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1.
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
2.
We introduce the concept of κ-analytic and κ-Luzin spaces as images of complete metric spaces by (disjoint) upper semi-continuous compact-valued correspondences which “preserve discreteness” in some sence (Definition in Section 3.1). The case κ = ω coincides with (Lindelöf) analytic spaces studied by Choquet, the first author and others. The main results are characterizations of uniform analytic spaces in terms of other parametrizations, complete sequences of covers, and Suslin subsets of some product of a compact and a complete metric space (Theorems in Section 3.2 and in Section 4), and characterizations of topological analytic spaces as Suslin subsets of paracompact ?ech-complete spaces (Theorem in Section 5). 相似文献
3.
Lattice models (on a hypercubic lattice of dimension larger than or equal to three) with spins attaining a finite number of values and finite-range interactions at low temperatures are considered. The existence of rigid interfaces as well as of surface tension under appropriate conditions is proven and the properties of corresponding Gibbs states are investigated. 相似文献
4.
Abstract Many solar UV measurements, either terrestrial or personal, weight the raw data by the erythemal action spectrum. However, a problem arises when one tries to estimate the benefit of vitamin D(3) production based on erythemally weighted outdoor doses, like those measured by calibrated R-B meters or polysulphone badges, because the differences between action spectra give dissimilar values. While both action spectra peak in the UVB region, the erythemal action spectrum continues throughout the UVA region while the previtamin D(3) action spectrum stops near that boundary. When one uses the previtamin D(3) action spectrum to weight the solar spectra (D(eff)), one gets a different contribution in W m(-2) than what the erythemally weighted data predicts (E(eff)). Thus, to do proper benefit assessments, one must incorporate action spectrum conversion factors (ASCF) into the calculations to change erythemally weighted to previtamin D(3)-weighted doses. To date, all benefit assessments for vitamin D(3) production in human skin from outdoor exposures are overestimates because they did not account for the different contributions of each action spectrum with changing solar zenith angle and ozone and they did not account for body geometry. Here we describe how to normalize the ratios of the effective irradiances (D(eff)/E(eff)) to get ASCF that change erythemally weighted to previtamin D(3)-weighted doses. We also give the ASCF for each season of the year in the northern hemisphere every 5 degrees from 30 degrees N to 60 degrees N, based on ozone values. These ASCF, along with geometry conversion factors and other information, can give better vitamin D(3) estimates from erythemally weighted outdoor doses. 相似文献
5.
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
6.
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
7.
8.
D. Preiss proved that the graph of the derivative of a continuous Gateaux-differentiable function f : ℝ2 → ℝ is always connected. We show that this is no longer true in higher dimensions: we construct a continuous, Gateaux-differentiable
function f : ℝ3 → ℝ for which the range of its gradient mapping {∇ f(x) : x ∈ ℝ3} is disconnected. We also give an example of an approximately differentiable continuous function on ℝ2 such that the range of its gradient mapping is disconnected.
The work is a part of the research project MSM 0021620839 financed by MSMT and it was also partly supported by GAČR 201/06/0198
and GAČR 201/06/0018. 相似文献
9.
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
10.