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71.
A regio- and steroselective conversion of the totally synthetic 3α, 18-di-O-benzyl-17-nor-14-aphidicolen-16-one (5), into (±)-aphidicolin 1 , by hydroxylation of the 2-methylidenebicyclo[3.2.1] oct-3-ene derivative 6 is described. Compound 5 was a key intermediate in our previously described total synthesis of 2 , which represented a formal synthesis of 1 . 相似文献
72.
C60 inclusion complexes in γ-cyclodextrin are studied by molecular mechanics and semi-empirical methods with the aim of comparing measured and calculated induced circular dichroism (ICD) spectra. Low energy geometries of the complexes are generated by Monte Carlo simulations, also accounting for solvation effects by an aqueous environment. The ICD spectrum of the complex is then obtained from an exciton model based on semi-empirical calculations of the transition energies and the corresponding transition moments. Highly symmetric, tightly bound complexes of two γ-cyclodextrins and buckminsterfullerene are found as the most probable structures. The main bands of the experimentally derived ICD spectrum are assigned to the excitation transitions of the chromophore and are discussed in comparison to calculations on the magnetic circular dichroism (MCD) spectrum of C60. 相似文献
73.
The isotope shift in the proton magnetic resonance of deuteromethanes has been examined. By the use of Pople's formula for the chemical shift, it has been shown that the effect is due to vibronic coupling from the bending modes S4. The chemical shift was evaluated under the assumption that the hydrogen population is linearly dependent on the 2S character of the bonded carbon hybrid. Satisfactory agreement between theoretical and experimental results was obtained. 相似文献
74.
Salvatore Pignataro Giovanni Marletta Orazio Puglisi Umberto Costantino Giulio Alberti 《Journal of Electron Spectroscopy and Related Phenomena》1982,25(1):49-57
Mg Kα ESCA spectra of several α-Zr(PO4)2M2 compounds (M = Li+, Na+, K+, Cs+) have been obtained. Satellite structure is observed at ~7–8 eV from the main P 2s peak (corresponding to ~15–16 eV from the main Zr 3d peak). The intensity of the satellite depends on the counter-ion intercalated. For a given counter-ion it is strongly increased by sputtering, the rate of increase being also dependent on the counter-ion. This observation is interpreted mainly in terms of electron-defect formation similar to that involved in the formation of colour centres by radiation damage, and subsequent charge-transfer shake-up of the trapped electrons to the electron-deficient phosphorus or Zr(IV) centres. 相似文献
75.
Umberto Cerruti 《Journal of Mathematical Analysis and Applications》1983,94(2):312-327
It is shown that the category of complete L-similarities on L-sets is a full reflective subcategory of (L) (L-fuzzy graphs); is equivalent to (L)(sheaves on L). Connections with other known “fuzzy” categories are also studied. 相似文献
76.
Summary In this paper we study the Dirichlet problem for the minimal surface equation in a open set Ω without any assumption about
the regularity of ϖΩ. We prove an existence theorem using only the pseudoconvexity of Ω.
Riassunto In questo lavoro studiamo il problema di Dirichlet per l'equazione delle superfici minime in un aperto Ω diR n sulla cui frontiera non si fa nessuna ipotesi di regolarità. Si ottiene un teorema di esistenza usando la sola pseudoconvessità di Ω.相似文献
77.
Canevali C Mari CM Mattoni M Morazzoni F Nodari L Ruffo R Russo U Scotti R 《The journal of physical chemistry. B》2005,109(15):7195-7202
The mechanism of NO interaction with nanosized Ru(Pd,Pt)-doped SnO(2) was studied by electron paramagnetic resonance, M?ssbauer, and electric resistance measurements. Three steps were proposed for the reaction between the semiconductor oxide and the gaseous component: (i) the formation of bielectronic oxygen vacancies (V(o)) in SnO(2); (ii) their single-ionization (V(o)(*)) with injection of electrons into the SnO(2) conduction band; (iii) the subsequent transfer of electrons from V(o)(*) to [Ru(Pd,Pt)](4+). The last process induces the formation of further oxygen vacancies which reduce the transition metal centers to lower oxidation states; the redox processes is enhanced and the electrical resistance in transition metal-doped SnO(2) is stronger modified with respect to the undoped material. 相似文献
78.
Filevich J Rocca JJ Marconi MC Moon SJ Nilsen J Scofield JH Dunn J Smith RF Keenan R Hunter JR Shlyaptsev VN 《Physical review letters》2005,94(3):035005
We present clear experimental evidence showing that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft x-ray wavelengths. We report anomalous fringe shifts in soft x-ray laser interferograms of Al laser-created plasmas. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low charge ions to the index of refraction. This usually neglected bound electron contribution can affect the propagation of soft x-ray radiation in plasmas and the interferometric diagnostics of plasmas for many elements. 相似文献
79.
Luther BM Wang Y Larotonda MA Alessi D Berrill M Marconi MC Rocca JJ Shlyaptsev VN 《Optics letters》2005,30(2):165-167
We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain-length product GL of 15.5 is obtained in the 4d 1S0-4p 1P1 laser line of Ni-like Mo in plasmas heated at grazing incidence with approximately 1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm. 相似文献
80.
Vaschenko G Brizuela F Brewer C Grisham M Mancini H Menoni CS Marconi MC Rocca JJ Chao W Liddle JA Anderson EH Attwood DT Vinogradov AV Artioukov IA Pershyn YP Kondratenko VV 《Optics letters》2005,30(16):2095-2097
Images with a spatial resolution of 120-150 nm were obtained with 46.9 nm light from a compact capillary-discharge laser by use of the combination of a Sc-Si multilayer-coated Schwarzschild condenser and a free-standing imaging zone plate. The results are relevant to the development of compact extreme-ultraviolet laser-based imaging tools for nanoscience and nanotechnology. 相似文献