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- Choularton, T. W., et al.
(författare)
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The Great Dun Fell Cloud Experiment 1993 : An overview
- 1997
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Ingår i: Atmospheric Environment. - 1352-2310. ; 31:16, s. 2393-2405
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Tidskriftsartikel (refereegranskat)abstract
- The 1993 Ground-based Cloud Experiment on Great Dun Fell used a wide range of measurements of trace gases, aerosol particles and cloud droplets at five sites to study their sources and sinks especially those in cloud. These measurements have been interpreted using a variety of models. The conclusions add to our knowledge of air pollution, acidification of the atmosphere and the ground, eutrophication and climate change. The experiment is designed to use the hill cap cloud as a flow-through reactor, and was conducted in varying levels of pollution typical of much of the rural temperate continental northern hemisphere in spring-time.
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| 3. |
- Blomstrand, Fredrik, 1969, et al.
(författare)
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Extent of intercellular calcium wave propagation is related to gap junction permeability and level of connexin-43 expression in astrocytes in primary cultures from four brain regions.
- 1999
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Ingår i: Neuroscience. - 0306-4522. ; 92:1, s. 255-65
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Tidskriftsartikel (refereegranskat)abstract
- Astrocytes are coupled via gap junctions, predominantly formed by connexin-43 proteins, into cellular networks. This coupling is important for the propagation of intercellular calcium waves and for the spatial buffering of K+. Using the scrape-loading/dye transfer technique, we studied gap junction permeability in rat astrocytes cultured from four different brain regions. The cultures were shown to display regional heterogeneity with the following ranking of the gap junction coupling strengths: hippocampus = hypothalamus > cerebral cortex = brain stem. Similar relative patterns were found in connexin-43 messenger RNA and protein levels using solution hybridization/RNase protection assay and western blots, respectively. The percentages of the propagation area of mechanically induced intercellular calcium waves for cortical, brain stem and hypothalamic astrocytes compared with hippocampal astrocytes were approximately 77, 42, and 52, respectively. Thus, the extent of calcium wave propagation was due to more than just gap junctional permeability as highly coupled hypothalamic astrocytes displayed relatively small calcium wave propagation areas. Incubation with 5-hydroxytryptamine decreased and incubation with glutamate increased the calcium wave propagation area in hippocampal (67% and 170% of the control, respectively) and in cortical astrocytes (82% and 163% of the control, respectively). Contrary to hippocampal and cortical astrocytes, the calcium wave propagation in brain stem astrocytes was increased by 5-hydroxytryptamine incubation (158% of control), while in hypothalamic astrocytes, no significant effects were seen. Similar effects from 5-hydroxytryptamine or glutamate treatments were observed on dye transfer, indicating an effect on the junctional coupling strength. These results demonstrate a strong relationship between connexin-43 messenger RNA levels, protein expression, and gap junction permeability among astroglial cells. Furthermore, our results suggest heterogeneity among astroglial cells from different brain regions in intercellular calcium signaling and in its differential modulation by neurotransmitters, probably reflecting functional requirements in various brain regions.
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| 5. |
- Jacobsen, Sissel N.
(författare)
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Growth, Characterization, and Thermal Stability of CeO2 Thin Films
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rare earth oxides are potentially useful materials in various optical electronic, and catalytic devices. The characteristics of such devices are strongly dependent on the interface structure of heterojunctions, hence engineering of the performance can be achieved through tailoring of the micro- and/ or surface structure. In this thesis thin films of cerium dioxide(Ce02) are investigated, with the aim of realising Ce02 films with a welldefined microstructure and surface crystallography.Ce02 thin films have been sputter deposited in a reactive oxygen/ argon atmosphere at a substrate temperature of 800 °C on α - Al203 (102), LaAl03 (001), and MgO (111) substrates. The microstructure, orientation, surface morphology and chemical state of the Ce02 films have been investigated by a combination of transmission electron microscopy (TEM), x-ray diffraction (XRD), atomic force microscopy(AFM), x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS).The Ce02 films are shown to grow with an epitaxial relation to the α-Al203 substrate, with Ce02 (001) ║ Al203 (102). TEM reveals a microstructure with highly oriented columns parallel to the growth direction. Upon close examination a faceted top surface terminated by {111} planes can be observed. In order to examine possible changes in the surface morphology or the crystalline quality of the CeO2 layers, selected samples were post-deposition annealed at various temperature and gas ambient. Annealing at 850 °C in Ar/ 02 render a truncation of the extremely sharp microfacets on the CeO2 surface as verified by high resolution TEM (HREM). AFM analysis establish the formation of a flat surface morphology through annealing at higher temperatures in Ar, and XPS show an accompanying reduction in the oxidation state of Ce4+. Identical annealing procedures in 02 prevent, to a high degree, such reduction reactions, however, at high temperatures, the film layer is no longer continuous, but rather a network of material on the substrate surface.When a YBa2Cu3O7-x (YBCO) is sputtered on CeO2 - buffered α-Al2O3 HREM reveals a remarkably smooth interface between the YBCO and CeO2 layers. Also, the microwave surface resistance is comparable to that of YBCO films grown directly on single-crystalline substrates, being approximately 185 mW at 6,1 Ghz.The total sputtering pressure,P significantly influence the orientation and surface morphology of CeO2 thin films grown on α-Al2O3(102) substrates, using both off-axis and on-axis substrate/magnetron configurations. XRD analysis show that growth at 12.9 Pa favor the (001)CeO2 orientation giving a rough surface morphology, while decreasing the pressure to 0.4 Pa results in a (111) CeO2 preferred orientation with a relatively smooth surface morphology. Additionally, RBS examination reveal a stoichiometric film composition with abrupt interfaces. Identical studies on CeO2 films grown on LaA1O3 substrates show no observable change in film orientation, however the surface roughness varies with the total pressure in a similar way to that of films on Al2O3.The CeO2 films exhibit a strong epitaxial preference on MgO (111), with Ce02 (111)│MgO(111) in the case of thicker films. The top surfaces of these films are characterized by fairly flat areas, exposing the (111)-surface of the CeO2 crystal, interrupted by a few, taller (001)-oriented grains. However, thin ( 20 nm) CeO2 films consist of islands that exhibit a preferred (001) orientation.
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| 9. |
- Jensen, N, et al.
(författare)
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Recovery of endothelial cells and prostanoid production in endothelial cell-seeded grafts
- 1996
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Ingår i: European Journal of Vascular and Endovascular Surgery. - 1532-2165. ; 12:1, s. 54-59
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To investigate the function and morphology of endothelial cell (EC) seeded grafts. DESIGN: Experimental, open study. CHIEF OUTCOME MEASURES: Endoluminal release of prostacyclin (6-Keto-PGF1 alpha) and thromboxane B2 (TxB2), patency, EC coverage and cell identity. MATERIALS: In 12 sheep, segments of both carotid arteries were excised. On one side a seeded and on the other an unseeded dacron graft were inserted. After 3 months the grafts were excised. In grafts and arteries, the endoluminal release of 6-keto-PGF1 alpha and TxB2 was determined in a perfusion system. Scanning electron microscopy (SEM) and light microscopy were used to determine the EC coverage and cell identity. RESULTS: Eight animals survived. Three seeded and two unseeded grafts were occluded. Prostacyclin release did not differ significantly between seeded and unseeded grafts and arteries, when the arteries were looked upon as one group. When the graft was compared with its corresponding artery, i.e. the artery it replaced, a significantly lower release was found in the unseeded group. Thromboxane release was undetectable in arteries but significantly higher in both graft groups. SEM revealed a cellular coverage of 75% in the seeded grafts and 50% in the unseeded (not significant). Light microscopy showed a patchy staining for Factor VIII-related antigen in some grafts in both groups. CONCLUSION: Prostacyclin release in unseeded and seeded dacron grafts did not differ 3 months after implantation in sheep, except when the graft was compared with its corresponding artery. The significance of this remains to be settled. Seeded grafts did not have a higher proportion of endothelial coverage than unseeded grafts.
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