| 1. |
- Gustafsson, D, et al.
(författare)
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Effects of calcium antagonists on myogenic and neurogenic control of resistance and capacitance vessels in cat skeletal muscle
- 1988
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Ingår i: Journal of Cardiovascular Pharmacology. - 0160-2446. ; 12:4, s. 22-413
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Tidskriftsartikel (refereegranskat)abstract
- The effects of five different calcium antagonists (diltiazem, felodipine, nifedipine, nimodipine, and verapamil) on cat skeletal muscle resistance and capacitance vessels were studied in a whole organ preparation. These calcium antagonists seemed to have the similar qualitative effects on these vascular functions. Calcium antagonists were found to be potent inhibitors of myogenic vascular reactivity (here defined as the maximal increase in flow resistance evoked by a sudden rise of transmural pressure). Basal vascular tone and vascular tone induced by low frequency stimulation of sympathetic nerves were both less sensitive to these drugs than vascular tone induced by myogenic vascular reactivity. Sympathetically mediated vascular tone at high stimulation frequencies seemed to be least sensitive. Further, resistance vessels were much more sensitive to these drugs than capacitance vessels. Finally, basal tone in the large bore arterioles were more sensitive than in the small bore arterioles, a surprising finding which was interpreted with the aid of computer simulations using a mathematical model of local vascular control in cat skeletal muscle. The model suggested that this difference could be due to a delicate interaction between myogenic vascular reactivity and metabolic vascular control. It is suggested that the inhibition of myogenic vascular reactivity is a factor contributing to the edema formation of calcium antagonists.
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| 2. |
- Lindberg, Henrik, et al.
(författare)
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Chlorine loss and mass loss from Polyvinylchloride and polyvinylidenchloride under the electron beam
- 1985
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 20:6, s. 2225-2232
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Tidskriftsartikel (refereegranskat)abstract
- The loss of chlorine during the irradiation of PVC and PVDC in the electron microscope has been measured by the decay of the X-ray chlorine Kα signal. A number of factors affecting the measured beam damage curves have been considered and the experimental errors reduced to ±10%. The results show that the chlorine decay curves can be best described by the sum of two exponentials, corresponding to the two different chlorine decay processes, these being: the dehydrochlorination of the polymer molecules and the dehydrochlorination of the polyene structure formed by the beam damage. The higher initial chlorine content of PVDC compared to PVC will result in a larger amount of chlorine atoms reacting with the polyene structure, which is more stable in the electron beam than the undamaged polymer. The chlorine loss, measured by X-ray analysis, has been compared to the mass loss, measured by energy loss analysis, and also with the volume changes of isolated spherical PVC particles. It has been concluded that the mass loss is almost entirely due to chlorine loss and that the residual structure has a density similar to the undamaged PVC.
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| 3. |
- Lindberg, Henrik, et al.
(författare)
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Electron beam damage of some chlorine containing polymers and PVC blends
- 1989
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 24:8, s. 2825-2832
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Tidskriftsartikel (refereegranskat)abstract
- The electron beam damage of PVC, PVDC, chlorinated PE, chlorosulphonated PE (Hypalon) and chloroendic acid polyester has been studied by chlorine loss and mass loss measurements. The mass loss decay curves have been recalculated for true mass loss and correlated with the X-ray measurements of chlorine loss. It is shown that the major mechanism of degradation in these polymers is dehydrochlorination. The rate of dehydrochlorination is dependent on the chemical structure of the polymer, and in particular on the availability of hydrogen for HCl formation. However, in case of chloroendic acid polyester, more complicated volatile chlorinated compounds are also formed. The dehydrochlorination rate and mass loss of miscible PVC blends, namely PVC with organotin stabilizer, PMMA, PCL and SAN have been studied. The rate of chlorine loss from PVC was found to be unchanged for all blends except for PMMA and PCL, where it slightly increased due to the chemical reaction between the molecular fragments of both polymers. The differences between the thermal degradation and electron beam damage are also discussed.
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