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61.
Summary The mass spectra of sixty lanthanide chelates of the fluorinated -diketones RC(OH)=CHCOCF3 (R=2-theonyl,p-BrC6H4,m-MeC6H4,o-MeC6H4, and Bu-t) have been obtained. The mass spectra were essentially similar, in contrast to those found ford-block transition metal chelates. Valency change from 3 to 2 occurred with samarium (4f
5), europium (4f
6), thulium (4f
12), and ytterbium (4f
13); the intensity of the Met(II)-containing peaks varied: Eu Sm > Yb > Tm, reflecting the decreasing tendency of these lanthanides to display bivalency. Valency change from 4 to 3 was observed with cerium (4f1) but not with terbium (4f8).Part II,Transition Met. Chem., 9, 423 (1984). 相似文献
62.
6MAP is a fluorescent analogue of adenine that undergoes Watson-Crick base pairing and base stacking in double-stranded DNA. The one-photon absorption spectrum of 6MAP is characterized by a maximum around 330 nm with moderate quantum yield fluorescence centered at about 420 nm. To take advantage of this probe for confocal and single-molecule microscopy, it would be advantageous to be able to excite the analogue via two photons. We report the first determination of the two-photon excitation cross section and spectrum for 6MAP from 614 to 700 nm. The power dependence of the fluorescence indicates that emission results from the absorption of two photons. The one-photon and two-photon emission line shapes are identical within experimental error. A study of the concentration dependence of the fluorescence yield for one-photon excitation shows no measurable quenching up to about 5 microM. The maximum in the two-photon excitation spectrum gives a two-photon cross section, delta(TPE), of 3.4 +/- 0.1 Goeppert-Mayer (G.M.) at 659 nm, which correlates well with the one-photon absorption maximum. This compares quite favorably with cross sections of various naturally fluorescent biological molecules such as flavins and nicotiamide. In addition, we have also obtained the two-photon-induced fluorescence emission spectrum of quinine sulfate. It is approximately the same as that for one-photon excitation, suggesting that two-photon excitation of quinine sulfate may be used for calibration purposes. 相似文献
63.
Choosing the maximum value from a sequence ofN independent values is a well known problem often called the candidate problem or secretary problem. This paper treats the above problem with a discount penalty (0<<1) for each additional observation taken. It is shown that asN increases indefinitely, the optimal stopping policy is bounded although the maximum expected payoff goes to zero, and that there exists a sequence 0=
0<1<2<<1, such that the asymptotic optimal stopping rule is the same for all
i–1<i. 相似文献
64.
65.
A variety of cephalosporins have been converted into the corresponding 2-alkoxy derivatives using ceric ammonium nitrate in the appropriate alcohol. 相似文献
66.
67.
Podobnik Boris Jusup Marko Wang Zhen Stanley H. Eugene 《Journal of statistical physics》2017,167(3-4):1007-1019
Journal of Statistical Physics - Mutualistic relationships among the different species are ubiquitous in nature. To prevent mutualism from slipping into antagonism, a host often invokes a... 相似文献
68.
Demulsification of water-in-crude oil emulsion was studied at two different salinities, 0.5% and 10% sodium chloride, using five different nonionic surfactants. Equilibrium crude oil-water interfacial tension was measured with drop volume method. Low molecular weight surfactants were found to be completely ineffective as demulsifiers. Three surfactants which were effective demulsifiers, exhibited good interfacial activity, surface adsorption and surface pressure. The performance of the demulsifiers changed with change in salinity of aqueous phase. Surfactants effective as demulsifiers reduced surface tension of water by more than 25 dynes-cm-1. For a given crude oil-water system, the surfactant which developed surface pressure in excess of 15 dynes-cm-1 was found to be good demulsifier for that system. Based upon these studies, a physical model of demulsification has been proposed 相似文献
69.
70.
In this paper we address the existence of smooth manifolds proper homotopy equivalent to nonuniform arithmetic manifolds M = Γ\G/K that are not homeomorphic to it. While the manifolds M are properly rigid if rankℚ(Γ) ≤ 2, we show that the so‐called virtual structure group has infinite rank as a ℚ‐vector space if rankℚ(Γ) ≥ 4.© 2015 Wiley Periodicals, Inc. 相似文献