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51.
Bryant WS Jones JW Mason PE Guzei I Rheingold AL Fronczek FR Nagvekar DS Gibson HW 《Organic letters》1999,1(7):1001-1004
[formula: see text] Inspired by folded, nonpseudorotaxane complexes of bis(m-phenylene)-32-crown-10 systems, we synthesized a new bicyclic crown ether containing two 1,3,5-phenylene units linked by three tetra(ethyleneoxy) units. The new cryptand forms a "pseudorotaxane-like" inclusion complex with N,N'-dimethyl-4,4'-bipyridinium bis(hexafluorophosphate) with association constant Ka = 6.1 x 10(4) M-1, 100-fold greater than that of an analogous simple crown ether. 相似文献
52.
Unique "cradled barbell" complex between a secondary diammonium ion and bis(m-phenylene)-32-crown-10
[formula: see text] The complexation between N,N'-dibenzyl(m-xylylene)diammonium bis(hexafluorophosphate) (2) and bis(m-phenylene)-32-crown-10 (5) was shown to occur in solution by nuclear magnetic resonance with 1:1 stoichiometry and a Ka value of 189 +/- 19 M-1. A crystal structure of 2:5 revealed a unique 1:1 "exo" or "cradled barbell" complex, instead of the expected pseudorotaxane. This unexpected result illustrates that caution be used in interpreting the results from these types of complexes in the solution and "gas" phases on the basis of crystal structures. 相似文献
53.
Continuous-wave optical parametric oscillator based on periodically poled KTiOPO(4) and its application to spectroscopy 总被引:1,自引:0,他引:1
We report a continuous-wave, doubly resonant optical parametric oscillator (OPO) based on the nonlinear material periodically poled KTiOPO(4) and its application to spectroscopy. The OPO, which is pumped by a diode-pumped frequency-doubled Nd:YLF laser at 523 nm, has a low pump-power threshold of 25 mW and can deliver 10 mW of single-frequency output at 1.65 mum for a pump power of 200 mW. The idler wavelength can be temperature tuned at a rate of 0.73 nm/( degrees )C , and smooth tuning of the output frequency over ~3 GHz is achieved by smooth tuning of the pump laser. We demonstrate the practicality of the OPO by recording the absorption spectrum of methane near 1649 nm. 相似文献
54.
This paper describes a case study relating to a food-processing plant. The methods used to address the case include spreadsheets combined with Goldratt's Theory of Constraints (TOC), both of which are accessible to practising managers. The paper demonstrates how standard spreadsheet optimisation tools can be used in combination with a TOC framework to provide effective decision aids. The results from the case study indicate real productivity improvements are possible from even small models of a situation. The paper explores the interrelationships and complementaries between Linear Programming and Theory of Constraints frameworks, and details the steps involved in using them in combination. We argue that traditional LP practice should be modified in light of the ease with which LPs can be solved, and suggest that the Theory of Constraints approach provides a useful framework to guide LP use. We share some of the insights gained both by the analysts and by the company. 相似文献
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57.
Far-infrared absorption spectra of H216O, H218O, H16OD, H18OD, D216O, D218O have been observed between 10 and 40 cm?1 at a resolution of 0.07 cm?1. Experimental and calculated line positions agree within the accuracy of the experiment (±0.003 cm?1). The relative intensities of type a and type b transitions of H16OD and H18OD are used to estimate the ratio . 相似文献
58.
Abstract— The bioluminescent enzyme from Photobacterium fischeri is normally activated in vifro by reaction with FMNH2 and O2 . in the presence of a long-chain aldehyde. Emission from enzyme intermediates in this reaction continues for several seconds, and if the mixture is frozen just after initiation of the reaction, this presumptive emission may be delayed until the system is warmed again. Light is then emitted in a fashion analogous to thermo-luminescent emission, with a maximum intensity at — 10°C. The experiments described here show that the total amount of light which is emitted under these conditions no longer depends so much upon aldehyde, a relatively high quantum yield being obtained both with and without aldehyde.
It is further shown that bioluminescence may be activated by light, populating it is believed, the same state which is responsible for the emission in the case of the FMNH2 -induced emission. The light-induced reaction does not depend on flavin in the enzyme preparations, nor does the activation spectrum resemble that of a flavoprotein. Activation may be carried out in the solid state at temperatures down to at least — 100°C, and so does not involve the diffusion of large molecules. It is proposed that energy storage takes place by charge separation, and that the excited state from which emission takes place is associated with charge recombination. 相似文献
It is further shown that bioluminescence may be activated by light, populating it is believed, the same state which is responsible for the emission in the case of the FMNH
59.
Thomas Gibson 《Tetrahedron letters》1982,23(2):157-158
Hydrozirconation of internal olefins followed by oxidation with anhydrous t-butyl hydroperoxide generates primary alcohols in good yields and high purity. 相似文献
60.
Within the framework of a Faddeev formalism and an implicit hyperon channel approximation, we have calculatedK ? d elastic, total, and reaction cross sections for incident kaon laboratory momenta up to 120 Mev/c. We have used as input two different (slightly modified) multichannelM matrix fits to low-energy¯KN scattering, each of which contains explicitly theπ Y channels, as well as a single channel representation of the¯KN interaction in which the hyperon channels appear only through their contributions to the imaginary parts of the¯KN scattering lengths. TheK ? d cross sections obtained with the single channel¯KN input differ by only some 10% from those for which we used the multichannel¯KN input. TheK ? d cross sections calculated using¯KN input parameters from each of the two separateM matrix fits differ across the entire momentum range investigated by 25–35%. 相似文献