排序方式: 共有6条查询结果,搜索用时 15 毫秒
1
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.
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
3.
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
4.
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
5.
6.
Kapellios EA Karamanou S Sardis MF Aivaliotis M Economou A Pergantis SA 《Analytical and bioanalytical chemistry》2011,399(7):2421-2433
The determination of protein assembly size and relative molecular mass is currently of great importance in biochemical analysis.
In particular, the technique of nanoelectrospray (nES) with a gas-phase electrophoretic mobility molecular analyzer (GEMMA)
has received increased attention for such measurements. However, in order for the GEMMA technique to gain broader acceptance
in protein analysis, it must be further evaluated and compared with other established bioanalytical techniques. In the present
study, nES-GEMMA was evaluated for the analysis of a set of protein and protein complexes involved in the Sec and the bacterial
type III secretion pathway of enteropathogenic Escherichia coli bacteria. The same set of proteins, isolated and purified using standard biochemical protocols, were also analyzed using
multi-angle laser light scattering (MALLS) and quasi-elastic light scattering (QELS), following size exclusion chromatography.
This allowed for direct comparisons between the three techniques. It was found that nES-GEMMA, in comparison to the more established
MALLS and QELS techniques, offers several complementary advantages. It requires considerably less amount of material, i.e.,
nanogram vs. milligram amounts, and time per sample analysis, i.e., few minutes vs. tens of minutes. Whereas the determined
size and relative molecular mass are similar between the compared methods, the electrophoretic diameters determined using
nES-GEMMA seem to be systematically smaller compared to the hydrodynamic diameter derived by QELS. Some of the GEMMA technique
disadvantages include its narrow dynamic range, limited by the fact that at elevated protein concentrations there is increased
potential for the occurrence of nES-induced oligomers. Thus, it is preferred to analyze dilute protein solutions because non-specific
oligomers are less likely to occur whereas biospecific oligomers remain detected. To further understand the formation of nES-oligomers,
the effect of buffer concentration on their formation was evaluated. Also, nES-GEMMA is not compatible with all the buffers
commonly used with MALLS and QELS. Overall, however, the nES-GEMMA technique shows promise as a high-throughput proteomics/protein
structure tool. 相似文献
1