| 11. |
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| 12. |
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| 13. |
- Persson, Andreas, et al.
(författare)
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Evaluation of an optical sensor for tuber yield monitoring
- 2004
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Ingår i: Transactions of the Asae. - 0001-2351. ; 47:5, s. 1851-1856
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Tidskriftsartikel (refereegranskat)abstract
- A sensor for monitoring the yield of tubers was tested in the laboratory and in the field. The laboratory test was designed to investigate whether the sensor varied in its measurements of tuber size, whether the recorded size differed within the width of the sensor, and whether tilting of the sensor affected the result. The test objects were spheres, and measurements were carried out on three different sizes. A statistical analysis showed how the sensor measured the sizes for the different combinations of size, position, and inclination. In the field, a harvester-mounted sensor was used to monitor yield of Bintje potatoes in terms of tuber size and weight. The results obtained were compared with those from mechanical load-cell measurements. An expression relating tuber size to weight was determined. Plot-harvesting tubers provided data for evaluation of tuber size in relation to yield. The results showed that the errors in size determination by the sensor were in the order of 1% to 2%. Different size classes were well differentiated. Some differences were noted for object position and sensor inclination. Field tests showed that the mean deviation from measured weight was about 1%. It was concluded that sensor errors were small and that the sensor could discriminate between different sizes for the spheres used in the study. In the field, the sensor worked with good consistency and is a potential option for tuber yield monitoring.
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| 14. |
- Persson, Andreas
(författare)
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Hydrological Modelling, Topographical Influence and Yield Mapping in Precision Agriculture
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of topographical data in hydrological and agricultural applications has increased with GPS data availability and the concept of precision agriculture. This thesis investigates the relationships between topography and in one case simulated soil moisture and in the other case yield. The yield was recorded with a new optical sensor, which uses a digital camera to detect objects and records the yield on tuber level. The accuracy of this yield monitor was determined to be better than that of alternative methods. The topographical influence on yield was determined with correlation to topographical indices. A spatial regression and a multiple step-wise regression method resulted in 20% of yield being explained by elevation, gradient and a new topographical index (horizontal position) in one field. In the other field studied, 18% of the yield was explained by topography, here the horizontal position was replaced by drainage area. Drainage area (a) calculation is a derivation of digital elevation models (DEMs) used within e.g. the TWI (topographical wetness index), ln (a / tan ƒÒ). The methods to quantify (a) are several and have an influence on the result of the TWI. Three drainage area algorithms were therefore tested together with TWI to map soil moisture for one German and one Swedish site. The methods tested included an eight-directions algorithm, a ¡¥stream tube¡¦ algorithm and a form-based algorithm. In the correlation with soil moisture the stream-tube and form-based methods performed best. Conventional drainage area calculations are applied to surfaces without any of the recurring features that may appear in cultivated fields, such as ridges. A new method for the calculation of drainage area in ridged fields was developed. Monte Carlo simulations showed a significant difference in estimated potential wetness between the new ¡¥ridged¡¦ and old methods. Simulation of soil moisture from three spatially distributed hydrological models, TOPMODEL, SMR and MIKE SHE, on the investigated fields ensued. The models all have a pronounced topographical driving force for the movement of water. The models were evaluated against observed soil moisture for two fields during two growing seasons. A correlation between simulated and observed soil moisture gave overall low correlation, 0.03 for SMR and MIKE SHE. It was concluded that the sole use of topography in explaining yield or estimating soil moisture is not enough. The spatial hydrological models tested need more tests on agricultural scale before they can be integrated into irrigation management systems.
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| 15. |
- Persson, Andreas, et al.
(författare)
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Why a leisure context is linked to normbreaking for some girls and not others : personality characteristics and parent–child relations as explanations
- 2004
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Ingår i: Journal of Adolescence. - : Wiley. - 0140-1971 .- 1095-9254. ; 27:5, s. 583-598
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Tidskriftsartikel (refereegranskat)abstract
- In a study of adolescents in the 1970s, girls were high in normbreaking if they attended youth recreation centers and were heavily involved with peers or boys (Stattin et al., 2003). The present study investigated whether these results could be replicated on a modern sample, and then examined parent–child relationships and personality characteristics as explanations why some girls and not others go to the youth centers and become heavily involved with peers and boys. Participants were 1279 14-year olds from a city in central Sweden. The results showed that personality characteristics and experiences at home partly explained youth center attendance, and personality characteristics partly explained involvement with boys, but neither explained why those who attended the centers and were involved with boys were highest on normbreaking. Thus, personality characteristics and experiences at home seem to be involved when girls choose the youth center context, but socialization by peers at the centers might better explain normbreaking among center goers.
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| 16. |
- Persson, Bertil, et al.
(författare)
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Betonguttorkning med byggcement
- 2000
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Ingår i: Bygg & teknik. - 0281-658X. ; , s. 30-32
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- I denna artikel redogörs för uttorkning hos betong med Byggcement jämfört med andra cementsorter: Slite Std-cement samt anläggningscement. Inverkan av silikastoft på uttorkningen hos Slite Std-cement redovisas. För ändamålet studerades 14 betonger upp till ett halvt år. Inverkan av självuttorkning, lufthärdning och vattenlagring fanns med i programmet. Resultaten visar att uttorkningen i huvudsak följer vattencementtalet, dvs eftersom Byggcement innehåller cirka åtta procent mindre rent cement än vad Slite Std-cement gör, får man räkna med något sämre självuttorkning vid användning av Byggcement jämfört med självuttorkningen i betong med Slite Std-cement.
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| 17. |
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| 18. |
- Persson, Kristina, et al.
(författare)
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Analytical considerations for free protein S assays in protein S deficiency
- 2001
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Ingår i: Thrombosis and Haemostasis. - 0340-6245. ; 86:5, s. 1144-1147
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Tidskriftsartikel (refereegranskat)abstract
- Protein S is an anticoagulant protein that circulates in plasma in complex with C4b-binding protein; (C4BP) or in free form. Deficiency of protein S increases the risk of venous thrombosis. Measurement of free protein S, as compared to total levels, has been shown to be superior for prediction of protein S deficiency. We studied the effects of different handling protocols for an immuno- and a ligand (C4BP)-based assay for free protein S. When the assay was performed at 37 degrees C, the levels of free protein S in plasma from protein S deficient patients were approximately twice those obtained at room temperature. The reason for this phenomenon was that plasmas from protein S deficient patients exhibited a time-, temperature-, and dilution-dependent increase in free protein S, which, was more pronounced than corresponding dilution of the normal plasma that was used to create the standard curve. These findings demonstrate the importance of assay procedure and sample handling in assays for free protein S.
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| 19. |
- Persson, Kristina, et al.
(författare)
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Använd hela "analyspaketet" vid utredning av trombospatienten! Och glöm inte släktingarna ...
- 2000
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Ingår i: Läkartidningen. - 0023-7205. ; 97:47, s. 5452-5456
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Tidskriftsartikel (refereegranskat)abstract
- During the last few years several genetic markers have been discovered that contribute to an increased risk of venous thrombosis. Patients who have several genetic markers are at a considerably higher risk of being affected than patients with only one marker. Recommendations are made as to which patients should be investigated, with appropriate laboratory analyses, when an increased risk of venous thrombosis is suspected. Most of the analyses can be done even if the patient is undergoing warfarin treatment.
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| 20. |
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