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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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Hoepker AC Gupta L Ma Y Faggin MF Collum DB 《Journal of the American Chemical Society》2011,133(18):7135-7151
Ortholithiation of 1-chloro-3-(trifluoromethyl)benzene with lithium diisopropylamide (LDA) in tetrahydrofuran at -78 °C displays characteristics of reactions in which aggregation events are rate limiting. Metalation with lithium-chloride-free LDA involves a rate-limiting deaggregation via dimer-based transition structures. The post-rate-limiting proton transfers are suggested to involve highly solvated triple ions. Autocatalysis by the resulting aryllithiums or catalysis by traces (<100 ppm) of LiCl diverts the reaction through di- and trisolvated monomer-based pathways for metalation at the 2 and 6 positions, respectively. The regiochemistry is dictated by a combination of kinetically controlled metalations overlaid by an equilibration involving diisopropylamine that is shown to occur by the microscopic reverse of the monomer-based metalations. 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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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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Faggin MF Green SK Clark IT Queeney KT Hines MA 《Journal of the American Chemical Society》2006,128(35):11455-11462
The etching of Si(100) surfaces in ultrapure water was studied with a combination of infrared spectroscopy (FTIR) and scanning tunneling microscopy (STM). While the FTIR results show that the initially rough H/Si(100) surface becomes highly homogeneous during etching, a phenomenon generally associated with surface smoothing, STM images reveal that the homogeneity is associated with the formation of well-defined etch hillocks. After many hours of etching, the resulting H-terminated surface is composed of stripes of atomically flat Si(100) terminated by etch hillocks bounded by {111}- and {110}-oriented microfacets. Polarization analysis of the Si-H stretching modes provides strong evidence for uniform dihydride-termination of the flat regions, with the narrow (approximately 25 A) width of these stripes allowing for relaxation of steric strain between neighboring dihydrides. The unusual hill-and-valley etch morphology is attributed to the effects of steric strain on the reactivity of sites on the etched surface. 相似文献
8.
Ma Y Hoepker AC Gupta L Faggin MF Collum DB 《Journal of the American Chemical Society》2010,132(44):15610-15623
Lithium diisopropylamide (LDA) in tetrahydrofuran at -78 °C undergoes 1,4-addition to an unsaturated ester via a rate-limiting deaggregation of LDA dimer followed by a post-rate-limiting reaction with the substrate. Muted autocatalysis is traced to a lithium enolate-mediated deaggregation of the LDA dimer and the intervention of LDA-lithium enolate mixed aggregates displaying higher reactivities than LDA. Striking accelerations are elicited by <1.0 mol % LiCl. Rate and mechanistic studies have revealed that the uncatalyzed and catalyzed pathways funnel through a common monosolvated-monomer-based intermediate. Four distinct classes of mixed aggregation effects are discussed. 相似文献
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