| 1. |
- Anderberg, Cecilia, et al.
(författare)
-
Wear Resistance of Smooth Automotive Cylinder Liner Surfaces
- 2005
-
Ingår i: World Tribology Congress III, Volume 2. - New York, NY : ASME Press. - 0791842029 ; , s. 603-604
-
Konferensbidrag (refereegranskat)abstract
- Demands for decreased environmental impact from vehicles are resulting in a strong push for decreased engine oil, fuel consumption and weight. New machining and coating technologies have offered ways to attack these problems. Engine oil and fuel consumption are to a great extent controlled by the topography of the cylinder liner surface and it is therefore important to optimise this surface. Recent engine tests have shown a reduction in oil consumption when using cylinder liners with a smoother finish than that given by the current plateau honing. However, engine manufacturers are hesitant to introduce smoother liner surfaces because of fears of severe wear and scuffing. There is also the possibility that smoother liner surfaces may be more sensitive to the choice of piston ring finishes. This paper therefore seeks to investigate the functional performance and resistance to wear of these smooth cylinder liners and the mating top ring surfaces. Copyright © 2005 by ASME
|
|
| 2. |
- Bergström, Tobias, et al.
(författare)
-
Developmentally regulated collagen/integrin interactions confer adhesive properties to early postnatal neural stem cells
- 2014
-
Ingår i: Biochimica et Biophysica Acta - General Subjects. - : Elsevier BV. - 0304-4165 .- 1872-8006. ; 1840:8, s. 2526-2532
-
Tidskriftsartikel (refereegranskat)abstract
- Background:It is becoming increasingly apparent that the extracellular matrix acts as an important regulator of the neural stem niche. Previously we found that neural stem and progenitor cells (NSPCs) derived from the early postnatal subventricular zone of mice adhere to a collagen/hyaluronan hydrogel, whereas NSPCs from the adult and embryonic brain do not.Methods:To examine the specific adhesive properties of young stem cells in more detail, NSPCs isolated from embryonic, postnatal day 6 (P6), and adult mouse brains were cultured on collagen I.Results:Early postnatal NSPCs formed paxillin-positive focal adhesions on collagen I, and these adhesions could be prevented by an antibody that blocked integrin beta 1. Furthermore, we found the corresponding integrin alpha subunits alpha 2 and alpha 11 levels to be highest at the postnatal stage. Gene ontology analysis of differentially expressed genes showed higher expression of transcripts involved in vasculature development and morphogenesis in P6 stem cells, compared to adult.Conclusions:The ability to interact with the extracellular matrix differs between postnatal and adult NSPCs.General significance:Our observations that the specific adhesive properties of early postnatal NSPCs, which are lost in the adult brain, can be ascribed to the integrin subunits expressed by the former furthering our understanding of the developing neurogenic niche. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.
|
|
| 3. |
- Bergström, Tobias, 1980-
(författare)
-
Modeling Neural Stem Cell and Glioma Biology
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on neural stem cell (NSC) and glioma biology. I discuss how NSCs interact with extracellular matrix (ECM) proteins in the stem cell niche, and investigate the consequences of deregulated Platelet-derived growth factor (PDGF) signaling for embryonic NSCs in transgenic mice. Furthermore I present cell cultures of human glioblastoma multiforme (GBM) that models human disease, taking into account the heterogeneity of GBM. Finally, interactions between brain tumors and mast cells are studied using the glioma cultures.In paper I, the importance of NSC interactions with the ECM in the stem cell niche during development is discussed. Contacts between NSCs and the ECM in the subventricular zone (SVZ) are emerging as important regulatory mechanisms. We show that early postnatal neural stem and progenitor cells (NSPC) attach to collagen I, and that the adhesion is explained by higher expression of collagen receptor integrins compared to adult NSPC. Further, blood vessels in the SVZ express collagen I, indicating a possible functional relationship.Growth factors, e.g. PDGF, regulate NSC proliferation and differentiation. Aberrant activation of growth factor signaling pathways also plays a role in brain tumor formation. Paper II demonstrates that transgenic mice expressing PDGF-B at high levels in embryonic NSCs displayed mild neurological defects but no hyperplasia or brain tumors. This suggests that a high level of PDGF is not sufficient to induce brain tumors from NSCs without further mutations.Paper III presents a novel panel of human glioma stem cell (GSC) lines from GBM that display NSC markers in vitro and form secondary orthotopic tumors in vivo. GBM has recently been categorized in molecular subclasses and we demonstrate, for the first time, that these subclasses can be retained in vitro by stem cell culture conditions. We have thus generated models for research and drug development aiming at a focused treatment depending on GBM subtype.Interactions with the immune system are integral parts of tumorigenesis. Mast cells are found in glioma and in paper IV we demonstrate that the grade-dependent infiltration of mast cells is in part mediated by macrophage migration inhibitory factor and phosphorylation of STAT5.
|
|
| 4. |
|
|
| 5. |
- Johansson, Staffan, et al.
(författare)
-
A Novel Approach to Reduction of Frictional Losses in a Heavy-Duty Diesel Engine by Reducing the Hydrodynamic Frictional Losses
- 2017
-
Ingår i: Advances in Tribology. - New York : Hindawi Publishing Corporation. - 1687-5915 .- 1687-5923. ; 2017, s. 1-17
-
Tidskriftsartikel (refereegranskat)abstract
- An important parameter in the reduction of fuel consumption of heavy-duty diesel engines is the Power Cylinder Unit (PCU); the PCU is the single largest contributor to engine frictional losses. Much attention, from both academia and industry, has been paid to reducing the frictional losses of the PCU in the boundary and mixed lubrication regime. However, previous studies have shown that a large portion of frictional losses in the PCU occur in the hydrodynamic lubrication regime. A novel texturing design with large types of surface features was experimentally analyzed using a tribometer setup. The experimental result shows a significant reduction of friction loss for the textured surfaces. Additionally, the textured surface did not exhibit wear. On the contrary, it was shown that the textured surfaces exhibited a smaller amount of abrasive scratches on the plateaus (compared to the reference plateau honed surface) due to entrapment of wear particles within the textures. The decrease in hydrodynamic friction for the textured surfaces relates to the relative increase of oil film thickness within the textures. A tentative example is given which describes a method of decreasing hydrodynamic frictional losses in the full-scale application. © 2017 Staffan Johansson et al.
|
|
| 6. |
- Johansson, Staffan, et al.
(författare)
-
Experimental friction evaluation of cylinder liner/piston ring contact
- 2011
-
Ingår i: Wear. - Amsterdam : Elsevier. - 0043-1648 .- 1873-2577. ; 271:3-4, s. 625-633
-
Tidskriftsartikel (refereegranskat)abstract
- Fuel consumption is an extremely important parameter for the automotive industry today. Anticipated emission legislative demands in combination with a rising oil price are true motivators. In engines the piston system is the largest source of frictional losses, accounting for about 50% of the total frictional losses, thus it is important to optimize. Apart from frictional losses the piston system is a large consumer of lubricating oil, a considerable contributor to the total amount of particulate emissions (PM). New materials, coatings and high-tech machining processes that previously were considered to be too expensive and therefore only used in complex applications are today becoming more affordable. It is important to develop reliable test methods to study these new concepts. The reciprocating tribometer at Volvo Technology has been updated to better evaluate the frictional difference between material combinations/surfaces; it is possible to evaluate a number of operational parameters in each experiment. The components that were studied were a piston ring running against a cylinder liner. Friction, wear and change in surface morphology were studied in the experiments. It is shown that for the introduced DoE based tribometer test the interaction of dynamic viscosity, velocity and contact pressure can be studied within one experiment. The results show differences in friction which could be explained as the surface creating beneficial contact conditions for oil film build-up. It is also apparent that surface roughness is important regardless of material properties. To better understand the correlations between friction and surface roughness a future study should include a study of similar materials with different roughness values.
|
|
| 7. |
|
|
| 8. |
- Johansson, Staffan G., et al.
(författare)
-
Optimization of the cylinder liner surface for reduction of oil consumption
- 2005
-
Ingår i: Proceedings of the World Tribology Congress III. - 0791842029 - 9780791842027 ; , s. 559-560
-
Konferensbidrag (refereegranskat)abstract
- A decrease of oil consumption in the modern truck engine would mean decrease of particulate matter and hydrocarbon emissions. This decrease has a positive impact on the environment. One important source of oil consumption is the piston/piston-ring/liner system. One way of decreasing oil consumption is to optimize the surface topography of the liner. In this study different liner surfaces and different piston rings were investigated. The investigation shows that it is possible to decrease both the oil film thickness and the friction without sacrificing wear properties of the piston-liner system. A new surface parameter for quick wear estimation of this system is presented. Copyright © 2005 by ASME.
|
|
| 9. |
- Johansson, Staffan, 1976, et al.
(författare)
-
Mechanistic Proposal for the Formation of Specific Immunogenic Complexes via a Radical Pathway: A Key Step in Allergic Contact Dermatitis to Olefinic Hydroperoxides
- 2009
-
Ingår i: Chem. Res. Toxicol.. - : American Chemical Society (ACS). - 0893-228X .- 1520-5010. ; 22:11, s. 1774-1781
-
Tidskriftsartikel (refereegranskat)abstract
- The widespread use of scented products causes an increase of allergic contact dermatitis to fragrance compounds in Western countries today. Many fragrance compounds are prone to autoxidation, forming hydroperoxides as their primary oxidation products. Hydroperoxides are known to be strong allergens and to form specific immunogenic complexes. However, the mechanisms for the formation of the immunogenic complexes are largely unknown. We have investigated this mechanism for (5R)-5-isopropenyl-2-methyl-2-cyclohexene-1-hydroperoxide (Lim-2-OOH) by studying the formation of adducts in the reaction between this hydroperoxide and 5,10,15,20-tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)TPPCl) in the presence of protected cysteine (NAc-Cys-OMe) or glutathione (GSH). Isolated adducts originate from the addition of the thiol group of NAc-Cys-OMe over the carbon−carbon double bonds of carvone. Furthermore, adducts between NAc-Cys-OMe and carveol as well as between GSH and carvone have been identified. The formation of these adducts most likely proceeds via the radical thiol−ene mechanism. The addition of a terpene moiety to cysteine offers an explanation of the specificity of the immune response to structurally different hydroperoxides. These results also explain the lack of cross-reactivity between carvone and Lim-2-OOH. In conclusion, we propose that immunogenic complexes of olefinic hydroperoxides can be formed via the radical thiol−ene mechanism. These complexes will be specific for the individual olefinic hydroperoxides due to the inclusion of a terpene moiety derived from the hydroperoxide.
|
|
| 10. |
- Johansson, Staffan, et al.
(författare)
-
New cylinder liner surfaces for low oil consumption
- 2008
-
Ingår i: Tribology International. - Oxford : Elsevier. - 0301-679X .- 1879-2464. ; 41:9-10, s. 854-859
-
Tidskriftsartikel (refereegranskat)abstract
- Anticipated emission legislation and reduced fuel consumption are the main driving forces when developing new engines. Optimization of the active surfaces in the piston system is one possible way to meet the above demands. In this study the effects of surface topography and texture direction of the ring/liner contact on oil film thickness and friction were simulated and experimentally tested. "Low wear" results from the experimental wear tests with "glide honed" smooth liner surfaces supported the "low friction" simulation results. In addition a new wear volume sensitive surface roughness parameter, Rktot, based on the Abbot-Firestone bearing area curve was introduced.
|
|
