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- Bystedt, Jan E. V., 1946-
(författare)
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Radiokontinuum-observationer av Andromedagalaxen med Westerborkteleskopet
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis, which consists of two articles in English and a summary in Swedish, deals with observations of the radio continuum emission from the Andromeda galaxy (M3D as observed with the Westerbork synthesis radio telescope in the Netherlands at 610 MHz. The work is part of a large effort to map M31 in the continuum at 1415 and 610 MHz, as well as in the 21 cm line of neutral hydrogen. Article I is a presentation of observations, data reduction, and the 36W catalogue of 392 radio sources in and around M31. A description of the addition of Bonn 100-m telescope data to the Westerbork measurements and of the removal of the discrete sources from the map is given. In article II a preliminary discussion is given of the extended emission from M31 itself. The radio continuum is mainly coming from the optically brightest arms, which seem to have a two-armed, trailing, structure, and are three times thicker than the neutral hydrogen layer. A lot of fine structure on scales < 100 pc is present in the map. Several HII regions are detected as 36W radio sources, and the smallest appear to be heavily obscured by dust. In the spiral arms there is evidence of instabilities forming moderate size cloud complexes.
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| 3. |
- van Dijken, Jan W. V., 1947-
(författare)
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Conventional, microfilled and hybrid composite resins : laboratory and clinical evaluations
- 1987
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three types of composite resins, classified as conventional, microfilled and hybrid resins were compared with respect to surface characteristics, effect on the gingival margin, marginal adaptation and clinical durability in anterior cavities.The surface characteristics were studied in in vitro systems by means of scanning electron microscopy. Fillings prepared in vivo were evaluated regarding surface characteristics, marginal conditions, color stability and the effect on the development of gingivitis and caries.Microfilled resins were superior to the conventional and hybrid composites with regard to the possibility of obtaining and retaining a smooth surface. The number of porosities varied greatly between the composites investigated and could not be related to the type or curing method used in their manufacture. Marginal defects in the form of chip fractures and fractures in the resin parallel to the resin/enamel border were seen more frequently in the microfilled composite fillings than in the conventional and hybrid resins. The severity of the defects increased with time.There was a great variation in clinical behaviour within each resin group. The difference in surface characteristics between the three composites did not result in clinically measurable differences in amount of plaque on and degree of gingivitis around the composite fillings neither during a period of normal home care nor during an experimental gingivitis period. Recurrent caries was the major single reason for replacement. Patients with a greater number of caries risk factors clearly showed a higher caries increment, especially around composite fillings. The shortcomings of the three composite resin types indicate that no material as yet meets the demands of an all purpose material.
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