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Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total
reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first
derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by
channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and
reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It
becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width
and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial
for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling
only occurs in a finite range of ɛ. 相似文献
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Abid OU Nawaz M Ibad MF Khera RA Iaroshenko V Langer P 《Organic & biomolecular chemistry》2011,9(7):2185-2191
Aryl-substituted pyridines and pyrimidines were prepared by [4+2] cycloadditions of alkynyl-substituted pyridines and -pyrimidines with electron-rich dienes. The reactions proceed by formation of a bridged cycloadduct and subsequent thermal extrusion of ethylene. The pyridine moiety plays a crucial role for the success of the reaction. 相似文献
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MF Miller IA Franchi AS Sexton CT Pillinger 《Rapid communications in mass spectrometry : RCM》1999,13(13):1211-1217
The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Obaid-ur-Rahman Abid Muhammad Farooq Ibad Asad Ali Nasim Hasan Rama Peter Langer 《Tetrahedron letters》2010,51(12):1541-721
The palladium(0)-catalyzed Suzuki cross-coupling reaction of the bis(triflates) of phenyl 1,4-dihydroxy-2-naphthoate afforded various 1,4-diaryl-2-naphthoates. The reactions proceeded with very good site-selectivity. Due to electronic reasons, the first attack occurred at the sterically more hindered position C-1. 相似文献
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The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.
This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life. 相似文献
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Ibad MF Abid OU Adeel M Nawaz M Wolf V Villinger A Langer P 《The Journal of organic chemistry》2010,75(23):8315-8318
The Me(3)SiOTf-mediated condensation of 1-ethoxy-2-fluoro-1,3-bis(trimethylsilyloxy) 1,3-dienes with 3-cyanochromones afforded 3-cyano-2-(4-ethoxy-3-fluoro-2,4-dioxobutyl)chroman-4-ones. Their reaction with triethylamine afforded fluorinated azaxanthones or biaryls. The product distribution depends on the structure of the diene. The formation of the biaryls can be explained by an unprecedented domino "retro-Michael/aldol/fragmentation" reaction. 相似文献
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Ibad MF Langer P Schulz A Villinger A 《Journal of the American Chemical Society》2011,133(51):21016-21027
The solvent-coordinated [Me(3)Si·arene][B(C(6)F(5))(4)] salts (arene = benzene, toluene, ethylbenzene, n-propylbenzene, isopropylbenzene, o-xylene, m-xylene, p-xylene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene) are prepared and fully characterized. As an interesting decomposition product the formation of bissilylated fluoronium ion [Me(3)Si-F-SiMe(3)](+) was observed and even cocrystallized with [Me(3)Si·arene][B(C(6)F(5))(4)] (arene = benzene and toluene). Investigation of the degradation of [Me(3)Si·arene][B(C(6)F(5))(4)] reveals the formation of fluoronium salt [Me(3)Si-F-SiMe(3)][B(C(6)F(5))(4)], B(C(6)F(5))(3), and a reactive "C(6)F(4)" species which could be trapped with CS(2). Upon addition of CS(2), the formation of a formal S-heterocyclic carbene adduct, C(6)F(4)CS(2)-B(C(6)F(5))(3), was observed. The structure and bonding of substituted [Me(3)Si·arene][B(C(6)F(5))(4)] with arene = R(n)C(6)H(6-n) (R = H, Me, Et, Pr, and Bu; n = 0-6) is discussed on the basis of experimental and theoretical data. X-ray data of [Me(3)Si·arene][B(C(6)F(5))(4)] salts reveal nonplanar arene species with significant cation···anion interactions. As shown by different theoretical approaches (charge transfer, partial charges, trimethylsilyl affinity values) stabilizing inductive effects occur; however, the magnitude of such effects differs depending on the degree of substitution and the substitution pattern. 相似文献
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Ihsan Ullah Muhammad Sher Rasheed Ahmad Khera Muhammad Farooq Ibad Christine Fischer 《Tetrahedron》2010,66(10):1874-1884
The [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with 1-hydroxy-5-silyloxy-hex-4-en-3-ones resulted in the one-pot formation of 3-aryl-3,4-dihydroisocoumarins. The reactions proceeded by regioselective cyclization to give 6-(2-aryl-2-chloroethyl)salicylates, which underwent a silica gel-mediated lactonization. The cyclizations of protected 1-amino-5-silyloxy-hex-4-en-3-ones proved to be not regioselective. 相似文献
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