| 1. |
- Björling, Marcus
(författare)
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Friction in elasto hydrodynamically lubricated contacts : the influence of speed and slide to roll ratio
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Reducing losses in transmissions has become a high priority in the automotive market during recent years, mainly due to environmental concerns leading to regulations placed on the automotive industry to drive the development of vehicles with lower fuel consumption and CO2 emissions. Rising fuel prices and increasing environmental concerns have also made customers more prone to purchase more fuel efficient vehicles. In addition to the fuel savings that could be achieved by increased efficiency of transmissions there are other benefits as well. A more efficient transmission will in general generate less heat, and experience less wear. This will lead to fewer failures, longer service life of components, and possibly longer service intervals. Furthermore this implies a possibility to reduce coolant components, thus reducing the total weight of the system, leading to a further decrease in consumption and a lower impact on the environment due to a reduction of material usage. A low weight design is also beneficial for vehicle dynamics and handling. In addition to the automotive market, gears are extensively used in many other fields, such as wind power and industry. In some cases a substantial part of the losses in a gear transmission is attributed to gear contact friction due to sliding and rolling between the gear teeth. To better understand the contact friction phenomena in gears an experimental apparatus capable of running under similar conditions to gears is chosen. By using a ball on disc test device the contact friction can be measured in a broad range of speeds and slide to roll ratios (SRR). The results are presented as a 3D friction map which can be divided into four different regions; Linear, Non-linear, mixed and thermal. In each of these regions different mechanisms are influencing the coefficient of friction. Several tests have been conducted with different lubricants, EP- additive packages, operating temperatures, surface roughness and coatings. The method gives a good overview, a system fingerprint, of the frictional behaviour for a specific system in a broad operating range. By observing results for different systems, it is possible to identify how different changes will influence the coefficient of friction in different regimes, and therefore optimize the system depending on operating conditions. Among other things the tests have shown that reducing base oil viscosity increases contact friction in most operating conditions, introducing an earlier transition from full film to mixed lubrication, and increasing full film friction in many cases with high sliding speeds. An increase in operating temperature could both increase, and decrease the coefficient of friction depending on running conditions. Introducing smoother surfaces reduces the coefficient of friction at lower entrainment speeds since thinner lubricant films are required to avoid asperity collitions. By applying a DLC coating on one or both surfaces in a EHL contact, the friction coefficient is shown to decrease, even in the full film regime.
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| 2. |
- Crona, Mikael, et al.
(författare)
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A Rare Combination of Ribonucleotide Reductases in the Social Amoeba Dictyostelium discoideum
- 2013
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Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 288:12, s. 8198-8208
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Tidskriftsartikel (refereegranskat)abstract
- Ribonucleotide reductases (RNRs) catalyze the only pathway for de novo synthesis of deoxyribonucleotides needed for DNA replication and repair. The vast majority of eukaryotes encodes only a class I RNR, but interestingly some eukaryotes, including the social amoeba Dictyostelium discoideum, encode both a class I and a class II RNR. The amino acid sequence of the D. discoideum class I RNR is similar to other eukaryotic RNRs, whereas that of its class II RNR is most similar to the monomeric class II RNRs found in Lactobacillus spp. and a few other bacteria. Here we report the first study of RNRs in a eukaryotic organism that encodes class I and class II RNRs. Both classes of RNR genes were expressed in D. discoideum cells, although the class I transcripts were more abundant and strongly enriched during mid-development compared with the class II transcript. The quaternary structure, allosteric regulation, and properties of the diiron-oxo/radical cofactor of D. discoideum class I RNR are similar to those of the mammalian RNRs. Inhibition of D. discoideum class I RNR by hydroxyurea resulted in a 90% reduction in spore formation and decreased the germination viability of the surviving spores by 75%. Class II RNR could not compensate for class I inhibition during development, and an excess of vitamin B12 coenzyme, which is essential for class II activity, did not improve spore formation. We suggest that class I is the principal RNR during D. discoideum development and growth and is important for spore formation, possibly by providing dNTPs for mitochondrial replication.
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| 3. |
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| 4. |
- Fagerqvist, Therese, et al.
(författare)
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Off-pathway alpha-synuclein oligomers seem to alter alpha-synuclein turnover in a cell model but lack seeding capability in vivo
- 2013
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Ingår i: Amyloid. - : Informa UK Limited. - 1350-6129 .- 1744-2818. ; 20:4, s. 233-244
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Tidskriftsartikel (refereegranskat)abstract
- Aggregated α-synuclein is the major component of Lewy bodies, protein inclusions observed in the brain in neurodegenerative disorders such as Parkinson’s disease and dementia with Lewy bodies. Experimental evidence indicates that α-synuclein potentially can be transferred between cells and act as a seed to accelerate the aggregation process. Here, we investigated in vitro and in vivo seeding effects of α-synuclein oligomers induced by the reactive aldehyde 4-oxo-2-nonenal (ONE). As measured by a Thioflavin-T based fibrillization assay, there was an earlier onset of aggregation when α-synuclein oligomers were added to monomeric α-synuclein. In contrast, exogenously added α-synuclein oligomers did not induce aggregation in a cell model. However, cells overexpressing α-synuclein that were treated with the oligomers displayed reduced α-synuclein levels, indicating that internalized oligomers either decreased the expression or accelerated the degradation of transfected α-synuclein. Also in vivo there were no clear seeding effects, as intracerebral injections of α-synuclein oligomers into the neocortex of α-synuclein transgenic mice did not induce formation of Proteinase K resistant α-synuclein pathology. Taken together, we could observe a seeding effect of the ONE-induced α-synuclein oligomers in a fibrillization assay, but neither in a cell nor in a mouse model.
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| 5. |
- Fagerqvist, Therese, et al.
(författare)
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Off-pathway α-synuclein oligomers seem to alter α-synuclein turnover in a cell model but lack seeding capability in vivo
- 2013
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Ingår i: Amyloid. - : Informa Healthcare. - 1350-6129 .- 1744-2818. ; 20:4, s. 233-244
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Tidskriftsartikel (refereegranskat)abstract
- Aggregated alpha-synuclein is the major component of Lewy bodies, protein inclusions observed in the brain in neurodegenerative disorders such as Parkinson's disease and dementia with Lewy bodies. Experimental evidence indicates that alpha-synuclein potentially can be transferred between cells and act as a seed to accelerate the aggregation process. Here, we investigated in vitro and in vivo seeding effects of alpha-synuclein oligomers induced by the reactive aldehyde 4-oxo-2-nonenal (ONE). As measured by a Thioflavin-T based fibrillization assay, there was an earlier onset of aggregation when alpha-synuclein oligomers were added to monomeric alpha-synuclein. In contrast, exogenously added alpha-synuclein oligomers did not induce aggregation in a cell model. However, cells overexpressing alpha-synuclein that were treated with the oligomers displayed reduced alpha-synuclein levels, indicating that internalized oligomers either decreased the expression or accelerated the degradation of transfected alpha-synuclein. Also in vivo there were no clear seeding effects, as intracerebral injections of alpha-synuclein oligomers into the neocortex of alpha-synuclein transgenic mice did not induce formation of proteinase K resistant alpha-synuclein pathology. Taken together, we could observe a seeding effect of the ONE-induced alpha-synuclein oligomers in a fibrillization assay, but neither in a cell nor in a mouse model.
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| 6. |
- Nystedt, Björn, et al.
(författare)
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The Norway spruce genome sequence and conifer genome evolution
- 2013
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 497:7451, s. 579-584
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Tidskriftsartikel (refereegranskat)abstract
- Conifers have dominated forests for more than 200 million years and are of huge ecological and economic importance. Here we present the draft assembly of the 20-gigabase genome of Norway spruce (Picea abies), the first available for any gymnosperm. The number of well-supported genes (28,354) is similar to the >100 times smaller genome of Arabidopsis thaliana, and there is no evidence of a recent whole-genome duplication in the gymnosperm lineage. Instead, the large genome size seems to result from the slow and steady accumulation of a diverse set of long-terminal repeat transposable elements, possibly owing to the lack of an efficient elimination mechanism. Comparative sequencing of Pinus sylvestris, Abies sibirica, Juniperus communis, Taxus baccata and Gnetum gnemon reveals that the transposable element diversity is shared among extant conifers. Expression of 24-nucleotide small RNAs, previously implicated in transposable element silencing, is tissue-specific and much lower than in other plants. We further identify numerous long (>10,000 base pairs) introns, gene-like fragments, uncharacterized long non-coding RNAs and short RNAs. This opens up new genomic avenues for conifer forestry and breeding.
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| 7. |
- Oliw, Ernst H., 1948-, et al.
(författare)
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Manganese lipoxygenase oxidizes bis-allylic hydroperoxides and octadecenoic acids by different mechanisms
- 2011
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Ingår i: Biochimica et Biophysica Acta - Molecular and Cell Biology of Lipids. - : Elsevier BV. - 1388-1981 .- 1879-2618. ; 1811:3, s. 138-147
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Tidskriftsartikel (refereegranskat)abstract
- Manganese lipoxygenase (MnLOX) oxidizes (11R)-hydroperoxylinolenic acid (11R-HpOTrE) to a peroxyl radical. Our aim was to compare the enzymatic oxidation of 11R-HpOTrE and octadecenoic acids with LOO-H and allylic C-H bond dissociation enthalpies of ~88 and ~87kcal/mol. Mn(III)LOX oxidized (11Z)-, (12Z)-, and (13Z)-18:1 to hydroperoxides with R configuration, but this occurred at insignificant rates (<1%) compared to 11R-HpOTrE. We next examined whether transitional metals could mimic this oxidation. Ce(4+) and Mn(3+) transformed 11R-HpOTrE to hydroperoxides at C-9 and C-13 via oxidation to a peroxyl radical at C-11, whereas Fe(3+) was a poor catalyst. Our results suggest that MnLOX oxidizes bis-allylic hydroperoxides to peroxyl radicals in analogy with Ce(4+) and Mn(3+). The enzymatic oxidation likely occurs by proton-coupled electron transfer of the electron from the hydroperoxide anion to Mn(III) and H(+) to the catalytic base, Mn(III)OH(-). Hydroperoxides abolish the kinetic lag times of MnLOX and FeLOX by oxidation of their metal centers, but 11R-HpOTrE was isomerized by MnLOX to (13R)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoic acid (13R-HpOTrE) with a kinetic lag time. This lag time could be explained by two competing transformations, dehydration of 11R-HpOTrE to 11-ketolinolenic acid and oxidation of 11R-HpOTrE to peroxyl radical; the reaction rate then increases as 13R-HpOTrE oxidizes MnLOX with subsequent formation of two epoxyalcohols. We conclude that oxidation of octadecenoic acids and bis-allylic hydroperoxides occurs by different mechanisms, which likely reflect the nature of the hydrogen bonds, steric factors, and the redox potential of the Mn(III) center.
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| 8. |
- Sahlin, Fredrik, et al.
(författare)
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A mixed lubrication model incorporating measured surface topography. Part 1: Theory of flow factors
- 2010
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 224:4, s. 335-351
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Tidskriftsartikel (refereegranskat)abstract
- A mixed lubrication model that permits real three-dimensional surface topography as input is developed. The theory of computing flow factors within the model is presented, and with a following paper (Part 2) the method of measuring and adapting the surface roughness, and model validation through flow measurements and application to a bearing is shown. A contact mechanics model is used to calculate the elastoplastic displacement of a periodic topography signal. A method based on homogenization is used to calculate flow factors for all lubrication regimes. The flow factors are compared with the Patir and Cheng method. Results indicate that the two methods compare well for longitudinal roughness lay, but differ significantly for a cross-patterned surface roughness due to the more complete flow description of the current model.
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| 9. |
- Sahlin, Fredrik, et al.
(författare)
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A mixed lubrication model incorporating measured surface topography. Part 2: Roughness treatment, model validation, and simulation
- 2010
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Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - 1350-6501 .- 2041-305X. ; 224:4, s. 353-365
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Tidskriftsartikel (refereegranskat)abstract
- A mixed lubrication flow factor model that permits real three-dimensional surface topography as input has been developed. Part 1 gives the theory of computing flow factors within the model. In this article, a method of adapting the measured surface topography signal to suit the numerical models is developed and presented in detail. The mixed lubrication model is validated through flow measurements for three different rough surface test specimens. Simulation of a hydrodynamic bearing was conducted and the results are presented in terms of pressure distributions and Stribeck curves covering all lubrication regimes. The results indicate that the model may be an efficient and accurate engineering design and research tool for tribological devices operating in all lubrication regimes.
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| 10. |
- Valham, Fredrik, 1972-, et al.
(författare)
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Ambient temperature and obstructive sleep apnea : effects on sleep, sleep apnea and morning alertness
- 2012
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Ingår i: Sleep. - Westchester : American Academy of Sleep Medicine. - 0161-8105 .- 1550-9109. ; 35:4, s. 513-517
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Tidskriftsartikel (refereegranskat)abstract
- Study Objectives: The aim of the study was to investigate the effect of ambient temperature on sleep, sleep apnea, and morning alertness in patients with obstructive sleep apnea. Design: Randomized controlled trial. Setting: In-hospital investigations. Participants: Forty patients with obstructive sleep apnea naive to treatment, with an apnea-hypopnea index of 10-30. Interventions: Three different nights in room temperatures of 16 degrees C, 20 degrees C, and 24 degrees C. Measurements: Overnight polysomnography and Karolinska Sleepiness Scale. Results: The obstructive apnea-hypopnea index was 30 +/- 17 at 16 degrees C room temperature, 28 +/- 17 at 20 degrees C, and 24 +/- 18 at 24 degrees C. The obstructive apnea-hypopnea index was higher at 16 degrees C room temperature versus 24 degrees C (P = 0.001) and at 20 degrees C room temperature versus 24 degrees C (P = 0.033). Total sleep time was a mean of 30 min longer (P = 0.009), mean sleep efficiency was higher (77 +/- 11% versus 71 +/- 13% respectively, P = 0.012), and the patients were significantly more alert according to the Karolinska Sleepiness Scale (P < 0.028) in the morning at 16 degrees C room temperature versus 24 degrees C. The amount of sleep in different sleep stages was not affected by room temperature. Conclusions: Untreated patients with obstructive sleep apnea sleep longer, have better sleep efficiency, and are more alert in the morning after a night's sleep at 16 degrees C room temperature compared with 24 degrees C, but obstructive sleep apnea is more severe at 16 degrees C and 20 degrees C compared with 24 degrees C.
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