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排序方式: 共有115条查询结果,搜索用时 15 毫秒
1.
Langer P Armbrust H Eckardt T Magull J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(6):1443-1455
The Lewis acid mediated cyclization of epoxides with 1,3-bis(trimethylsilyloxy)-1,3-butadienes, electroneutral equivalents of 1,3-dicarbonyl dianions, results in the formation of 2-alkylidenetetrahydrofurans with a great variety of substitution patterns and functional groups. This includes the synthesis of 2,3'-bifuranylidenes and 7-oxabicyclo[4.3.0]nonanes. The cyclization of dienes with functionalized epoxides containing base-labile groups proceeds with good chemoselectivity. In all reactions, good regio- and E diastereoselectivities are observed. Based on the stereoselectivities observed for reactions of 1,2-disubstituted epoxides, a working hypothesis for the mechanism of the reaction is suggested. 相似文献
2.
ALI Rahmani Christian B. Eckardt Richard G. Brereton James R. Maxwell 《Photochemistry and photobiology》1993,57(S1):1048-1052
Abstract— This paper reports a new method for monitoring the allomerization reactions of chlorophyll a and pheo-phytin a. Complex mixtures are generated from illuminating pure compounds and monitored using both diode array high-performance liquid chromatography (DAD-HPLC) and liquid chromatography-mass spectrometry (LC-MS). LC-MS allows molecular weight and fragment ion analysis of significant HPLC peaks. Five products of the degradation of chlorophyll a can be simultaneously detected in a mixture, namely the monohydroxy allomer, the methoxylactone allomer, pheophytin a and the two corresponding allomers of the pheophytin. It is demonstrated that more than one pathway must be involved in the in vitro photodegradation of chlorophyll a as shown by the simultaneous existence of several intermediates. 相似文献
3.
Adams MR Aïd S Anthony PL Averill DA Baker MD Baller BR Banerjee A Bhatti AA Bratzler U Braun HM Breidung H Busza W Carroll TJ Clark HL Conrad JM Davisson R Derado I Dhawan SK Dietrich FS Dougherty W Dreyer T Eckardt V Ecker U Erdmann M Faller F Fang GY Figiel J Finlay RW Gebauer HJ Geesaman DF Griffioen KA Guo RS Haas J Halliwell C Hantke D Hicks KH Hughes VW Jackson HE Jancso G Jansen DM Jin Z Kaufman S Kennedy RD Kinney ER Kirk T Kobrak HG Kotwal AV Kunori S Lancaster S Lord JJ Lubatti HJ 《Physical review letters》1995,74(9):1525-1529
4.
Alt C Anticic T Baatar B Barna D Bartke J Betev L Białkowska H Billmeier A Blume C Boimska B Botje M Bracinik J Bramm R Brun R Buncić P Cerny V Christakoglou P Chvala O Cramer JG Csató P Darmenov N Dimitrov A Dinkelaker P Eckardt V Farantatos G Flierl D Fodor Z Foka P Freund P Friese V Gál J Gaździcki M Georgopoulos G Gładysz E Grebieszkow K Hegyi S Höhne C Kadija K Karev A Kliemant M Kniege S Kolesnikov VI Kollegger T Kornas E Korus R Kowalski M Kraus I Kreps M van Leeuwen M Lévai P Litov L 《Physical review letters》2005,94(19):192301
Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models. 相似文献
5.
We demonstrate that the transition from a superfluid to a Mott insulator in the Bose-Hubbard model can be induced by an oscillating force through an effective renormalization of the tunneling matrix element. The mechanism involves adiabatic following of Floquet states, and can be tested experimentally with Bose-Einstein condensates in periodically driven optical lattices. Its extension from small to very large systems yields nontrivial information on the condensate dynamics. 相似文献
6.
We study many-body tunneling of a small Bose-Einstein condensate in a periodically modulated, tilted double-well potential. Periodic modulation of the trapping potential leads to an analog of photon-assisted tunneling, with distinct signatures of the interparticle interaction visible in the amount of particles transferred from one well to the other. In particular, under experimentally accessible conditions there exist well-developed half-integer Shapiro-like resonances. 相似文献
7.
We explore the contributions of inner shell ionization to the energy loss of 7 to 270 keV protons in C and Al foils under experimental conditions such that the product of the observation angle and the projectile energy is kept constant. By normalizing these energy loss measurements to the energy loss in the forward direction we observe a pronounced rising behavior with increasing energy. This effect appears in the same range of energies where the respective K- and L-shell ionization cross sections of these elements show a similar threshold behavior. Based also on various theoretical considerations we interpret these results as clear evidence of the inner shell ionization contribution to the energy loss. 相似文献
8.
F. Eckardt 《Fresenius' Journal of Analytical Chemistry》1915,54(1):53
Ohne Zusammenfassung 相似文献
9.
10.
All known procedures of smoothing are limited by the beginning of falsification of the signals. We suggest a simple modification of the moving average of the polynomial smoothing procedure. The signal curve is smoothed to the best degree and independently of the special problem within an interval calculated from then-th multiple of the standard deviation of the noise.
Zusammenfassung In einigen Fällen (Bildung von Ableitungen, Entschmierungsrechnungen, Auswertung schwacher Effecte) ist auch bei der DSC-Technik eine Glättung des primären Signals angebracht. Alle bekannten Verfahren beinhalten immer einen Kompromiß zwischen erreichter Glättung und beginnender, nicht mehr zu vernachlässigender Verfälschung der Analysenergebnisse. Zudem erfordert jedes Problem seine eigenen optimalen Glättungsparameter. Wir schlagen eine einfache und universell anwendbare Modifikation des Verfahrens mit gleitender Mittelwertsbildung bzw. unter Verwendung der Golay-Sawitzky-Filter vor. In einem Streifen, der aus einem vorgebbaren Vielfachen der Standardabweichung des Rauschens gebildet wird, erhält man so eine optimale Glättung.相似文献