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- Brodin, Håkan, 1969-
(författare)
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Failure of thermal barrier coatings under thermal and mechanical fatigue loading : microstructural observations and modelling aspects
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industrial and air-borne gas turbine hot components suffer from creep, oxidation, corrosion and microstructural degradation if not shielded from the hot and aggressive combustion gases. Two major strategies commercially available are adopted; film cooling by pressurised air and application of protective coatings. Protective coatings form a slow-growing oxide that protects from oxidation and corrosion. By application of a thermal insulator, a thermal barrier coating, the material will be protected from high temperature through good insulation properties of the coating system.If thermal barrier coatings are to be used in situations where capabilities and possibilities for inspections are limited, better knowledge of the fatigue properties of the coatings is also needed. Therefore development of a reliable fatigue life model is needed. The present work aims at serving as a basis from which a general physically founded thermal barrier coating life model can be formulated. The effects of exposure to high temperatures and mechanical loads on thermal barrier coatings under service like conditions have been investigated in the present thesis. Emphasis is put on the coupling between materials science and solid mechanics approaches in order to establish a better knowledge concerning degradation mechanisms and fatigue life issues than what is common if only one discipline is explored.Investigations of material exposed to isothermal oxidation and thermal cyclic fatigue were performed on plasma-sprayed systems with NiCoCrAIY or NiCrAIY bond coats and yttria partially stabilised zirconia top coats. It has been shown that the thermally grown oxide that will form upon high temperature exposure influences the failure behaviour. If the oxide is composed mainly of alumina, the fatigue properties are good since the adhesion between the ceramic top coat and the metallic bond coat is good. This is also shown in a comparison between different plasma sprayed thermal barrier coating systems. If the oxide formed is based on alurnina and spinel is avoided the fatigue properties benefit from a relatively flat interface where out-of plane stresses are low in comparison to a rough interface between top- and bond coat. These findings indicate that the bonding in air-plasma sprayed systems is dependent on so called chemical bonding if the thermally grown oxide is not voluminous with high growth stresses.It is possible to establish a fatigue life model for thermal barrier coatings. This has been shown with a model based on a modified Paris law formulation. The formulation needs to be modified with regards to mode rnixity of growth. Results achieved in the present project show that it is possible to extract crack growth data for interfacial crack growth. However a combination of mechanical testing and finite element modelling is needed since the load situation in critical areas cannot be measured. Crack growth results are presented and crack growth data are compared to predictions with good agreement.
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- Karlsson, M, et al.
(författare)
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Electroinjection of colloid particles and biopolymers into single unilamellar liposomes and cells for bioanalytical applications
- 2000
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Ingår i: Analytical Chemistry. - Univ Gothenburg, Dept Chem, SE-41296 Gothenburg, Sweden. Univ Gothenburg, Dept Chem Phys, SE-41345 Gothenburg, Sweden. : AMER CHEMICAL SOC. - 0003-2700 .- 1520-6882. ; 72:23, s. 5857-5862
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Tidskriftsartikel (refereegranskat)abstract
- A combined electroporation and pressure-driven microinjection method for efficient loading of biopolymers and colloidal particles into single-cell-sized unilamellar liposomes was developed. Single liposomes were positioned between a similar to2-mum tip diameter solute-filled glass micropipet, equipped with a Pt electrode, and a 5-mum-diameter carbon fiber electrode. A transient, 1-10 ms, rectangular waveform de voltage pulse (10-40 V/cm) was applied between the electrodes, thus focusing the electric field over the liposome. Dielectric membrane breakdown induced by the applied voltage pulse caused the micropipet tip to enter the liposome and a small volume (typically 50-500 x 10(-15) L) of fluorescein, YOYO-intercalated T7-phage DNA, 100-nm-diameter unilamellar liposomes, or fluorescent latex spheres could be injected into the intraliposomal compartment. We also demonstrate initiation of a chemical intercalation reaction between T2-phage DNA and YOYO-1 by dual injection into a single giant unilamellar liposome. The method was also successfully applied for loading of single cultured cells.
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- Li, Suling, et al.
(författare)
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Cytokine-induced Src homology 2 protein (CIS) promotes T cell receptor-mediated proliferation and prolongs survival of activated T cells.
- 2000
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 1540-9538 .- 0022-1007. ; 191:6, s. 985-994
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Tidskriftsartikel (refereegranskat)abstract
- Members of the suppressor of cytokine signaling (SOCS) family were discovered as negative regulators of cytokine signaling by inhibition of the Janus kinase–signal transducer and activator of transcription (Jak-STAT) pathway. Among them, cytokine-induced Src homology 2 (SH2) protein (CIS) was found to inhibit the interleukin 3– and erythropietin-mediated STAT5 signaling pathway. However, involvement of SOCS proteins in other signaling pathways is still unknown. This study shows that the expression of CIS is selectively induced in T cells after T cell receptor (TCR) stimulation. In transgenic mice, with selective expression of CIS in CD4 T cells, elevated CIS strongly promotes TCR-mediated proliferation and cytokine production in vitro, and superantigen-induced T cell activation in vivo. Forced expression of CIS also prolongs survival of CD4 T cells after TCR activation. Molecular events immediately downstream from the TCR are not changed in CIS-expressing CD4 T cells, but activation of mitogen-activated protein (MAP) kinase pathways by TCR stimulation is significantly enhanced. Together with the increased MAP kinase activation, a direct interaction of CIS and protein kinase Cθ was also demonstrated. These results suggest that CIS is one of the important regulators of TCR-mediated T cell activation. The functions of CIS, enhancing TCR signaling and inhibiting cytokine signaling, may be important in the regulation of immune response and homeostasis.
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- Strömberg, Anette, et al.
(författare)
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Microfluidic device for combinatorial fusion of liposomes and cells
- 2001
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Ingår i: Analytical Chemistry. - Gothenburg Univ, Dept Chem, S-41296 Gothenburg, Sweden. : AMER CHEMICAL SOC. - 0003-2700 .- 1520-6882. ; 73:1, s. 126-130
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Tidskriftsartikel (refereegranskat)abstract
- We describe an electrofusion-based technique for combinatorial synthesis of individual liposomes. A prototype device with containers for liposomes of different compositions and a fusion container was constructed. The sample containers had fluid contact with the fusion container through microchannels. Optical trapping was used to transport individual liposomes and cells through the microchannels into the fusion container. In the fusion container, selected pairs of liposomes were fused together using microelectrodes. A large number of combinatorially synthesized Liposomes with complex compositions and reaction systems can be obtained from small sets of precursor liposomes. The order of different reaction steps can be specified and defined by the fusion sequence. This device could also facilitate single cell-cell electrofusions (hybridoma production). This is exemplified by fusion of transported red blood cells.
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