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991.
992.
The role of various magnetic interchain couplings is investigated by numerical methods in doped frustrated quantum spin chains. A nonmagnetic dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The formation of a local magnetic moment is analyzed in terms of soliton confinement. A four-spin coupling which might originate from cyclic exchange is shown to produce such a confinement. Dopants on different chains experience an effective space-extended nonfrustrating pairwise spin interaction. 相似文献
993.
We study the stress response to a steady imposed shear rate in a concentrated suspension of colloidal particles. We show that, in a small range of concentrations and shear rates, stress exhibits giant fluctuations. The amplitude of these fluctuations obeys a power-law behavior, up to the apparition of a new branch of flow, leading to an excess of high amplitude fluctuations which exhibit a well-defined periodicity. 相似文献
994.
Schoeller WW Rozhenko A Bourissou D Bertrand G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(15):3611-3617
The concept of through-space versus through-bond interactions on the stabilization of biradical structures with a singlet or triplet ground state is evaluated for the 1,3-diboracyclobutane-1,3-diyls and related congeners. Singlet biradicals are favored when the intermediate units E feature singlet character (PH(2) (+), AsH(2) (+)), while E fragments with triplet character (NH(2) (+)) induce small energy separations between the lowest singlet and triplet states. These considerations are supported by quantum chemical calculations with energy optimization at 1) MCSCF level plus MR-MP2 correction, 2) MR-MP2 level, and 3) two different types of density functional levels for the planar (D(2h)) geometries. The singlet-triplet energy separations in the planar compounds increase with increasing singlet stability of the corresponding E fragments. In addition to this newly developed principal features for singlet stabilization, which primarily occurs in bonded structures with higher main-group elements, the corresponding valence isomers with bicyclobutane, cyclobutene and cis-butadiene structures are investigated. 相似文献
995.
Delabouglise D Marcus B Mermoux M Bouvier P Chane-Tune J Petit JP Mailley P Livache T 《Chemical communications (Cambridge, England)》2003,(21):2698-2699
Grafting of biotin on top of a polycrystalline boron-doped diamond layer was achieved by surface oxidation followed by an esterification reaction and revealed by fluorescently labelled streptavidin. 相似文献
996.
Three generations of bidentate phosphinated Pd(II) dendrimers are efficient catalysts in the absence of copper co-catalyst for the Sonogashira reaction and are, with two cyclohexyl substituents on the phosphorus atoms, recovered by precipitation and re-used. 相似文献
997.
998.
Didier Villemin 《Tetrahedron letters》1980,21(18):1715-1718
Two syntheses of macrolides olefin methathesis are presented. The first (A) involves preparation of ω-hydroxyacid or by metathesis followed by cyclisation, while the second (B) involves macrocyclic ring closure by metathesis of a ω,ω′diunsaturated ester . 相似文献
999.
The aim of this Letter is to show that the Poincare-Dulac theorem for holomorphic finite-dimensional representation, is valid for any nilpotent Lie algebrag. We reduce the classification problem of representations with a semisimple linear part satisfying the Poincaré condition to an algebraic problem. We develop a complete computation in a particular case. 相似文献
1000.