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61.
Vladimir Martis Martin Martis John Lipp Dirk Detollenaere Trevor Rayment Gopinathan Sankar Wim Bras 《Journal of synchrotron radiation》2014,21(4):744-750
Energy‐resolved electron‐yield X‐ray absorption spectroscopy is a promising technique for probing the near‐surface structure of nanomaterials because of its ability to discriminate between the near‐surface and bulk of materials. So far, the technique has only been used in model systems. Here, the local structural characterization of nanoporous cobalt‐substituted aluminophosphates is reported and it is shown that the technique can be employed for the study of open‐framework catalytically active systems. Evidence that the cobalt ions on the surface of the crystals react differently to those in the bulk is found. 相似文献
62.
ABSTRACTNew fluorene-containing copolymer was prepared via the catalytic dehydrocoupling reaction of 9,9-dipropargylfluorene and 4,4′-diphenyl-2,6-dibromo-dithieno-[3,2-b:2′,3′-d]silole in 44% yield. The resulting polymer was completely soluble in common organic solvents. The thermal behaviors and optical properties of the resulting polymer were measured and discussed. The chemical structure of polymer was characterized by NMR, IR, and UV-visible spectroscopies. The polymer showed characteristic wide UV-visible absorption band and blue PL maximum value at 440 nm, which is corresponding photon energy of 2.82 eV. The quantum yield (6.44%) of poly(DPF-DTS) was found to be 5 times higher than that of poly(DPF-bithiophene)). 相似文献
63.
As one of the biological endogenous pigments, biliverdin (BV) and its dimethyl ester (BVE) have extremely weak fluorescence in solution with quantum yield less than 0.01%. However, the situation reverses with the addition of zinc ions. The strength for fluorescence of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex is greatly enhanced and fluorescence quantum yield can increase to \begin{document}$ \sim $\end{document} 5%. Herein, we studied ultrafast excited state dynamics of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in ethanol, \begin{document}$ n $\end{document} -propanol, and DMSO solutions in order to reveal the mechanism of fluorescence quantum yield enhancement. The results show that BVE can form a stable coordination complex with zinc with 1:1 stoichiometry in solution. BVE is structurally and energetically more stable in the complex. Using picosecond time-resolve fluorescence and femtosecond transient absorption spectroscopy, we show that smaller non-radiative rate constant of BVE-Zn\begin{document}$ ^{2+} $\end{document} complex in DMSO is the key to increasing its fluorescence quantum yield and the excited state decay mechanism is also revealed. These results provide valuable information about the fluorescence property change after BVE binding to metal ions and may provide a guidance for the study of phytochromes or other fluorescence proteins in which BV/BVE acts as chromophores. 相似文献
64.
Residence time spectra and material distributions in an operating caprolactam production plant were measured by means of sodium 24, bromine 82 and technetium 99m. The results of the tracerexperiments contributed to an optimization of the plant. 相似文献
65.
《Biomedical chromatography : BMC》2017,31(8)
The present study was designed to determine the fatty acid composition and phytosterol contents of Turkish native olive cultivars, namely Kilis Yağlık and Nizip Yağlık cv. In this context, olive fruits from 34 locations were sampled and then screened for their components in comparison. Fifteen different fatty acids were found in both olive oils. In the order of abundance, the most important ones were oleic acid (18:1) > palmitic acid (16:0) > linoleic acid (18:2) > stearic acid (18:0). Significant differences were observed in the contents of oleic acid (18:1), palmitic acid (16:0), linoleic acid (18:2) but not for stearic acid content in comparison both oils (p < 0.01). There were significant differences in terms of unsaturated fatty acids, saturated fatty acids and polyunsaturated fatty acids (p < 0.01). The seven phytosterols – cholesterol, campesterol, stigmasterol, β ‐sitosterol, Δ‐5‐avenasterol, Δ‐7‐stigmastenol and Δ‐7‐avenasterol – were studied in both oil sources. The predominant sterols were β ‐sitosterol, Δ5‐avenasterol and campesterol in the samples analysed. However, no significant differences were found in the levels of the phytosterols between the two olive cultivars. 相似文献
66.
Useful yield for electrospray droplet impact/secondary ion mass spectrometry was estimated. The mixtures of C60/rhodamine B and C60/Aerosol OT were used as the samples for the positive and negative mode of operations, respectively. By assuming that (i) the desorption efficiencies are about the same for C60, rhodamine B and Aerosol OT, and (ii) desorption of ionic compounds directly gives the secondary ion signals, the useful yields (i.e. total ions generated divided by the total molecules desorbed) for C60 were estimated to be ~0.1. This value should be regarded as the upper limit because the neutralization of positive and negative ions in the plume and desorption of ionic compounds as neutral species are not taken into account. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
The oxidative coupling of methane over La 2 O 3 /CaO type-catalyst in a fixed-bed reactor is studied under a wide range of operating conditions(973相似文献
68.
69.
Wei Zhou Xiangning Fang Qinglong Qiao Wenchao Jiang Yue Zhang Zhaochao Xu 《中国化学快报》2021,32(2):943-946
With the development of single-molecule detection and super-resolution fluorescence imaging, rhodamine dyes gain new life. Through the modification of the N-substituents and the replacement of the oxygen atom in xanthene, the wavelength and brightness can be effectively changed. However, the spectra of rhodamine, especially due to the balance between ring-closed non-fluorescent lactone and ring-opened fluorescent zwitterion/cation, are sensitive to interference from various environmental factors. In this way, the spectral data of various rhodamines reported by different research groups under different test conditions lacked comparability, sometimes even lacked accuracy. In order to meet the requirements for the accuracy and uniformity of spectral data in the research of single molecule imaging and dye structure-fluorescence relationship study, we have tested the spectra of fifteen rhodamine dyes that cover the visible and near-infrared regions under exactly the same conditions. By studying the dependence of the spectra on dye concentrations, it was confirmed that 1 μmol/L was ideal for detection less from the interference of dye molecule aggregation. We provide comprehensive and reliable spectral data of these fifteen dyes, which are expected to be used as references for future research. And the direct comparison of different rhodamine spectra would help to understand the structure-fluorescence relationship of rhodamines. 相似文献
70.
Andrea Giuntoli Nicola Calonaci Sebastiano Bernini Dino Leporini 《Journal of Polymer Science.Polymer Physics》2017,55(23):1760-1769
The relation between elasticity and yielding is investigated in a model polymer solid by Molecular‐Dynamics simulations. By changing the bending stiffness of the chain and the bond length, semicrystalline and disordered glassy polymers — both with bond disorder — as well as nematic glassy polymers with bond ordering are obtained. It is found that in systems with bond disorder the ratio τY/G between the shear yield strength τY and the shear modulus G is close to the universal value of the atomic metallic glasses. The increase of the local nematic order in glasses leads to the increase of the shear modulus and the decrease of the shear yield strength, as observed in experiments on nematic thermosets. A tentative explanation of the subsequent reduction of the ratio τY/G in terms of the distributions of the per‐monomer stress is offered. © 2017 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2017 , 55, 1760–1769 相似文献