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61.
[reaction: see text] Palladium-catalyzed intramolecular allylic alkylations of unsaturated EWG-activated amides can take place under phase-transfer conditions or in the presence of a crown ether. These new reaction conditions are milder and higher yielding than those previously reported. A rationalization for such an unexpected result is put forth and validated by DFT-B3LYP calculations. The results suggest cyclization via a counterion-free (E)-enolate TS. 相似文献
62.
Zhou SZ Sey M De Clercq PJ Milanesio M Viterbo D 《Angewandte Chemie (International ed. in English)》2000,39(16):2861-2863
63.
Gunter S Wolf RC Leuterer F Gruber O Kaufmann M Lackner K Maraschek M Mc Carthy PJ Meister H Peeters A Pereverzev G Salzmann H Schade S Schweinzer J Suttrop W 《Physical review letters》2000,84(14):3097-3100
Internal transport barriers have been demonstrated to exist also under conditions with T(e) approximately T(i) approximately 10 keV and predominant electron heating of the tokamak core region. Central electron cyclotron heating was added to neutral beam injection-heated ASDEX Upgrade discharges with a preexisting internal transport barrier, established through programmed current ramping leading to shear reversal. Compared to a reference internal transport barrier discharge without electron cyclotron resonance heating, the electron heat conductivity in the barrier region was found not to increase, in spite of a fivefold increase in electron heat flux, and also angular momentum and ion energy transport did not deteriorate. 相似文献
64.
We present what we believe are the first experimental results obtained with modal linear predictive control of an adaptive optics system operating on sky at a visible wavelength on a 1.52-m telescope (Observatoire de Haute-Provence, France). This system yields substantially better results than optimized integral control: a 30% relative gain in Strehl ratio is measured, even in conditions of low wind speed. 相似文献
65.
Calderbank AR; Cameron PJ; Kantor WM; Seidel JJ 《Proceedings London Mathematical Society》1997,75(2):436-480
When m is odd, spreads in an orthogonal vector space of type+(2m + 2,2) are related to binary Kerdock codes and extremalline-sets in 2m + 1 with prescribed angles. Spreads in a 2m-dimensionalbinary symplectic vector space are related to Kerdock codesover Z4 and extremal line-sets in with prescribed angles. These connections involve binary, realand complex geometry associated with extraspecial 2-groups.A geometric map from symplectic to orthogonal spreads is shownto induce the Gray map from a corresponding Z4-Kerdock codeto its binary image. These geometric considerations lead tothe construction, for any odd composite m, of large numbersof Z4-Kerdock codes. They also produce new Z4-linear Kerdockand Preparata codes. 1991 Mathematics Subject Classification:primary 94B60; secondary 51M15, 20C99. 相似文献
66.
67.
De Muynck H Madder A Farcy N De Clercq PJ Pérez-Payán MN Öhberg LM Davis AP 《Angewandte Chemie (International ed. in English)》2000,39(1):145-148
Recursive deconvolution of a 729-membered peptide library has identified three active sequences, in which both Ser and His are present in one of the two tripeptidic chains generated on a steroidal scaffold (see structural formula), for the cleavage of an activated p-nitrophenyl ester. This combinatorial approach aims at searching for serine-protease-like activity. 相似文献
68.
The behaviour of the complex of copper with 1,10-phenanthroline at a mercury electrode was investigated in acidic chloride media. Adsorption phenomena were observed by both differential-pulse and normal-pulse polarography. These properties were used in developing a sensitive stripping voltammetric procedurefor the determination of traces of copper. The effects of various operational parameters (pH, ligand concentration, potential and accumulation time) on the reduction current of the adsorbed chelate are discussed. Interferences by other trace metals and organic matter were investigated. A linear current-concentration relationship was observed up to about 1.5 × 10?7 M. The detection limit is 1.2 × 10?10 M copper after a 10-min accumulation time with a stirred solution. 相似文献
69.
Madec F Billaudel B Charlet de Sauvage R Sartor P Veyret B 《Bioelectrochemistry (Amsterdam, Netherlands)》2003,60(1-2):73-80
Several experimental studies have produced contradictory results on the effects of extremely low frequency (ELF) magnetic fields on cellular processes involving calcium ions. Furthermore, the few positive results have not been independently replicated. In most of these studies, isolated cells were used. Our study used mouse islets of Langerhans, in which very regular oscillations of calcium concentration can be observed at length. These oscillations are sustained by processes that imply energetic and inter-intracellular communication. Various magnetic fields were applied, either sinusoidal at different frequencies (50 Hz or multiples of the natural oscillation frequency) at 0.1 or 1 mT or static at 1 mT. Islets were also exposed to "cyclotron resonance" conditions. There was neither alteration of the fundamental oscillation frequency nor the degree of organisation under all exposure conditions. Using this sensitive model, we could not show new evidence of alterations of calcium processes under exposure to various magnetic fields. 相似文献
70.