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81.
82.
Karsten Krohn 《Tetrahedron letters》1980,21(37):3557-3560
Naturally occurring quinones such as 7-methyljuglone, chrysophanol, emodin, helminthosporin, phomarin and physcion were prepared via Diels-Alder reaction and PCC-oxidation of the allylic alkohols obtained from the adducts. 相似文献
83.
84.
The multiphoton ionization (MPI) spectrum of toluene arising from the 1B2 (1Lb) valence state has been investigated. The state participates as a two-photon resonance. A total of nine excited state fundamentals have been characterized, including three non-totally symmetric vibrations. The toluene MPI spectrum shows a strong resemblance to the two-photon fluorescence excitation spectrum with the strongest transitions taking place to the origin and excited state modes ν1(a1), ν12(a1) and ν14(b)2). The intensities of the observed fundamentals are rationalized in terms of Franck-Condon and vibronic coupling effects. A major conclusion is, that the primary mechanism for the activity of ν12 is vibronic coupling. 相似文献
85.
86.
87.
Luuk H. Karsten 《Physics letters. [Part B]》1981,104(4):315-319
A very short proof of a no-go theorem for putting fermions on a lattice is given using the Poincaré-Hopf theorem. The no-go theorem forbids the lattice formulation of theories with handed fermions without species doubling. Examples of such theories are chiral invariant QCD and the Weinberg-Salam-Glashow model. We give arguments why it could be possible to circumvent the no-go theorem by relaxing one of the assumptions, viz. bilinearity of the action in the fermion fields. 相似文献
88.
Al-Anber M Vatsadze S Holze R Lang H Thiel WR 《Dalton transactions (Cambridge, England : 2003)》2005,(22):3632-3637
Electrochemical reduction potentials of a broad selection of nitrogen-containing molecules suitable as bridging (dipodal and tripodal) ligands in coordination and organometallic chemistry are reported and compared with results of semiempirical calculations. Trends of electrode potentials observed experimentally agree with respective calculated data, deviations can be explained by invoking peculiarities of the involved molecular orbitals and ligand-electrode surface interactions. 相似文献
89.
We consider the effect of distributed delays in predator-prey models and ecological food webs. Whereas the occurrence of delays in population dynamics is usually regarded a destabilizing factor leading to the extinction of species, we here demonstrate complementarily that delay distributions yield larger stability regimes than single delays. Food webs with distributed delays closely resemble nondelayed systems in terms of ecological stability measures. Thus, we state that dependence of dynamics on multiple instances in the past is an important, but so far underestimated, factor for stability in dynamical systems. 相似文献
90.
We develop the general nonequilibrium theory of transport through a quantum dot, including Coulomb blockade effects via a 1/N expansion, where N is the number of scattering channels. At lowest order we recover the Landauer formula for the current plus a self-consistent equation for the dot potential. We obtain the leading corrections and compare with earlier approaches. Finally, we show that to leading and to next leading order in 1/N there is no interaction correction to the weak localization, in contrast to previous theories, but consistent with experiments by Huibers et al. [Phys. Rev. Lett. 81, 1917 (1998)], where N=4. 相似文献