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- Ackelid, U, et al.
(författare)
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Kinetics of ethylene oxidation on plane Pt/SiO2 catalysts in the viscous pressure regime: Evidence of support activity
- 1996
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Ingår i: Catalysis Letters. - 1011-372X. ; 39:1-2, s. 129-139
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Tidskriftsartikel (refereegranskat)abstract
- C2H4 oxidation on plane Pt/SiO2 model catalysts with various Pt loadings was studied at T = 373-473 K and in the pressure ranges 10-6-102 Torr C2H4 and 0.3-1500 Torr O2 (1 Torr = 133.3 Pa). Mass spectrometry combined with spatially resolved gas sampling enabled kinetic data to be collected far into the viscous pressure regime. Reaction orders and activation energies were similar to those of a macroscopic Pt surface. However, under fuel-lean conditions the global reaction rate decreases faster than the decrease in metal area. On the other hand, the global rate was independent of Pt loading and metal surface area in fuel-rich gas mixtures. This is interpreted in terms of a spillover effect.
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- Twetman, S, et al.
(författare)
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Comparison of the efficacy of three different chlorhexidine preparations in decreasing the levels of mutans streptococci in saliva and interdental plaque
- 1998
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Ingår i: Caries research. - : S. Karger AG. - 0008-6568 .- 1421-976X. ; 32:2, s. 113-118
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Tidskriftsartikel (refereegranskat)abstract
- The aim of the present study was to evaluate and compare the effects of three different chlorhexidine (CHX)-containing preparations on mutans streptococci (MS) levels in interdental plaque and whole saliva. Ninety-three healthy schoolchildren (8–10 years old) with high scores of salivary MS were selected by a screening procedure and randomised into three equally sized groups. MS were enumerated at all mesial interdental sites of the first permanent molars with aid of a modified chairside technique. The patients were then treated three times within 2 weeks with either a 1% CHX/thymol-containing varnish (group A) or a 1% CHX gel (group B), or they were subjected to daily supervised toothbrushing with a 0.4% CHX dentifrice for 1 month (group C). Follow-up samples of saliva and plaque from the interdental sites were collected 1 and 3 months after termination of treatment. A statistically significant reduction of MS levels in saliva and interdental plaque was found in all groups after 1 month. The CHX-containing dentifrice (group C) was the most effective method in reducing MS levels in saliva, and a significantly stronger (p < 0.05) suppression was found after 1 and 3 months when compared with the gel and the varnish forms. The gel (group B) tended to be slightly more effective than the varnish (group A). In the interdental plaque, the reduction of MS was less marked than in the saliva, and the three groups exhibited MS reductions of similar magnitude (20%) and duration, persisting up to 3 months. However, a high proportion (approximately 50%) of all interdental sites were relatively unaffected by the treatments. In conclusion, our results suggest that the interdental MS colonisation was difficult to combat, irrespective of CHX preparation and method, while the salivary levels were more easily affected. Daily tooth-brushing with a CHX-containing dentifrice was more effective in reducing MS in saliva compared with the gel or varnish applications.
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