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91.
An unexpected directing effect in the asymmetric transfer hydrogenation of α,α-disubstituted ketones
α,α-Disubstituted ketones containing an aromatic ring or alkene are reduced in high enantiomeric excess using an asymmetric transfer hydrogenation catalyst. The sense of reduction indicates that the unsaturated region of the ketone adopts a position adjacent to the Ru-bound η(6)-arene ring in the reduction transition state. 相似文献
92.
Khare A Wills AW Ammerman LM Norris DJ Aydil ES 《Chemical communications (Cambridge, England)》2011,47(42):11721-11723
Starting with metal dithiocarbamate complexes, we synthesize colloidal Cu(2)ZnSnS(4) (CZTS) nanocrystals with diameters ranging from 2 to 7 nm. Structural and Raman scattering data confirm that CZTS is obtained rather than other possible material phases. The optical absorption spectra of nanocrystals with diameters less than 3 nm show a shift to higher energy due to quantum confinement. 相似文献
93.
We investigate the possibility of embedding the vector curvaton paradigm in D-brane models of inflation in type IIB string theory in a simple toy model. The vector curvaton is identified with the U(1) gauge field that lives on the world volume of a D3-brane, which may be stationary or undergoing general motion in the internal space. The dilaton is considered as a spectator field which modulates the evolution of the vector field. In this set-up, the vector curvaton is able to generate measurable statistical anisotropy in the spectrum and bispectrum of the curvature perturbation assuming that the dilaton evolves as e−?∝a2 where a(t) is the scale factor. Our work constitutes a first step towards exploring how such distinctive features may arise from the presence of several light fields that naturally appear in string theory models of cosmology. 相似文献
94.
Benniston AC Winstanley TP Lemmetyinen H Tkachenko NV Harrington RW Wills C 《Organic letters》2012,14(6):1374-1377
The synthesis of dyes based on a highly substituted terephthalic acid core is described, starting from readily available 2,5-dihydroxy-terephthalic acid diethyl ester. The dyes are highly colored, soluble in organic solvents and reasonably fluorescent in solution and in the solid state. The maxima for absorption and emission are around 402 and 502 nm, respectively. The fluorophores are readily cyclized to generate compounds which comprise the basic 6,13-dihydroxy-chromeno[2,3-b]xanthene-7,14-dione unit. These new derivatives are nonfluorescent. 相似文献
95.
B Fåk E Kermarrec L Messio B Bernu C Lhuillier F Bert P Mendels B Koteswararao F Bouquet J Ollivier AD Hillier A Amato RH Colman AS Wills 《Physical review letters》2012,109(3):037208
Magnetic susceptibility, NMR, muon spin relaxation, and inelastic neutron scattering measurements show that kapellasite, Cu_{3}Zn(OH)_{6}Cl_{2}, a geometrically frustrated spin-1/2 kagome antiferromagnet polymorphic with herbertsmithite, is a gapless spin liquid showing unusual dynamic short-range correlations of noncoplanar cuboc2 type which persist down to 20?mK. The Hamiltonian is determined from a fit of a high-temperature series expansion to bulk susceptibility data and possesses competing exchange interactions. The magnetic specific heat calculated from these exchange couplings is in good agreement with experiment. The temperature dependence of the magnetic structure factor and the muon relaxation rate are calculated in a Schwinger-boson approach and compared to experimental results. 相似文献
96.
97.
98.
J.M.F. Labastida M. Roček E. Sánchez-Velasco Peter Wills 《Physics letters. [Part B]》1985,151(2):111-114
We construct the full N = 2 supergravity action in terms of N = 1 supergravity and matter fields. 相似文献
99.
100.
Luis Alberto Wills Toro 《Zeitschrift fur Physik C Particles and Fields》1992,56(4):629-634
We study models including renormalizable and nonrenormalizable polynomial interactions. We derive the partial differential equations, which are relevant for the variation of parameters of the model. A supersymmetric model is considered as example. 相似文献