytes losses remain, in particular when these are present in ultra-trace concentrations, and secondly because procedures are time-consuming. The coupling of the stir bar sorptive extraction (SBSE), a new device of extraction technique, and a new generation of gas chromatography mass spectrometry (GC-MS), the field apparatus EM 640 S from Bruker, could be an answer to the challenge of on-site analysis. This analytical system was used to analyze 24 PAHs, among them 15 EPA priority pollutants. It was shown that this coupling led to encouraging results with LODs around the sub-ppt level for most of the compounds and R.S.D. included between 1 and 48%. The existence of competition phenomena between the various analytes inside the absorbent phase was demonstrated with the release (up to 80%) of light compounds. This result shows the necessity to work on the kinetic domain rather than on the thermodynamic equilibrium that is influenced by nature and concentration of other compounds. The matrix effects were also studied through the comparative analysis of ultrapure water, artificial and natural seawaters spiked with PAHs and the influence of ionic strength and particulate organic matter was investigated. 相似文献
103.
Within the context of turbojet engine re-ignition after in-flight extinction, a thermo-diffusive model has been developed to describe the electrical ignition, at low pressure and low temperature, of a cluster of fuel droplets. The model involves the resolution of the conservation equations of mass, species and energy. It also takes into account the various physical and chemical phenomena occurring during the ignition process. This Note presents the ignition model and preliminary results of this model applied to an experimental configuration. To cite this article: V. Quintilla et al., C. R. Mecanique 330 (2002) 811–818. 相似文献
104.
Brønsted acids catalyze the addition of β-enaminoacrylates to α,β-unsaturated aldehydes leading to substituted dihydropyridines in moderate to good yields under mild conditions. The first example of an enantioselective synthesis of a dihydropyridine is also reported. 相似文献
105.
Bizet V Pannecoucke X Renaud JL Cahard D 《Angewandte Chemie (International ed. in English)》2012,51(26):6467-6470
Transfer news: A synthetic approach to chiral β-CF(3)-substituted saturated carbonyl compounds has been developed in which ruthenium complexes efficiently catalyze the redox isomerization of CF(3)-bearing allylic alcohols by an intramolecular suprafacial enantiospecific 1,3-hydrogen transfer (see scheme). This method was used for the enantioselective synthesis of (S)-CF(3)-citronellol. 相似文献
106.
107.
Christine Bachoc Renaud Coulangeon Gabriele Nebe 《Journal of Algebraic Combinatorics》2002,16(1):5-19
We introduce the notion of a t-design on the Grassmann manifold
of the m-subspaces of the Euclidean space
n
. It generalizes the notion of antipodal spherical design which was introduced by P. Delsarte, J.-M. Goethals and J.-J. Seidel. We characterize the finite subgroups of the orthogonal group which have the property that all its orbits are t-designs. Generalizing a result due to B. Venkov, we prove that, if the minimal m-sections of a lattice L form a 4-design, then L is a local maximum for the Rankin function
n,m
. 相似文献
108.
Dramatic Effect of Magnetite Particles on the Dynamics of Photogenerated Free Radicals 总被引:1,自引:0,他引:1
Abstract— Polymeric particles of about 1 u.m in diameter and containing around 40% magnetite have a dramatic influence on the dynamics of triplet radical pair reactions occurring in micelles in their vicinity. The effect has been monitored with laser flash photolysis techniques and results in a decrease of the number of radicals that separate from their geminate partner and an acceleration of radical pair geminate reactions. The effect involves remote interactions because the solution contains ca 1011 micelles for each polymeric particle. Magnetite also perturbs the way in which the radicals interact with an external magnetic field. 相似文献
109.
Nadira Moufid Philippe Renaud Carla Hassler Bernd Giese 《Helvetica chimica acta》1995,78(4):1006-1012
The stereoselectivity in reactions of 2-oxy-substituted radicals of type B was investigated. As expected, minimization of allylic 1,3-strain was the major controlling factor. Under standard conditions, only a modest level of stereoselectivity was observed. E.g., deuteration of the benzylated radical (R1 = benzyl) gave diastereoisomer ratios ≤ 2:1. Use of a bulky protective group on the O-atom (R1 = (t-Bu)Ph2Si) enhanced slightly the selectivity (ratio 4.1:1). However, a dramatic increase of the stereoselectivity (ratio 13:1) was obtained, when the reaction was performed with the free alcohol after treatment with bulky methylaluminium bis(phenoxide) derivatives (methyl-aluminium bis[2,6-di(tert-butyl)-4-methylphenoxide] (MAD) and methylaluminium bis(2,6-diphenylphenoxide) (MAPH)). 相似文献
110.
Parrot S Sauvinet V Xavier JM Chavagnac D Mouly-Badina L Garcia-Larrea L Mertens P Renaud B 《Electrophoresis》2004,25(10-11):1511-1517
A method originally developed for the separation of the three neurotransmitters gamma-aminobutyric acid (GABA), glutamate (Glu) and L-aspartate (L-Asp) in microdialysis samples from rat brain (Sauvinet et al., Electrophoresis 2003, 24, 3187-3196) was applied to human spinal dialysates obtained during peroperative microdialysis from patients undergoing surgery against chronic pain. Molecules were tagged on their primary amine function with the fluorogene agent, naphthalene-2,3-dicarboxaldehyde (NDA), and, after separation by capillary electrophoresis (CE, 75 mmol/L borate buffer, pH 9.2, containing 70 mmol/L sodium dodecyl sulfate and 10 mmol/L hydroxypropyl-beta-cyclodextrin, + 25 kV voltage), were detected by laser-induced fluorescence detection (LIFD) using a 442 nm helium-cadmium laser. The complete method, including microdialysis sampling and analysis by CE-LIFD, has been validated for the analysis of human spinal microdialysates. The analytical detection limits were 1, 3.7 and 17 nmol/L for GABA, Glu and L-Asp respectively. This method allows an accurate measurement of the three amino acid neurotransmitters during an in vivo monitoring performed as rapidly as every minute in the human spinal dorsal horn. In addition, the effect of a brief peroperative electrical stimulation of the dorsal rootlets was investigated. The results obtained illustrate the advantages of combining microdialysis with CE-LIFD for studying neurotransmitters with such a high sampling rate. 相似文献