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- Bower, K. N., et al.
(author)
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The Great Dun Fell experiment 1995 : An overview
- 1999
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In: Atmospheric Research. - 0169-8095. ; 50:3-4, s. 151-184
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Journal article (peer-reviewed)abstract
- During March and April of 1995 a major international field project was conducted at the UMIST field station site on Great Dun Fell in Cumbria, Northern England. The hill cap cloud which frequently envelopes this site was used as a natural flow through reactor to examine the sensitivity of the cloud microphysics to the aerosol entering the cloud and also to investigate the effects of the cloud in changing the aerosol size distribution, chemical composition and associated optical properties. To investigate these processes, detailed measurements of the cloud water chemistry (including the chemistry of sulphur compounds, organic and inorganic oxidised nitrogen and ammonia), cloud microphysics and properties of the aerosol and trace gas concentrations upwind and downwind of the cap cloud were undertaken. It was found that the cloud droplet number was generally strongly correlated to aerosol number concentration, with up to 2000 activated droplets cm-3 being observed in the most polluted conditions. In such conditions it was inferred that hygroscopic organic compounds were important in the activation process. Often, the size distribution of the aerosol was substantially modified by the cloud processing, largely due to the aqueous phase oxidation of S(IV) to sulphate by hydrogen peroxide, but also through the uptake and fixing of gas phase nitric acid as nitrate, increasing the calculated optical scattering of the aerosol substantially (by up to 24%). New particle formation was also observed in the ultrafine aerosol mode (at about 5 nm) downwind of the cap cloud, particularly in conditions of low total aerosol surface area and in the presence of ammonia and HCl gases. This was seen to occur at night as well as during the day via a mechanism which is not yet understood. The implications of these results for parameterising aerosol growth in Global Climate Models are explored.
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| 4. |
- Jarlman, O, et al.
(author)
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Laser transillumination of breast tissue phantoms using time-resolved techniques
- 1996
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In: European Radiology. - 0938-7994. ; 6:3, s. 387-392
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Journal article (peer-reviewed)abstract
- The objective of this study was to evaluate a pulsed laser transillumination technique based on time-resolved detection on breast-tissue-like phantoms. Experiments have been performed on tissue-like plastic phantoms with different scattering characteristics. The effects of time-gate width, size, localisation and refractive index of hidden objects have been scrutinised. Our study showed that the shorter the time-gate the higher the contrast. The contrast is very dependent of the size of the hole, whereas the full width half maximum is not. Furthermore, the investigation showed that the changes of early detected light in an experimental setting is due to scattering, adn not to a higher speed of the transmitted light.
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| 5. |
- Jarlman, O, et al.
(author)
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Time-resolved white light transillumination for optical imaging
- 1997
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In: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 38:1, s. 185-189
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Journal article (peer-reviewed)abstract
- Purpose: To describe a new breast-imaging method with the potential of multi-spectral optical transillumination based on a time-resolved technique. Material and Methods: A breast phantom was irradiated with ultra-short laser pulses of white light generated by self-phase modulation of an incident high-power laser pulse in water. Time-resolved detection of the transmitted light was performed. Contrast resolution was studied using different absorbers located inside the breast phantom. Results and Conclusion: The results showed that simultaneous, multi-spectral transillumination is possible. The technique can also be used for measurements of optical properties in tissue.
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