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141.
The direct regioselective C–H arylation of 3-methoxythiophene and 3,4-ethylenedioxythiophene (EDOT) was performed successfully under ‘Heck-type’ experimental conditions. This novel synthetic methodology has been used to prepare in a more simple way a series of oligothiophenes interesting for the electronic industry to build new synthetic organic materials. 相似文献
142.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
143.
We inquire into the time evolution of quantum systems associated with pseudo-or quasi-Hermitian Hamiltonians. We obtain, in
the pseudo-Hermitian case, a generalized Liouville-von Neumann equation for closed systems. We show that quantum systems with
quasi-Hermitian Hamiltonians admit the proper interpretation in terms of open quantum system and derive a generalized Lindblad-Kossakowski
equation. Finally, we extend such formalism to the study of decaying systems.
Partially supported by PRIN “Sintesi”. 相似文献
144.
Electron spin resonance spectra of Mn2+ in diluted solid solutions of MnO2 in Y2O3 have been studied at room temperature for Mn concentrations between 0.20 and 2.00 mol%. Isolated Mn2+ ions in sites with two different symmetries were observed, as well as Mn2+ ions coupled by the exchange interaction. The relative concentration of isolated to coupled Mn2+ ions decreases with increasing manganese concentration. The results are consistent with the assumption that the manganese ions occupy preferentially the C2 symmetry sites. A theoretical calculation based on this model yields an effective range of the exchange interaction between Mn2+ ions of 0.53 nm, of the same order as that of Mn2+ ions in CaO. 相似文献
145.
D. De Salvador A. Coati E. Napolitani M. Berti A.V. Drigo M.S. Carroll J.C. Sturm J. Stangl G. Bauer L. Lazzarini 《Applied Physics A: Materials Science & Processing》2002,75(6):667-672
In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC
layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N2) or oxidizing (O2) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under
oxidation enhances the C diffusion with respect to the N2-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the
layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration.
This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act
as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion
is discussed.
Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002 相似文献
146.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
147.
An overview of theoretical and experimental studies of the coherent type-B e
+
e-pair production by photons in aligned crystals performed at Nuclear Physics Institute at Tomsk Polytechnic University is given. 相似文献
148.
S.-Y. Sheu D.-Y. Yang H.L. Selzle E.W. Schlag 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):557-563
Charge transport is one important example of signal transduction in a protein which is responsible for action at a distance,
and is a fundamental process in biochemical action. A model is presented in which electronic effects interact with motional
processes to combine into a bifunctional model. This model is investigated with new detailed molecular dynamics calculations
and successfully explains such action at a distance.
Received 1st February 2002 / Received in final form 26 May 2002 Published online 13 September 2002 相似文献
149.
N. L. Dmitruk O. Yu. Borkovskaya R. V. Konakova I. B. Mamontova S. V. Mamykin D. I. Voitsikhovskiy 《Technical Physics》2002,47(6):698-702
The effect of 60Co gamma irradiation at doses of 103-2×105 Gy on the photoconversion and dark I-V characteristics of Au/GaAs surface-barrier solar cells (SCs) is studied. The morphology of the interface microrelief is varied
to reach the highest photoconversion efficiency. Of the two types of microrelief morphology (dendritic and quasi-grating)
obtained by the chemical anisotropic etching of n-(100)GaAs, the latter is more promising, particularly for SCs designed for space application, since the associated SCs offer
higher efficiency and radiation resistance. 相似文献
150.