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11.
Two chromogenic monoaza crown ethers were synthesized and investigated for their lithium extraction capabilities. The chromogenic monoaza 14-crown-4 compound exhibited the best selectivity for lithium over sodium; ca. 2800, with a detection limit of 0.08 ppm. 相似文献
12.
C. H. Wilcox 《Mathematical Methods in the Applied Sciences》1979,1(1):70-88
Pulse mode sonar operation is analyzed under the assumption that the scattering object Γ lies in the far fields of both the transmitter and the receiver. It is shown that, in this approximation, the sonar signal is a plane wave s(x · θ0 – t) near Γ, where θ0 is a unit vector directed from the transmitter toward Γ, and similarly the echo is a plane wave e(x · θ – t) near the receiver, where θ is a unit vector directed from Γ toward the receiver. Moreover, if Γ is stationary with respect to the sonar system then it is shown that where ?(ω) is the Fourier transform of S(τ) and T+(ωθ,ωθ0) is the scattering amplitude in the direction θ due to the scattering by Γ of a time-harmonic plane wave with frequence ω and propagation direction θ0. A generalization of this relation is derived for moving scatterers. 相似文献
13.
M. Amélia Santos Adelino Afonso M. Matilde Marques Craig Wilcox 《Supramolecular chemistry》2013,25(3):201-215
Abstract New receptors based upon a carboxamidonaphthyridine unit derivatized with the polyaromatic segments [4-(1-pyrenyl)butyroylamino] and [3-(9-anthracenyl)propanoylamino] have been synthesized and studied by 1H NMR titration in their binding interaction to the guanosine-C8 adducts from the carcinogens 2-acetylaminofluorene and 2-aminofluorene. The high binding energy, in comparison with that of the non-derivatized analogues, is rationalized in terms of a bi-site interaction (hydrogen bonding and aromatic stacking). Although many factors may contribute to the strength of the host-guest complexes described herein, it appears that in some cases π-π interaction may induce a concomitant bending in the hydrogen bond system. 相似文献
14.
We apply random matrix theory to compare correlation matrix estimators C obtained from emerging market data. The correlation matrices are constructed from 10 years of daily data for stocks listed on the Johannesburg stock exchange (JSE) from January 1993 to December 2002. We test the spectral properties of C against random matrix predictions and find some agreement between the distributions of eigenvalues, nearest neighbour spacings, distributions of eigenvector components and the inverse participation ratios for eigenvectors. We show that interpolating both missing data and illiquid trading days with a zero-order hold increases agreement with RMT predictions. For the more realistic estimation of correlations in an emerging market, we suggest a pairwise measured-data correlation matrix. For the data set used, this approach suggests greater temporal stability for the leading eigenvectors. An interpretation of eigenvectors in terms of trading strategies is given, as opposed to classification by economic sectors. 相似文献
15.
16.
Walter Wilcox 《Annals of Physics》1982,139(1):48-67
The gravitational anomalous magnetic moment of a spin particle is calculated and compared with an earlier dimensional regularization result. The answers disagree although both agree the answer is finite. It is argued that this quantity is not uniquely determined by physical requirements. The methods used are shown to respect the gravitational and electromagnetic gauge invariances. In addition, a physical interpretation of the regularization method employed is offered. 相似文献
17.
Diaryl alkene alcohol 1 is a 'precipiton', a precipitating auxiliary that is used to aid the isolation of Baylis-Hillman adducts. 相似文献
18.
Sorting tags are oligomeric structures that can be used as protecting groups or chiral auxiliaries enabling solution-phase mixture syntheses of multiple tagged compounds in one pot and allowing for facile and predictable chromatographic separation of products at the end of synthetic sequences. Perfluorinated hydrocarbon and oligomeric ethylene glycol (OEG) derivatives are known classes of sorting tags. Herein we describe the preparation of OEGylated chiral oxazolidinones and their use in asymmetric solution-phase mixture aldol reactions. Through the use of such oxazolidinones based on tyrosine four different individually tagged aldol adducts were obtained as a mixture, chromatographically demixed, detagged, and it was shown that these processes gave the desired aldol products in good yield and enantioselectivity. 相似文献
19.
He X Gui J Matthews TP Williams BB Swarts SG Grinberg O Sidabras J Wilcox DE Swartz HM 《Radiation measurements》2011,46(9):882-887
Rapid and accurate retrospective dosimetry is of critical importance and strategic value for the emergency medical response to a large-scale radiological/nuclear event. One technique that has the potential for rapid and accurate dosimetry measurements is electron paramagnetic resonance (EPR) spectroscopy of relatively stable radiation-induced signals (RIS) in fingernails and toenails. Two approaches are being developed for EPR nail dosimetry. In the approach using ex vivo measurements on nail clippings, accurate estimation of the dose-dependent amplitude of the RIS is complicated by the presence of mechanically-induced signals (MIS) that are generated during the nail clipping. Recent developments in ex vivo nail dosimetry, including a thorough characterization of the MIS and an appreciation of the role of hydration and the development of effective analytic techniques, have led to improvements in the accuracy and precision of this approach. An in vivo nail dosimetry approach is also very promising, as it eliminates the problems of MIS from the clipping and it has the potential to be an effective and efficient approach for field deployment. Two types of EPR resonators are being developed for in vivo measurements of fingernails and toenails. 相似文献
20.
Efficient temperature compensation strategies for guided wave structural health monitoring 总被引:1,自引:0,他引:1
Anthony J. Croxford Jochen Moll Paul D. Wilcox Jennifer E. Michaels 《Ultrasonics》2010,50(4-5):517-528
The application of temperature compensation strategies is important when using a guided wave structural health monitoring system. It has been shown by different authors that the influence of changing environmental and operational conditions, especially temperature, limits performance. This paper quantitatively describes two different methods to compensate for the temperature effect, namely optimal baseline selection (OBS) and baseline signal stretch (BSS). The effect of temperature separation between baseline time-traces in OBS and the parameters used in the BSS method are investigated. A combined strategy that uses both OBS and BSS is considered. Theoretical results are compared, using data from two independent long-term experiments, which use predominantly A0 mode and S0 mode data respectively. These confirm that the performance of OBS and BSS quantitatively agrees with predictions and also demonstrate that the combination of OBS and BSS is a robust practical solution to temperature compensation. 相似文献