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- Kristensson, Elias, et al.
(författare)
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Physical explanation of the SLIPI technique by the large scatterer approximation of the RTE
- 2017
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Ingår i: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 189, s. 112-125
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Tidskriftsartikel (refereegranskat)abstract
- Visualizing the interior of a turbid scattering media by means light-based methods is not a straightforward task because of multiple light scattering, which generates image blur. To overcome this issue, a technique called Structured Laser Illumination Planar Imaging (SLIPI) was developed within the field of spray imaging. The method is based on a ‘light coding’ strategy to distinguish between directly and multiply scattered light, allowing the intensity from the latter to be suppressed by means of data post-processing. Recently, the performance of the SLIPI technique was investigated, during which deviations from theoretical predictions were discovered. In this paper, we aim to explain the origin of these deviations, and to achieve this end, we have performed several SLIPI measurements under well-controlled conditions. Our experimental results are compared with a theoretical model that is based on the large scatter approximation of the Radiative Transfer Equation but modified according to certain constraints. Specifically, our model is designed to (1) ignore all off-axis intensity contributions, (2) to treat unperturbed- and forward-scattered light equally and (3) to accept light to scatter within a narrow forward-cone as we believe these to the rules governing the SLIPI technique. The comparison conclusively shows that optical measurements based on scattering and/or attenuation in turbid media can be subject to significant errors if not all aspects of light-matter interactions are considered. Our results indicate, as were expected, that forward-scattering can lead to deviations between experiments and theoretical predictions, especially when probing relatively large particles. Yet the model also suggests that the spatial frequency of the superimposed ‘light code’ as well as the spreading of the light-probe are important factors one also needs to consider. The observed deviations from theoretical predictions could, however, potentially be exploited to assess particle size
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- Engström, Christian, et al.
(författare)
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Homogenization of the Maxwell equations using Floquet-Bloch decomposition
- 2003
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Ingår i: Mathematical and numerical waves 2003. - Berlin, Heidelberg : Springer. - 9783642558566 - 354040127X ; , s. 412-416
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Konferensbidrag (refereegranskat)abstract
- Using Bloch waves to represent the full solution of the Maxwell equations inperiodic media, we study the limit process where the material's period becomes much smaller than the wavelenght. it is seen that effective material parameters can be extracted and explicity represented in terms of the non-vanishing Bloch waves, providing an alternative means of homogenization.
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- Mayer, Ludovic, et al.
(författare)
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Widespread Pesticide Distribution in the European Atmosphere Questions their Degradability in Air
- 2024
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Ingår i: Environmental Science and Technology. - 0013-936X. ; 58:7, s. 3342-3352
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Tidskriftsartikel (refereegranskat)abstract
- Risk assessment of pesticide impacts on remote ecosystems makes use of model-estimated degradation in air. Recent studies suggest these degradation rates to be overestimated, questioning current pesticide regulation. Here, we investigated the concentrations of 76 pesticides in Europe at 29 rural, coastal, mountain, and polar sites during the agricultural application season. Overall, 58 pesticides were observed in the European atmosphere. Low spatial variation of 7 pesticides suggests continental-scale atmospheric dispersal. Based on concentrations in free tropospheric air and at Arctic sites, 22 pesticides were identified to be prone to long-range atmospheric transport, which included 15 substances approved for agricultural use in Europe and 7 banned ones. Comparison between concentrations at remote sites and those found at pesticide source areas suggests long atmospheric lifetimes of atrazine, cyprodinil, spiroxamine, tebuconazole, terbuthylazine, and thiacloprid. In general, our findings suggest that atmospheric transport and persistence of pesticides have been underestimated and that their risk assessment needs to be improved.
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- Tyler, Torbjörn, et al.
(författare)
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Nu startar projekt Skånes Mossor!
- 2007
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Ingår i: Myrinia. - 1102-4194. ; 17:1, s. 52-57
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 7. |
- Tyler, Torbjörn, et al.
(författare)
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Nu startar projekt Skånes Mossor!
- 2007
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Ingår i: Botaniska Notiser. - 0006-8195. ; 140:2, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- The Lund Botanical Society 2007-03-23 decided to launch a project with the following aims: 1) to map the frequency and distribution of all bryophytes in the province of Skåne, southernmost Sweden, thereby making way for future studies of changes in the flora, 2) to find and document as many sites as possible for nationally and regionally rare or endangered bryophytes and initiate conservation actions at these sites, 3) to increase our knowledge of the ecological demands of individual taxa, and 4) to enhance the level of knowledge concerning bryophytes among both amateur botanists and professional nature conservationists. The province has been divided into 534 5 x 5 km grid-squares. The central square kilometre within each grid-square will be surveyed and the result used for unbiased estimates of the frequency of each taxon. In addition, within each grid-square, a variable number of special areas which may be presumed to have a rich or unusual bryophyte flora have been preselected for the survey. Additional areas may be selected by the recorders themselves, but the ultimate goal is not to survey the grid-square as a whole. A special determination key and nomenclatural check-list to all 658 taxa hithereto known from the province, as well as various instructions and forms for the volonteer recorders, have been made available on the Internet and a central database with an Internet interface is under way. Various kinds of courses have been initiated with the aim of educating future recorders. The aim is to survey all grid-squares during a 20 year period and the project is now calling for support from bryologists world-wide.
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- Gower, Artur, et al.
(författare)
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Effective Waves for Random Three-dimensional Particulate Materials
- 2020
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- How do you take a reliable measurement of a material whose microstructure is random? When using wave scattering, the answer is often to take an ensemble average (average over time or space). By ensemble averaging we can calculate the average scattered wave and the effective wavenumber. To date, the literature has focused on calculating the effective wavenumber for a plate filled with particles. One clear unanswered question was how to extend this approach to a material of any geometry and for any source. For example, does the effective wavenumber depend on only the microstructure, or also on the material geometry? In this work, we demonstrate that the effective wavenumbers depend on only microstructure and not the geometry, though beyond the long wavelength limit there are multiple effective wavenumbers. We show how to calculate the average wave scattered from a random particulate material of any shape, and for broad frequency ranges. As an example, we show how to calculate the average wave scattered from a sphere filled with particles.
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| 9. |
- Gower, Artur, et al.
(författare)
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Effective waves for random three-dimensional particulate materials
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- How do you take a reliable measurement of a material whose microstructure is random? When using wave scattering, the answer is often to take an ensemble average (average over time or space). By ensemble averaging we can calculate the average scattered wave and the effective wavenumber. To date, the literature has focused on calculating the effective wavenumber for a plate filled with particles. One clear unanswered question was how to extend this approach to a material of any geometry and for any source. For example, does the effective wavenumber depend on only the microstructure, or also on the material geometry? In this work, we demonstrate that the effective wavenumbers depend on only microstructure, though beyond the long wavelength limit there are multiple effective wavenumbers for one fixed incident frequency. We show how to calculate the average wave scattered from a random particulate material of any shape, and for broad frequency ranges. As an example, we show how to calculate the average wave scattered from a sphere filled with particles.
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