Stein Nilsen

Wavelets applied to simplification of digital terrain models

Wavelet thresholding is used to generate simplified terrain models. This non-linear filtering technique is adaptive in the sense that the large wavelet coefficients in areas of high relief are kept, whereas all coefficients smaller than a threshold value, representing smooth areas, are thrown away. The degree of detail in the simplified model is controlled by the number of wavelet coefficients retained. Two different areas are analysed using this method. The experiments show the smoothing effect of the thresholding, and how the main terrain features survive as the threshold value increases. At large threshold values the method introduces blocking artifacts in the model.

Considerations made by the general practitioner when dealing with sick-listing of patients suffering from subjective and composite health complaints

Abstract Objectives. To explore GPs’ considerations in decision-making regarding sick-listing of patients suffering from SHC. Design. Qualitative analysis of data from nine focus-group interviews. Setting. Three cities in different regions of Norway. Participants. A total of 48 GPs (31 men, 17 women; aged 32–65) participated. The GPs were recruited when invited to a course dealing with diagnostic practice and assessment of sickness certificates related to patients with composite SHCs. Results. Decisions on sick-listing patients with SHCs were regarded as a very challenging task. Trust in the patients own story and self-judgement was deemed crucial, but many GPs missed hard evidence of illness and loss of function. Several factors that might influence decision-making were identified: the patients’ ability to present their story to evoke sympathy, the GPs prior knowledge of the patient, and the GPs’ own experience as a patient and their tendency to avoid conflicts. The approach to the task of sick-listing differed from patient-led cooperation to resistant confrontation. Conclusion and implications. Issuing sickness certification in patients with composite health complaints is considered challenging and burdensome. It is seen as mainly patient-driven, and the decisions vary according to GPs’ attitudes, beliefs, and personalities. Guiding the GPs to a more focused awareness of the decision process should be considered.

Barriers against returning to work – as perceived by disability pensioners with back pain: A focus group based qualitative study

Purpose. The aim of this study was to explore the issue of perceived barriers for returning to work, based on the experiences and beliefs in a group of disability pensioners with back pain. Method. Focus groups were used to interview 12 women and five men, aged 38 – 56, who participated in a larger project aiming to help disability pensioners back to work. Results. The barriers appearing were related to earlier negative experiences, poor self-judgement of work ability and low self-esteem, lack of support from social security authorities and unsuitable economic arrangements. The pensioners also suggested alternative solutions for making a possible return to work. Conclusions. Our study provides insight into the perceived barriers of returning to work and might be useful in future efforts aiming to help disability pensioners back to work.

Photoinhibition of photosynthesis: effect of light quality and quantity on recovery from photoinhibition in Lemna gibba

Summary The effect of darkness, light intensity and light excitation on one or both of the photosystems on the recovery from photoinhibition in Lemna gibba , was studied. Photoinhibition was induced by exposing plants to the photon flux of 1000 μmol m −2 s −1 in an N 2 atmosphere for 90 min. Photosynthetic CO 2 uptake was measured in a closed gas exchange system. Light stimulated restoration of the photosynthetic capacity, although some recovery occurred also in darkness. Recovery was shown to be independent of the photon flux of the light below the saturating level. Photon fluxes higher than this level, however, decreased recovery of the photosynthetic capacity. These data indicate the existence of damaging and repairing processes which occur simultaneously, and it appears that the balance between them depends on the photon flux of the light under recovery. The recovery of high light plants was significantly greater than of low light plants, irrespective of the photon flux used during the recovery period. This suggests that high light during cultivation somehow enables the photoinhibited plants to recover faster. Monochromatic light exciting mainly PS I produced a significantly higher recovery than when PS II was mainly excited, suggesting the importance of PS I in the recovery process. The results are discussed from the viewpoint of the possible biochemical mechanisms involved.

Effect of CO2 enrichment on photosynthesis, growth and yield of tomato

Abstract Net photosynthesis of tomato plants was measured as CO2 uptake in various light intensities, CO2 concentrations, O2 concentrations and temperatures during short-term experiments. Net photosynthesis increased significantly with increasing CO2 concentration at all light intensities, even at the lowest one. The optimal temperature for photosynthesis increased with CO2 enrichment. The changes in photosynthesis when the CO 2 O 2 ratio was varied suggest that the effect of CO2 enrichment is a result of a reduction in photorespiration. To determine whether the increase in photosynthesis caused by CO2 enrichment would produce a greater yield, tomato plants were cultivated from seed to harvest in a tightly-closed greenhouse that was enriched with CO2 continuously during the entire growing-period. The control greenhouse was ventilated by openings in the roof and door. The temperature of the 2 greenhouses was kept the same. Plants enriched with CO2 showed a significant increase in fresh and dry weight and yield of tomatoes. The results are discussed in relation to earlier work in which CO2 enrichment was discontinued when there was a need for ventilation.

Reduction of net photosynthesis in oats after treatment with low concentrations of ozone

Oats (Avena sativa L. cv Titus) were exposed to low concentrations of O3 in an assimilation chamber system. Net photosynthesis (net CO2 uptake), measured before and after O3 fumigation, showed significantly different responses for leaves of different age. The oldest active leaf was the most sensitive to O3. Net photosynthesis was depressed after 2 h with 0.075 ppm (150 microg m(-3)) O3. For leaves exposed to 0.150 ppm (300 microg m(-3)) O3 for 2 h, net photosynthesis was reduced significantly for 4 h, after which recovery occurred, nearly reaching the preexposure level 19 h after the exposure. Dark respiration was initially more than doubled after exposure to 0.130 ppm (260 microg m(-3)) O3. There was no visible injury after any of the experiments. The results indicate that O3 may cause crop losses through effects on photosynthesis even in Scandinavia, where a typical O3 episode lasts 1 to 2 h, and the concentration seldom exceeds 0.150 ppm.

Photoinhibition of photosynthesis in vivo: Involvement of multiple sites in a photodamage process under CO2- and O2-free conditions

Abstract Intact Lemna gibba plants were illuminated by photoinhibitory light in air, in air minus O 2 , in air minus CO 2 , and in pure N 2 . In pure N 2 , the degree of photoinhibition increased 3–5-times compared with that in air. This high degree of photoinhibition is described as photodamage. Photodamage was found to constitute a syndrome, that is, it is due to inactivation of multiple sites. These sites include RC II component(s) from P680 to Q A ; the Q B -site; and a component of PS I. In photodamage, the donor side of PS II and PS II excitation energy transfer remain unimpaired, but the size of the PS I antenna seems to decrease. Photodamage is distinguishable from photoinactivation. Photoinactivation occurred in air and could be attributed to inhibition of electron transport from Q − A to Q B . During photoinactivation the D1 protein of RC II became degraded faster than the detectable inhibition of Q B reduction. The photoinhibition-induced rise in F 0 occurred only during the process of photodamage but not during that of photoinactivation, and was a secondary event which arose as a consequence of photodamage. Atmospheric O 2 alleviated photodamage but increased photoinactivation. The light-induced D1 degradation and inhibition of Q A to Q B electron transfer were enhanced in vivo not only by O 2 but also by depletion of CO 2 .

Recovery from photoinhibition: effect of light and inhibition of protein synthesis of 32-kD chloroplast protein

Recovery from photoinhibition of photosynthesis in intact Lemna gibba was studied in presence of the protein synthesis inhibitors chloramphenicol and cycloheximide. Exposure to an irradiance of 1000 μmol m-2s-1 in N2 for 90 min induced 80% photoinhibition. The plants recovered photosynthesis when transfered to normal irradiances (210 μmol m-2s-1) and air. Chloramphenicol added to the medium was taken up by the plant and reduced photosynthesis slightly. Recovery from photoinhibition was more inhibited than photosynthesis. Cycloheximide was also taken up by the plants and reduced synthesis of light harvesting chlorophyll protein: however, neither photosynthesis nor recovery were much affected. Synthesis of 32-kD chloroplast protein during recovery was inhibited by chloramphenicol, but not by cycloheximide. Synthesis of 32-kD protein was enhanced by 20–210 μmol m-2s-1 light. The results support the hypothesis that synthesis of 32-kD protein is important for recovery of photosynthesis after photoinhibition.

Wavelet representation of large digital terrain models

Average interpolating wavelets are used to construct multilevel representations of large data sets. The data are partitioned into disjoint blocks, and each block is transformed separately. A new implementation of the wavelet algorithm guarantees that this partitioning does not introduce artificial boundary effects. Coefficients are organized in a data structure that is well suited for real-time visualization with zoom functionality.

Yield of tomato and maize in response to foliar and root applications of triacontanol

Triacontanol applied to tomato plants as a foliar spray caused a significant increase in total yield and yield per plant. When triacontantol was added to the growth medium, only a temporary increase in yield and number of fruits was observed. The yield of maize was unaffected by triacontanol, either applied to the leaves or to the growth substrate. These results support an earlier observation that a reduction in photorespiration is involved in the regulatory function of triacontanol, since only the yield of tomato, a C3 plant, was increased. The application method was an important factor in its effectiveness.