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- Alm, Fredrik, 1971-
(författare)
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Uttryck på schemat och intryck i klassrummet : En studie av lektioner i skolor utan timplan
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med föreliggande avhandling är att studera användning och förekomst av lektionsbeteckningar på scheman i skolor utan en nationellt fastställd timplan, samt belysa hur elever upplever de lokala val som görs vad gäller vissa av dessa lektionsbeteckningar. Den teoretiska referensramen har sin grund i didaktikens selektionsfråga och kommunikationsfråga, och Bernsteins båda begrepp klassifikation och inramning. Avhandlingen består av två delstudier. I delstudie I analyseras, såväl kvalitativt som kvantitativt, 326 scheman från 33 skolor som på försök arbetar utan timplan. 163 scheman från skolor med timplan har analyserats i jämförande syfte. I delstudie II genomförs tio gruppintervjuer med totalt 41 elever kring tre typer av icke ämnesrelaterade lektionsbeteckningar (lagtid, verkstad och mentorstid), som är vanligt förekommande på elevers scheman. I avhandlingen visas att en mängd schemabeteckningar (170 stycken) används för att beskriva vad elever och lärare ämnar ägna sig åt. Utöver traditionella ämnen, schemaläggs arbetsmetoder, gruppbaserad tid, skriv- och lästid, social samspelstid, rekreationstid samt lektioner där eleverna involveras i val, planering och utvärdering. Den här typen av alternativa schemabeteckningar används i signifikant större utsträckning i skolorna utan timplan och i de tidigare årskurserna. När skolorna utan timplan använder alternativa beteckningar leder det huvudsakligen till schemapositioner med svagare inramning och svagare klassifikation, samt en förskjutning från innehåll mot metod/form. Eleverna upplever att lektionerna med svagare inramning och klassifikation har ett värdefullt och verklighetsanknutet innehåll, men att de inte är lika viktiga som ämnena. De upplevs ibland vara slöseri med lektionstid. Resultaten diskuteras i ljuset av annan forskning om skolor utan timplan och avhandlingens didaktiska perspektiv.
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- Berg, Anna, 1975-
(författare)
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Effects of nitric oxide on gastric acid secretion in human gastric mucosa : functional and morphological studies
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrochloric acid (HCI) is secreted in high amounts by parietal cells in the human gastric mucosa and the resulting low pH constitutes an important factor for creating a suitable environment for the digestion. The normal gastric mucosa is equipped with an arsenal of protective mechanisms against the extreme chemical environment which the gastric acid creates. There are situations when the barrier function of the gastric mucosa is disrupted and gastric acid becomes potentially deleterious. Understanding the regulatory mechanisms by which the secretion of gastric acid is controlled under physiological conditions may improve future treatment in peptic ulcers, gastritis and other gastric inflammatory disorders.Nitric oxide (NO) has previously been found to regulate gastric acid secretion in animals. Immunohistochemical investigation of normal human gastric mucosa revealed that hitherto unknown endocrine cells in the oxyntic mucosa express nitric oxide synthase (NOS). These cells were found located in close contact with parietal cells, which suggests a paracrine effect of NO on parietal cell function.Functional studies of the effects of exogenous and endogenous NO on stimulated gastric acid secretion were performed on isolated human gastric glands. Indirect determination of gastric acid secretion by using the 14C-labeled aminopyrine (AP) technique was used. Stimulation was induced by administration of histamine or db-cAMP. Secretagogue-induced AP-accumulation in gastric glands treated with NO-donor was significantly decreased compared with untreated glands. This indicates that exogenously administered NO inhibits stimulated gastric acid secretion in humans. Inhibition of endogenous NO-production by the use of NOS-inhibitors caused an increase in AP-accumulation, which suggests that NO released from cells within the glandular epithelium exerts a physiological effect in acting as an inhibitor of stimulated gastric acid secretory activity in humans.Further functional and morphological investigations showed that exogenously administered cGMP induced a concentration-dependent inhibition of AP-accumulation in isolated human gastric glands similar to that induced by NO-donors. When soluble guanylate cyclase (sGC), a common target enzyme for NO, was blocked NO failed to induce inhibition. Biochemical analysis of the cGMP concentrations in isolated gastric glands after treatment with NO-donor revealed that inhibition of AP-accumulation due to NO is accompanied by an increase in glandular cGMP content. This increase was localized by immunohistochemistry to the parietal cells. These results indicates that NO inhibits secretagogue-induced gastric acid secretion in isolated human gastric glands via activation of sGC, which results in an increased concentration of cGMP in the parietal cells.In order to determine the cGMP-dependent mechanisms leading to diminished output of gastric acid, parietal cells were investigated with emphasis on the cytological transformations associated with stimulation of acid secretion. Isolated human gastric glands were treated with NO-donor prior to administration of histamine. The cytoskeletal rearrangement as well as the translocation and incorporation of H+/K+-ATPase into the apical membrane was studied using con focal and electron microscopy techniques. Results showed that histamine-induced F-actin rearrangement as well as the translocation of H+/K+-ATPase rich tubulovesicles to the canalicular membrane, and their fusion with the same, was unaffected by NO. The secretory canaliculi, which swell to great size as a result of histamine-treatment, were however small and unexpanded in response to treatment with NO-donor. The unexpanded canaliculi reflected the NO-induced inhibition of secretion of HCI observed in the functional studies.In conclusion, these results show that NO may be a physiological regulator of stimulated gastric acid secretion in humans and that this inhibition is a cGMP-dependent mechanisms which diminishes output of HCI from parietal cells without affecting stimuli-induced cytological transformations.
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- Berg, Björn, et al.
(författare)
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Reduction of decomposition rates of Scots pine needle litter due to heavy-metal pollution
- 1991
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Ingår i: Water, Air and Soil Pollution. - 1573-2932. ; 59:1-2, s. 165-177
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition of unpolluted Scots pine needle litter was studied in two heavy-metal-pollution gradients in Sweden; one near a brass mill and the other around a primary smelter. In the latter area locally collected polluted Scots pine needle litter was also incubated. Decomposition rates were strongly influenced by the metal pollution and a decrease in the rate of mass-loss occurred. In the brass-mill gradient this occurred until about 1 km from the pollution source which corresponded to about 500-mu-g Cu and 1000-mu-g Zn g-1 soil. Data are presented to indicate that lignin decomposition was more sensitive to pollution than decomposition of whole litter and affected further away from the pollution sources. At the smelter sites, the metal-polluted needle litter decomposed more slowly than the unpolluted needle litter, and this difference was enhanced close to the smelter. The results indicate that heavy metals accumulated in needles prior to shedding have a long-term impact on the subsequent decomposition of the litter. Both litter quality and soil factors thus contribute to the reduced litter decomposition rate in metal-polluted forests. A new non-linear model with decreasing decay rate was used in the statistical evaluation. The model can be used to characterize the effects of pollution on decomposition rate.
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