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- Johansson, Sara, et al.
(författare)
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An alternative methodology for the analysis of electrical resistivity data from a soil gas study
- 2011
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Ingår i: Geophysical Journal International. - 0956-540X. ; 186:2, s. 632-640
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to present an alternative method for the analysis of resistivity data. The methodology was developed during a study to evaluate if electrical resistivity can be used as a tool for analysing subsurface gas dynamics and gas emissions from landfills. The main assumption of this study was that variations in time of resistivity data correspond to variations in the relative amount of gas and water in the soil pores. Field measurements of electrical resistivity, static chamber gas flux and weather data were collected at a landfill in Helsingborg, Sweden. The resistivity survey arrangement consisted of nine lines each with 21 electrodes in an investigation area of 16 x20 m. The ABEM Lund Imaging System provided vertical and horizontal resistivity profiles every second hour. The data were inverted in Res3Dinv using L-1-norm-based optimization method with a standard least-squares formulation. Each horizontal soil layer was then represented as a linear interpolated raster model. Different areas underneath the gas flux measurement points were defined in the resistivity model of the uppermost soil layer, and the vertical extension of the zones could be followed at greater depths in deeper layer models. The average resistivity values of the defined areas were calculated and plotted on a time axis, to provide graphs of the variation in resistivity with time in a specific section of the ground. Residual variation of resistivity was calculated by subtracting the resistivity variations caused by the diurnal temperature variations from the measured resistivity data. The resulting residual resistivity graphs were compared with field data of soil moisture, precipitation, soil temperature and methane flux. The results of the study were qualitative, but promising indications of relationships between electrical resistivity and variations in the relative amount of gas and water in the soil pores were found. Even though more research and better data quality is necessary for verification of the results presented here, we conclude that this alternative methodology of working with resistivity data seems to be a valuable and flexible tool for this application.
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| 3. |
- Rosqvist, Fredrik, 1985-, et al.
(författare)
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Fatty acids in multiple circulating lipid fractions reflects the composition of liver triglycerides in humans
- 2022
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Ingår i: Clinical Nutrition. - : Elsevier BV. - 1532-1983 .- 0261-5614. ; 41:4, s. 805-809
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims: Fatty acids (e.g. 16:1n-7) and desaturase indices (e.g. stearoyl-CoA desaturase, SCD) in plasma cholesteryl esters (CE) and phospholipids (PL) are used as biomarkers of dietary fat quality and lipid metabolism and are associated with disease outcomes. Endogenously produced circulating fatty acids are believed to reflect composition of the liver, yet little data exist to support such relationship. We investigated associations between circulating fatty acids and fatty acids within the liver. Methods: Liver biopsies and blood were collected from n = 60 patients with non-alcoholic fatty liver disease. Fatty acids in CE, PL and triglycerides (TG) in plasma and liver were analyzed using gas chromatography. Associations were assessed using Spearman rank correlations. Results: Overall, fatty acids and desaturase indices in plasma PL and TG showed moderate–strong correlations with fatty acids and desaturase indices in corresponding lipid fractions in liver. For plasma CE, 16:1n-7 and SCD were correlated with 16:1n-7 and SCD in liver CE. Noteworthy, fatty acids in plasma CE and PL also showed moderate–strong correlations with fatty acids in liver TG (e.g. r = 0.82–0.87 for 16:1n-7 and r = 0.77 for SCD). Conclusion: We demonstrate that fatty acids in circulating lipid fractions, including CE, TG and PL, reflects the composition of liver TG in humans, suggesting that circulating fatty acids might be useful biomarkers for the fatty acid composition of the liver. As liver tissue is rarely available in cohort studies, our findings could enhance our understanding of plasma fatty acids as markers of hepatic lipid metabolism and their links to metabolic diseases.
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| 4. |
- Rosqvist, Hakan, et al.
(författare)
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Geoelectrical imaging for detection of water migration in a bioreactor landfill
- 2010
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Ingår i: Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP. - 9781617384172 ; 1, s. 361-368
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Konferensbidrag (refereegranskat)abstract
- In this paper we describe field investigations of leachate recirculation at a bioreactor landfill using geoelectrical imagining technique (i.e., electrical resistivity) combined with a tracer test. The use of geoelectrical imagining techniques is an established practice for environmental investigations and monitoring of various landfill processes and in recent years also the bioreactor landfill concept has been emphasised. In the study, the electrical resistivity technique was evaluated and the possibility to detect water and gas migration in the waste mass was investigated. Results showing moisture migration through the bioreactor landfill, during leachate flushing and during a tracer test, are presented. Also results indicating the resistivity technique being useful for biogas detection are shown.
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