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A study of the fluorescence spectra of fly ash samples from different sources has shown that each samples has a characteristic fluorescence and excitation spectrum which could be used to identify and monitor its presence. Fluorescence lifetime studies of samples from different sources have demonstrated characteristic features which can be used for identification. The fluorescence method should be useful for in situ and remote monitoring applications. 相似文献
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Cumulant functions are introduced to describe the statistical state of a radiation field. These functions are simply related
to the optical coherence functions but have some interesting features. It is shown that if the cumulant functions of all orders
greater than some numberN
0 vanish then they also vanish for all orders greater than 2. Thermal field is the only field having this property. This property
holds whether the field is described by a classical stochastic process or by a quantum density operator. Further the particular
operator ordering used in defining these cumulant functions for the quantized field affects only the second order cumulant
function. To describe the statistical state of a vector field such as partially polarized or unpolarized radiation, one would
need to introduce cumulant tensors. 相似文献
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A. J. Berlinsky F. Wudl K. C. Lim C. R. Fincher A. J. Heeger 《Journal of Polymer Science.Polymer Physics》1984,22(5):847-852
A theory is proposed for the rod to coil transition in polydiacetylene 4BCMU and related polymers which is based on the hypothesis that the high-temperature (yellow) phase consists predominantly of the cis structure, while the low-temperature (red) phase is trans. Because the occurrence of a cis-trans interface is energetically costly, the correlation length for either isomer remains long and the transition is sharp, much like the helix-coil transition in the theory of Zimm and Bragg. The transition is driven by the higher entropy of the cis isomer, which is free to coil, unlike the trans or butatriene forms. The theory gives excellent agreement with optical absorption measurements and is consistent with all other experimental data for this system. 相似文献
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C.R. Fincher D.L. Peebles A.J. Heeger M.A. Druy Y. Matsumura A.G. MacDiarmid H. Shirakawa S. Ikeda 《Solid State Communications》1978,27(5):489-494
Optical absorption and reflection measurements have been carried out on pure and doped polyacetylene films. The absorption data are consistent with a model of (CH)X as a direct gap quasi-l d semiconductor; doping with AsF5 or iodine introduces absorption within the gap, but appears to leave the interband transition intact. The anisotropic reflectance from partially aligned films and the increased optical anisotropy upon doping provide evidence of quasi-l d behavior of the semiconducting pure polymer and the metallic doped polymer. 相似文献
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J. A. Gelbwachs M. Birnbaum A. W. Tucker C. L. Fincher 《Optical and Quantum Electronics》1972,4(2):155-160
The concentrations of nitrogen dioxide (NO2) in the atmosphere have been determined in real time and with a sensitivity of one part per billion. Laser excitation of NO2 was at 4416 and 4880 Å and fluorescence was monitored at 0.7 to 0.8 m. Results obtained on typical smoggy days in Los Angeles are presented. 相似文献
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Curtis R. Fincher Jr 《Molecular Crystals and Liquid Crystals》2013,570(1):559-570
In most liquid crystal polymers when a thin sample is sheared the polymer exhibits a periodic pattern or texture. While this phenomena has been widely noted, a complete and satisfactory explanation is not yet in hand. We present the results of a study of the dynamics of the formation of the banded texture in liquid crystalline polymers after shear. The data were collected by the diffraction of light from the texture. This approach directly provides the key parameters to characterize the texture without the ambiguity that is often involved with microscopy. It was found that the overall nature of the modulation that gives rise to the texture appears to not vary with time except in magnitude. Both thewavelength and the coherence length of the modulation remain fixed. While both shear rate and thickness of the sample have little effect upon the texture, concentration of the polymer has a very large effect. 相似文献
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MA Freitas CL Hendrickson AG Marshall 《Rapid communications in mass spectrometry : RCM》1999,13(15):1639-1642
We present a novel approach for the determination of activation energy for the unimolecular dissociation of a large (>50 atoms) ion, based on measurement of the unimolecular dissociation rate constant as a function of continuous-wave CO(2) laser intensity. Following a short ( approximately 1 s) induction period, CO(2) laser irradiation produces an essentially blackbody internal energy distribution, whose 'temperature' varies inversely with laser intensity. The only currently available method for measuring such activation energies is blackbody infrared radiative dissociation (BIRD). Compared with BIRD, FRAGMENT: (a) eliminates the need to heat the surrounding ion trap and vacuum chamber to each of several temperatures (each requiring hours for temperature equilibration); (b) offers a three-fold wider range of effective blackbody temperature; and (c) extends the range of applications to include initially cold ions (e.g., gas-phase H/D exchange). Our FRAGMENT-determined activation energy for dissociation of protonated bradykinin, 1.2 +/- 0.1 eV, agrees within experimental error to the value, 1.3 +/- 0.1 eV, previously reported by Williams et al. from BIRD experiments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Fairweather JK Hrmova M Rutten SJ Fincher GB Driguez H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(11):2603-2610
Complex oligosaccharides with newly formed (1,3)-beta-glycosidic linkages were obtained in good to excellent yields when substituted or unsubstituted alpha-laminaribiosyl fluorides, acting as donors, were condensed onto mono- and disaccharide beta-D-hexopyranoside acceptors by using a (1,3)-beta-D-glycosynthase. These linear and branched (1,3)-beta-linked oligosaccharides could prove to be important in a range of medical, pharmaceutical, and agricultural applications. Furthermore, the observation that the (1,3)-beta-D-glucan glycosynthase accommodates (1,3)-, (1,4),- and (1,6)-beta-oligosaccharides in its acceptor subsites suggests novel, yet unexpected physiological roles for the wild type (1,3)-beta-D-glucan endohydrolase from higher plants. 相似文献
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