| 61. |
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| 62. |
- Bidleman, TF, et al.
(författare)
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Chiral pesticides as tracers of air-surface exchange
- 1998
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Ingår i: Environmental Pollution. - 0269-7491 .- 1873-6424. ; 102:1, s. 43-49
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Tidskriftsartikel (refereegranskat)abstract
- The enantiomers of chiral pesticides are selectively broken down in soil and water to yield residues and metabolites, which are non-racemic. The distinctive enantiomer signatures of residues are preserved upon volatilization, providing site-specific tracers for air-soil and air-water exchange. Applications of enantiomeric tracers include distinguishing the atmospheric transport of freshly applied pesticides from those which are 'recycled' from lakes, oceans and soil, and investigating biotic vs abiotic degradation pathways. Examples are given of using pesticide enantiomers to follow volatilization from the Great Lakes and arctic waters and as indicators of pesticide emissions from agricultural soils.
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| 63. |
- Bidleman, TF, et al.
(författare)
-
Soil as a source of atmospheric heptachlor epoxide
- 1998
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 32:10, s. 1546-1548
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Tidskriftsartikel (refereegranskat)abstract
- The chiral pesticide heptachlor can undergo photolysis to yield the racemic products heptachlor-exo-epoxide (HEPX) and photoheptachlor. Heptachlor is also metabolized to nonracemic HEPX in biological systems and soils. HEPX in ambient air samples from the southern United States and Lakes Ontario and Superior was nonracemic and enriched in the (+) enantiomer. Average enantiomer ratios (ER = areas of (+)/(-) HEPX) in these locations ranged from 1.51 to 2.02, and were similar to ER values of HEPX reported for agricultural soils. Airborne heptachlor was racemic, with ERs of 0.98-1.02. These results suggest that the main source of HEPX in ambient air is not photolysis of heptachlor, hut rather metabolism of heptachlor in soils followed by volatilization of HEPX. The study exemplifies the use of chiral analysis for investigating the environmental fate of pesticides.
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| 64. |
- Billker, Oliver, et al.
(författare)
-
Identification of xanthurenic acid as the putative inducer of malaria development in the mosquito
- 1998
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Ingår i: Nature. - : Macmillan Publishers Ltd.. - 0028-0836 .- 1476-4687. ; 392:6673, s. 289-292
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Tidskriftsartikel (refereegranskat)abstract
- Malaria is transmitted from vertebrate host to mosquito vector by mature sexual blood-living stages called gametocytes. Within seconds of ingestion into the mosquito bloodmeal, gametocytes undergo gametogenesis. Induction requires the simultaneous exposure to at least two stimuli in vitro: a drop in bloodmeal temperature to 5 degrees C below that of the vertebrate host, and a rise in pH from 7.4 to 8.0-8.2. In vivo the mosquito bloodmeal has a pH of between 7.5 and 7.6. It is thought that in vivo the second inducer is an unknown mosquito-derived gametocyte-activating factor. Here we show that this factor is xanthurenic acid. We also show that low concentrations of xanthurenic acid can act together with pH to induce gametogenesis in vitro. Structurally related compounds are at least ninefold less effective at inducing gametogenesis in vitro. In Drosophila mutants with lesions in the kynurenine pathway of tryptophan metabolism (of which xanthurenic acid is a side product), no alternative active compound was detected in crude insect homogenates. These data could form the basis of the rational development of new methods of interrupting the transmission of malaria using drugs or new refractory mosquito genotypes to block parasite gametogenesis.
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| 65. |
- Binzer, M, et al.
(författare)
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Illness behavior in the acute phase of motor disability in neurological disease and in conversion disorder : a comparative study.
- 1998
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Ingår i: Journal of Psychosomatic Research. - 0022-3999 .- 1879-1360. ; 44:6, s. 657-66
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Tidskriftsartikel (refereegranskat)abstract
- Sixty patients with a sudden onset of motor disability were assessed for illness behavior and depression. In 30 of the patients, etiology was attributed to a definite structural lesion. The remaining 30 patients were diagnosed as having conversion disorder. The Illness Behaviour Questionnaire (IBQ) and the Hamilton Rating Depression Scale (HRDS) were used as instruments for assessment. The mean HRDS score was significantly higher in the conversion group, indicating a higher degree of affective disease in these patients. According to the results of the IBQ, the patients with conversion disorder showed a higher degree of irritability, disease conviction, and phobic preoccupation, and also, to a greater extent, rejected psychological explanations for their symptoms. Denial was high in both patient groups, coexisting with affective symptoms in the conversion patients but not in the neurological patients. Although valuable information could be extracted from the IBQ, it was not found to be a reliable instrument for distinguishing between psychogenic and organic causes of motor disability.
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| 66. |
- Binzer, M, et al.
(författare)
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Motor conversion disorder. A prospective 2- to 5-year follow-up study.
- 1998
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Ingår i: Psychosomatics. - 0033-3182 .- 1545-7206. ; 39:6, s. 519-27
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Tidskriftsartikel (refereegranskat)abstract
- In this prospective study, 30 patients with motor conversion disorder were assessed for key psychiatric and demographic variables. At reassessment 2 to 5 years later, 19 patients had completely recovered and 8 patients had improved, whereas only 3 were unchanged or worse. Contrary to other follow-up studies, none of the patients received a rediagnosis of neurological disease. The presence of a personality disorder and overall personality pathology, particularly within cluster C, the presence of a concomitant somatic disease, low DSM-IV Axis V score, and high score on the Becks Hopelessness Scale proved to be associated with poor outcome.
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| 67. |
- Birznieks, Ingvars, et al.
(författare)
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Mechanisms for force adjustments to unpredictable frictional changes at individual digits during two-fingered manipulation.
- 1998
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Ingår i: Journal of Neurophysiology. - 0022-3077 .- 1522-1598. ; 80:4, s. 1989-2002
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies on adaptation of fingertip forces to local friction at individual digit-object interfaces largely focused on static phases of manipulative tasks in which humans could rely on anticipatory control based on the friction in previous trials. Here we instead analyze mechanisms underlying this adaptation after unpredictable changes in local friction between consecutive trials. With the tips of the right index and middle fingers or the right and left index fingers, subjects restrained a manipulandum whose horizontal contact surfaces were located side by side. At unpredictable moments a tangential force was applied to the contact surfaces in the distal direction at 16 N/s to a plateau at 4 N. The subjects were free to use any combination of normal and tangential forces at the two fingers, but the sum of the tangential forces had to counterbalance the imposed load. The contact surface of the right index finger was fine-grained sandpaper, whereas that of the cooperating finger was changed between sandpaper and the more slippery rayon. The load increase automatically triggered normal force responses at both fingers. When a finger contacted rayon, subjects allowed slips to occur at this finger during the load force increase instead of elevating the normal force. These slips accounted for a partitioning of the load force between the digits that resulted in an adequate adjustment of the normal:tangential force ratios to the local friction at each digit. This mechanism required a fine control of the normal forces. Although the normal force at the more slippery surface had to be comparatively low to allow slippage, the normal forces applied by the nonslipping digit at the same time had to be high enough to prevent loss of the manipulandum. The frictional changes influenced the normal forces applied before the load ramp as well as the size of the triggered normal force responses similarly at both fingers, that is, with rayon at one contact surface the normal forces increased at both fingers. Thus to independently adapt fingertip forces to the local friction the normal forces were controlled at an interdigital level by using sensory information from both engaged digits. Furthermore, subjects used both short- and long-term anticipatory mechanisms in a manner consistent with the notion that the central nervous system (CNS) entertains internal models of relevant object and task properties during manipulation.
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| 68. |
- Blackburn, Nicholas, et al.
(författare)
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Rapid determination of bacterial abundance, biovolume, morphology, and growth by neural network-based image analysis
- 1998
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Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 64:9, s. 3246-3255
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Tidskriftsartikel (refereegranskat)abstract
- Annual bacterial plankton dynamics at several depths and locations in the Baltic Sea were studied by image analysis. Individual bacteria were classified by using an artificial neural network which also effectively identified nonbacterial objects, Cell counts and frequencies of dividing cells were determined, and the data obtained agreed well with visual observations and previously published values. Cell volumes were measured accurately by comparison with bead standards. The survey included 690 images from a total of 138 samples. Each image contained approximately 200 bacteria. The images were analyzed automatically at a rate of 100 images per h, Bacterial abundance exhibited coherent patterns with time and depth, and there were distinct subsurface peaks in the summer months. Four distinct morphological classes were resolved by the image analyzer, and the dynamics of each could be visualized. The bacterial growth rates estimated from frequencies of dividing cells were different from the bacterial growth rates estimated by the thymidine incorporation method. With minor modifications, the image analysis technique described here can be used to analyze other planktonic classes.
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| 69. |
- Blomquist, M, et al.
(författare)
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Measured lung dose correction factors for 50 MV photons
- 1998
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 43:11, s. 3225-3234
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Tidskriftsartikel (refereegranskat)abstract
- Some clinically relevant measurements of lung tissue/water equivalent interfaces have been performed for a 50 MV therapeutic x-ray beam. The purpose was to investigate the severity of dose perturbation effects in lung tissue and adjacent tissues using an energy well above the common clinical practice in thoracic irradiations. The phantoms were constructed of solid water, PMMA and white polystyrene as soft tissue (water) equivalents, and cork was used as the lung tissue equivalent. Measurements were performed using radiographic film and a cylindrical ionization chamber. The results show that the degradation of the 20/80% beam penumbra in the lung region is severe, up to 2.5 times the penumbra in water for a 10 cm thick lung with a density of 0.30 x 10(3) kg m(-3). The lack of electronic equilibrium in the low-density region can cause underdosage at the lung/tumour interface of up to 30% of maximum target dose, and the build-up depth to 95% of target dose in unit density tissue behind the lung may be as large as 22 mm. It is also shown that these figures strongly depend on patient anatomy and beam size and why a careful calculation of the individual dose distribution is needed for optimal choice of photon beam energy in thoracic treatments.
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| 70. |
- Blomquist, M, et al.
(författare)
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Scanned intensity modulations for 50 MV photons
- 1998
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Ingår i: Physics in Medicine and Biology. - 0031-9155 .- 1361-6560. ; 43:5, s. 1185-1197
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Tidskriftsartikel (refereegranskat)abstract
- Optimization of the dose distributions by individual beam compensation is a useful tool in conformal radiation therapy. Intensity modulation by electromagnetic scanning of a narrow elementary beam allows fast dose delivery and causes little change in beam quality compared with other methods, especially for high energies such as 50 MV. Intensity modulated beams from the MM50 accelerator were measured and compared with calculations based on Monte Carlo simulations. Good agreement between measurements and calculations were found, typically within 1% for central dose profiles. The steepest wedge angle that was produced with the scanning beam technique was of 45 degrees or 3.5% cm(-1) for a 20 cm x 20 cm field, slightly varying with depth. The elementary 50 MV photon 'pencil beam' for a full range, high-z bremsstrahlung target, is a wide dose distribution at 10 cm depth in water which limits the modulation gradient and hence the complexity of the modulation by the scanning of a photon pencil beam only. Scanned wedge beam distributions were modelled in the treatment planning system and a pelvic treatment with three fields was used to illustrate a clinical application. The resulting dose volume data were compared for different radiation qualities but with similar beam portals. 'Energy modulation' by field matching with lower photon energies was performed to sharpen the penumbra towards organs at risk.
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