| 51. |
- Choquet, Isabelle, 1965-, et al.
(författare)
-
New powder port holder geometry to avoid lump formation in APS
- 2005
-
Ingår i: 17th international symposium on plasma chemistry (ISPC 17). ; , s. OP7. 1-6
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A new geometry of the powder port ring holder used in atmospheric plasma spraying has recently been designed to avoid lump formation, and successfully tested for a set of process parameters associated with Ni-5Al powder used in production to form bond coat [1]. But with ZrO 2 powder used to made top coat, improvements were not enough satisfactory. Here, we investigate numerically the cause of the remaining defects, and further improve the ring geometry to prevent lump from forming in any part of the coating.
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| 52. |
- Crawford, Tim, et al.
(författare)
-
Specific functions for Mediator complex subunits from different modules in the transcriptional response of Arabidopsis thaliana to abiotic stress
- 2020
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
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| 53. |
- Curry, Nicholas, et al.
(författare)
-
Performance Testing of Suspension Plasma Sprayed Thermal Barrier Coatings Produced with Varied Suspension Parameters
- 2015
-
Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 5:3, s. 338-356
-
Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spraying has become an emerging technology for the production of thermal barrier coatings for the gas turbine industry. Presently, though commercial systems for coating production are available, coatings remain in the development stage. Suitable suspension parameters for coating production remain an outstanding question and the influence of suspension properties on the final coatings is not well known. For this study, a number of suspensions were produced with varied solid loadings, powder size distributions and solvents. Suspensions were sprayed onto superalloy substrates coated with high velocity air fuel (HVAF) -sprayed bond coats. Plasma spray parameters were selected to generate columnar structures based on previous experiments and were maintained at constant to discover the influence of the suspension behavior on coating microstructures. Testing of the produced thermal barrier coating (TBC) systems has included thermal cyclic fatigue testing and thermal conductivity analysis. Pore size distribution has been characterized by mercury infiltration porosimetry. Results show a strong influence of suspension viscosity and surface tension on the microstructure of the produced coatings.
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| 54. |
- Davoine, Celine, et al.
(författare)
-
Functional metabolomics as a tool to analyze Mediator function and structure in plants
- 2017
-
Ingår i: PLOS ONE. - : Public Library Science. - 1932-6203. ; 12:6
-
Tidskriftsartikel (refereegranskat)abstract
- Mediator is a multiprotein transcriptional co-regulator complex composed of four modules; Head, Middle, Tail, and Kinase. It conveys signals from promoter-bound transcriptional regulators to RNA polymerase II and thus plays an essential role in eukaryotic gene regulation. We describe subunit localization and activities of Mediator in Arabidopsis through metabolome and transcriptome analyses from a set of Mediator mutants. Functional metabolomic analysis based on the metabolite profiles of Mediator mutants using multivariate statistical analysis and heat-map visualization shows that different subunit mutants display distinct metabolite profiles, which cluster according to the reported localization of the corresponding subunits in yeast. Based on these results, we suggest localization of previously unassigned plant Mediator subunits to specific modules. We also describe novel roles for individual subunits in development, and demonstrate changes in gene expression patterns and specific metabolite levels in med18 and med25, which can explain their phenotypes. We find that med18 displays levels of phytoalexins normally found in wild type plants only after exposure to pathogens. Our results indicate that different Mediator subunits are involved in specific signaling pathways that control developmental processes and tolerance to pathogen infections.
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| 55. |
- Ekberg, Johanna, 1987, et al.
(författare)
-
Analysis of single splats produced by axial suspension plasma spraying
- 2018
-
Ingår i: Surface Engineering. - : Informa UK Limited. - 1743-2944 .- 0267-0844. ; 35:5, s. 407-411
-
Tidskriftsartikel (refereegranskat)abstract
- Axial suspension plasma spraying (ASPS) is a relatively new, innovative technique with which microstructures have been produced that are similar to the ones produced by electron beam physical vapor deposition. They have a columnar structure and consist of nm- and µm-sized pores. However, so far the formation of the microstructure is not fully understood because fragmentation and vaporisation of the liquid significantly affects the deposition process. Analysis of single splats can provide important information on the phenomena controlling the coating formation process and the final coating properties. Therefore, the present study aims at providing first results of 8 wt-% yttria-stabilised zirconia single splats sprayed onto a steel substrate by use of ASPS. Scanning electron microscopy and atomic force microscopy have been used to characterise the splats with respect to appearance, shape, and size distribution.
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| 56. |
- Elfving, Nils, et al.
(författare)
-
A dynamic interplay of nucleosome and Msn2 binding regulates kinetics of gene activation and repression following stress
- 2014
-
Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 42:9, s. 5468-5482
-
Tidskriftsartikel (refereegranskat)abstract
- The transcription factor Msn2 mediates a significant proportion of the environmental stress response, in which a common cohort of genes changes expression in a stereotypic fashion upon exposure to any of a wide variety of stresses. We have applied genome-wide chromatin immunoprecipitation and nucleosome profiling to determine where Msn2 binds under stressful conditions and how that binding affects, and is affected by, nucleosome positioning. We concurrently determined the effect of Msn2 activity on gene expression following stress and demonstrated that Msn2 stimulates both activation and repression. We found that some genes responded to both intermittent and continuous Msn2 nuclear occupancy while others responded only to continuous occupancy. Finally, these studies document a dynamic interplay between nucleosomes and Msn2 such that nucleosomes can restrict access of Msn2 to its canonical binding sites while Msn2 can promote reposition, expulsion and recruitment of nucleosomes to alter gene expression. This interplay may allow the cell to discriminate between different types of stress signaling.
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| 57. |
- Elfving, Nils, 1982-
(författare)
-
Functional studies of Mediator in Arabidopsis thaliana and Saccharomyces cerevisiae
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mediator has been shown to be essential for regulation of RNA Polymerase II mediated transcription. Mediator functions as an interface between the general transcriptional machinery and a multitude of DNA binding transcriptional regulators, although the molecular mechanism for the process is elusive. Mediator is a large complex of over twenty subunits, most of which are conserved from yeast to plants to mammals. Many of these subunits are essential for viability in yeast, and mutations in the corresponding genes have global effects on transcription. Mediator was originally identified in Saccharomyces cerevisiae, but has since been described in most eukaryotes. However, until recently the Mediator complex was not identified in plants. This thesis describes the first successful identification and isolation of the Mediator complex from the plant Arabidopsis thaliana. By raising antibodies against candidate A. thaliana Mediator subunits, we were able to purify a multisubunit protein complex. Mass spectrometry and bioinformatics analysis allowed us to identify 21 of these subunits as conserved Mediator components and six as A. thaliana specific subunits. Some of the genes that encode the identified Mediator subunits had earlier been described as components of specific regulatory pathways controlling for example cell proliferation and flowering time. Subsequent genetic analysis confirmed that the A. thaliana Mediator complex is important for several plant signaling pathways, including flowering and stress pathways. This thesis also describes identification of regulators that interact with the A. thaliana Mediator subunit Med25, previously identified as PFT1 (Phytochrome and Flowering Time 1) and implicated in regulation of flowering time in response to light quality. Finally, we describe the function of Mediator in S. cerevisiae using genome-wide approaches. We have carried out a transcriptional switch where half of the genome changes expression and determined Mediator occupancy across the genome before and after such a switch, using ChIP-SEQ on tagged subunits from different Mediator domains. Unexpectedly, we find that Mediator occupancy is limited at most promoters. However, at the highly occupied promoters, we see different modes of changes in occupancy as a result of the transcriptional switch. These highly occupied promoters control genes involved in different stress response pathways. Thus, our results suggest that Mediator function and composition differ considerably between different promoters.
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| 58. |
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| 59. |
- Elfving, Nils, et al.
(författare)
-
The Arabidopsis thaliana Med25 mediator subunit integrates environmental cues to control plant development
- 2011
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:20, s. 8245-8250
-
Tidskriftsartikel (refereegranskat)abstract
- Development in plants is controlled by abiotic environmental cues such as day length, light quality, temperature, drought, and salinity. These signals are sensed by a variety of systems and transmitted by different signal transduction pathways. Ultimately, these pathways are integrated to control expression of specific target genes, which encode proteins that regulate development and differentiation. The molecular mechanisms for such integration have remained elusive. We here show that a linear 130-amino-acids-long sequence in the Med25 subunit of the Arabidopsis thaliana Mediator is a common target for the drought response element binding protein 2A, zinc finger homeodomain 1, and Myb-like transcription factors which are involved in different stress response pathways. In addition, our results show that Med25 together with drought response element binding protein 2A also function in repression of PhyB-mediated light signaling and thus integrate signals from different regulatory pathways.
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| 60. |
- Elofsson, Jessica
(författare)
-
Children’s early mathematics learning and development : Number game interventions and number line estimations
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Children’s early mathematics learning and development have become a topic of increasing interest over the past decade since early mathematical knowledge and skills have been shown to be a strong predictor of later mathematics performance. Understanding how children develop mathematical knowledge and skills and how they can be supported in their early learning could thus prove to be a vital component in promoting learning of more formal mathematics.In light of the above, with this thesis I sought to contribute to an increased understanding of children’s early mathematics learning and development by examining effects of playing different number games on children’s number knowledge and skills, and by investigating children’s representations of numbers on number line tasks.Two number game intervention studies were performed, and effects of three different number game conditions (linear number, circular number and nonlinear number) were investigated by examining 5- and 6-year-old children’s pre- and posttest performance on different numerical tasks. The findings indicate that playing number games in general support children’s development of number knowledge and skills, where the specific learning outcomes are affected differently depending on the type of number game utilized.To elucidate children’s representations of numbers, their performance on two different umber line tasks have been analyzed using a latent class modeling approach. The results reveal that there is a heterogeneity in 5- and 6-year-old children’s number line estimations and subgroups of children showing different estimation patterns were distinguished. In addition, it is shown that children’s number line estimations can be associated to their number knowledge as well as to task specific aspects.The findings presented in this thesis contribute to the discussion of the value of selecting game activities in a conscious way to support children’s early mathematics learning and development. They also add to the discussion regarding the number line task and how children’s number line estimations can be analyzed and interpreted.
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| 61. |
|
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| 62. |
- Everitt, Carl-Magnus, 1988-
(författare)
-
Initiation of rolling contact fatigue from asperities in elastohydrodynamic lubricated contacts
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly.In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line.In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.
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| 63. |
- Fallath, Thorya, et al.
(författare)
-
MEDIATOR18 and MEDIATOR20 confer susceptibility to Fusarium oxysporum in Arabidopsis thaliana
- 2017
-
Ingår i: PLOS ONE. - : PUBLIC LIBRARY SCIENCE. - 1932-6203. ; 12:4
-
Tidskriftsartikel (refereegranskat)abstract
- The conserved protein complex known as Mediator conveys transcriptional signals by acting as an intermediary between transcription factors and RNA polymerase II. As a result, Mediator subunits play multiple roles in regulating developmental as well as abiotic and biotic stress pathways. In this report we identify the head domain subunits MEDIATOR18 and MEDIATOR20 as important susceptibility factors for Fusarium oxysporum infection in Arabidopsis thaliana. Mutants of MED18 and MED20 display down-regulation of genes associated with jasmonate signaling and biosynthesis while up-regulation of salicylic acid associated pathogenesis related genes and reactive oxygen producing and scavenging genes. We propose that MED18 and MED20 form a sub-domain within Mediator that controls the balance of salicylic acid and jasmonate associated defense pathways.
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| 64. |
- Fefekos, Alexandros G., et al.
(författare)
-
Effect of spray angle and substrate material on formation mechanisms and properties of HVAF sprayed coatings
- 2023
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 452
-
Tidskriftsartikel (refereegranskat)abstract
- Thermally sprayed coatings are often used to enhance the surface properties (wear resistance, corrosion resistance, etc.) of engineering components in order to extend their performance and service lifetime. Typically, the industrial components to be coated possess complex geometries and are fabricated using different materials, which can influence the deposited coating’s microstructure and performance. High-velocity air fuel (HVAF) process is a relatively new thermal spray processing technique that has shown tremendous potential to deposit high performance coatings for durable industrial components. However, no detailed studies have been reported on HVAF sprayed coating formation mechanisms so far in relation to the spray angle and substrate properties, and the influence of coating material on the above. The objective of this work was to study the influence of spray angles and substrate materials on splat characteristics, coating microstructure evolution, properties and performance for two distinct coating materials. In this study, one cermet (WC-CoCr) and one metallic (Inconel 625) feedstock were deposited onto three different substrates (aluminium alloy, carbon steel and Hastelloy-X) utilising different spray angles (40°, 60° and 90°). The coating evolution was analysed utilising SEM/EDS, image analysis, and micro-indentation. To determine the tribological performance, coatings were subjected to dry sliding wear test utilising alumina ball as counter surface and specific wear rates were obtained. The results showed that initial splat characteristics were substantially altered on changing the substrate and the spray angle. However, the final coating properties were not affected significantly even though the deposition rate was reduced significantly at lower spray angle, suggesting the versatility of the HVAF process.
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| 65. |
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| 66. |
- Flanagan, John N., et al.
(författare)
-
Role of follistatin in promoting adipogenesis in women
- 2009
-
Ingår i: Journal of Clinical Endocrinology and Metabolism. - : The Endocrine Society. - 0021-972X .- 1945-7197. ; 94:8, s. 3003-9
-
Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: Follistatin is a glycoprotein that binds and neutralizes biological activities of TGFbeta superfamily members including activin and myostatin. We previously identified by expression profiling that follistatin levels in white adipose tissue (WAT) were regulated by obesity. OBJECTIVE: The objective of the study was to elucidate the role of follistatin in human WAT and obesity. DESIGN: We measured secreted follistatin protein from WAT biopsies and fat cells in vitro. We also quantified follistatin mRNA expression in sc and visceral WAT and in WAT-fractionated cells and related it to obesity status, body region, and cellular origin. We investigated the effects of follistatin on adipocyte differentiation of progenitor cells in vitro. PARTICIPANTS: Women (n = 66) with a wide variation in body mass index were recruited by advertisement and from a clinic for weight-reduction therapy. RESULTS: WAT secreted follistatin in vitro. Follistatin mRNA levels in sc but not visceral WAT were decreased in obesity and restored to nonobese levels after weight reduction. Follistatin mRNA levels were high in the stroma-vascular fraction of WAT and low in adipocytes. Recombinant follistatin treatment promoted adipogenic differentiation of progenitor cells and neutralized the inhibitory action of myostatin on differentiation in vitro. Moreover, activin and myostatin signaling receptors were detected in WAT and adipocytes. CONCLUSION: Follistatin is a new adipokine important for adipogenesis. Down-regulated WAT expression of follistatin in obesity may counteract adiposity but could, by inhibiting adipogenesis, contribute to hypertrophic obesity (large fat cells) and insulin resistance.
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| 67. |
- Frodelius, Jenny, et al.
(författare)
-
Ti2AlC coatings deposited by High Velocity Oxy-Fuel spraying
- 2008
-
Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 202:24, s. 5976-5981
-
Tidskriftsartikel (refereegranskat)abstract
- High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H2 and O2. A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti2AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3–5 GPa for the coatings sprayed with a powder size of 38 μm.
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| 68. |
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| 69. |
- Frost, Robert J. W., et al.
(författare)
-
Preliminary results from a study of luminescent materials : For application in the beam imaging system at the ESS
- 2023
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier. - 0168-583X .- 1872-9584. ; 540, s. 227-233
-
Tidskriftsartikel (refereegranskat)abstract
- As part of the development of the beam imaging system at the European Spallation Source, luminescent screens have been fabricated by the flame spraying of scintillating materials onto stainless steel backings. A total of seven screens were produced, three of chromia alumina (Al2O3:Cr), two of YAG (Y3Al5O12:Ce) and two of a 50/50 mix of these. The properties of these screens under proton irradiation were evaluated using a2.55 MeV proton beam at currents of up to 10 μA. Irradiation times were up to 25 h per sample, during which luminescence-, spectrographic-, thermal- and current-data was sampled at a rate of 1 Hz. Preliminary results of these measurements are reported here; with a quantitative analysis presented for one of the chromia alumina screens and a qualitative comparison of all three material types. The luminescent yield for chromia alumina was determined to be around 2000 photons/MeV for a virgin screen, and was found to drop to 1.5% after 167 mC of proton irradiation. A recovery of the luminescence of chromia alumina to >60% was observed after beam current was reduced for an 8 h period. Observations indicate that the YAG and mixed composition screens retain higher luminescence than the chromia alumina even at temperatures of over 200 ◦C. It is indicated that the luminescence from YAG feeds the R-lines of chromia alumina in the mixed composition screens.
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| 70. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
A Facile Approach to Deposit Graphenaceous Composite Coatings by Suspension Plasma Spraying
- 2019
-
Ingår i: Coatings. - : MDPI AG. - 2079-6412. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates, for the first time ever, the deposition of graphenaceous composite coatings using an easy, yet robust, suspension plasma spraying (SPS) process. As a case study, a composite coating comprising 8 wt.% of yttria-stabilized-zirconia (8YSZ) and reinforced with graphene oxide (GO) was deposited on a steel substrate. The coatings were sprayed using an 8YSZ-GO mixed suspension with varied plasma spray parameters. Establishing the possibility of retaining the graphene in a ceramic matrix using SPS was of specific interest. Electron microscopy and Raman spectroscopy confirmed the presence of graphenaceous material distributed throughout the coating in the 8YSZ matrix. The experimental results discussed in this work confirm that SPS is an immensely attractive pathway to incorporate a graphenaceous material into virtually any matrix material and can potentially have major implications in enabling the deposition of large-area graphene-containing coatings for diverse functional applications.
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| 71. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Characterization of Microstructure and Thermal Properties of YSZ Coatings Obtained by Axial Suspension Plasma Spraying (ASPS)
- 2015
-
Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 24:7, s. 1195-1204
-
Tidskriftsartikel (refereegranskat)abstract
- The paper aims at demonstrating various microstructures which can be obtained using the suspension spraying technique and their respective significance in enhancing the thermal insulation property of a thermal barrier coating. Three different types of coating microstructures are discussed which were produced by the Axial Suspension Plasma Spraying. Detailed characterization of coatings was then performed. Optical and scanning electron microscopy were utilized for microstructure evaluations; x-ray diffraction for phase analysis; water impregnation, image analysis, and mercury intrusion porosimetry for porosity analysis, and laser flash analysis for thermal diffusivity measurements were used. The results showed that Axial Suspension Plasma Spraying can generate vertically cracked, porous, and feathery columnar-type microstructures. Pore size distribution was found in micron, submicron, and nanometer range. Higher overall porosity, the lower density of vertical cracks or inter-column spacing, and higher inter-pass porosity favored thermal insulation property of the coating. Significant increase in thermal diffusivity and conductivity was found at higher temperature, which is believed to be due to the pore rearrangement (sintering and pore coarsening). Thermal conductivity values for these coatings were also compared with electron beam physical vapor deposition (EBPVD) thermal barrier coatings from the literature and found to be much lower. © 2015 ASM International
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| 72. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Novel utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings
- 2021
-
Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 295
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to axially inject liquid feedstock has encouraged the thermal spray research community to explore this concept to deposit coatings for various next generation functional applications. The current study explores the utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings for the first time. The study successfully demonstrates the use of a powder-suspension hybrid processing approach to incorporate a solid lubricant Boron Nitride (as suspension) in a wear resistant Cr3C2–NiCr (as powder) cermet matrix. Coatings were characterized using Scanning Electron Microscopy and Raman Spectroscopy to analyze their microstructure and phase constitution. The results show that the tribological performance of the hexagonal boron nitride (hBN)-incorporated composite coating was significantly better than the traditional powder-derived Cr3C2–NiCr coating. Such hBN-incorporated composite coatings are needed to improve the mechanical properties and enhance the overall tribological performance of metallic components used in various applications, especially at high temperature such as cylinder bore, pistons, deformation tools, etc. The limitations of liquid based lubricants at high temperature motivates the use of hBN reinforced composite coatings as it can form a protective solid lubrication tribo-film. The study concludes that the emerging HVAF technology can accommodate liquid feedstock and be successfully utilized to deposit hybrid powder-suspension composite coatings to create multi length scale microstructures which can be attractive for combining different tribological attributes in the same coatings system.
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| 73. |
- Ganvir, Ashish, 1991-, et al.
(författare)
-
Tribological performance assessment of Al2O3-YSZ composite coatings deposited by hybrid powder-suspension plasma spraying
- 2021
-
Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 409
-
Tidskriftsartikel (refereegranskat)abstract
- The advent of high-throughput plasma spray systems that allow axial feeding encourages the study of using liquid feedstock for various next-generation functional applications. The current study explores the benefit of such a plasma spray system to deposit hybrid powder-suspension Al2O3-YSZ ceramic matrix composite (CMC) coatings for tribological applications. The tribological performance of the hybrid processed CMC coatings was assessed using scratch, ball-on-plate wear and erosion tests and compared with that of monolithic powder-derived Al2O3 coatings. As-deposited and tribo-tested coatings were characterized using Scanning Electron Microscopy, X-ray Diffraction and Energy Dispersive Spectroscopy to analyse their microstructure and phase constitution. The results showed that the tribological performance of the hybrid powder-suspension Al2O3-YSZ CMC coating was significantly improved by enhancing the wear resistance under scratch, dry sliding ball-on-plate and erosion tests as compared to the conventional APS deposited monolithic Al2O3 coating. About 36% decrease in the dry sliding ball-on-plate specific wear rate and up to 50% decrease in the erosion wear rate was noted in the hybrid powder-suspension Al2O3-YSZ CMC coating as compared to the conventional APS deposited monolithic Al2O3 coating. The study concludes that the hybrid powder-suspension route can create CMC coatings with unique multi-length scale microstructures which can be attractive for combining different tribological attributes in the same coating system.
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| 74. |
- Goel, Sneha, 1993-, et al.
(författare)
-
Axial Plasma Spraying of Mixed Suspensions : A Case Study on Processing, Characteristics, and Tribological Behavior of Al2O3-YSZ Coatings
- 2020
-
Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 10:15
-
Tidskriftsartikel (refereegranskat)abstract
- Thermal spraying deploying liquid feedstock offers an exciting opportunity to obtain coatings with characteristics vastly different from those produced using conventional spray-grade powders. The most extensively investigated variant of this technique is Suspension Plasma Spraying (SPS), which utilizes a suspension of fine powders in an appropriate medium. The relatively recent advent of axial feed capable plasma spray systems can enable higher throughputs during SPS, provides the possibility for spraying with longer stand-off distances, and also permit the use of suspensions with higher solid loading. The present work investigates axial plasma sprayed coatings produced using a mixed suspension of fine (submicron or nano-sized) powders of Al(2)O(3)and YSZ as a case study. Deposition of the mixed suspension using axial injection plasma spraying, comprehensive evaluation of characteristics of the resulting coatings, and assessment of their tribological behavior were of particular interest. Evaluation of surface morphology, microstructure, and hardness of the coatings reveals that axial SPS of mixed suspensions provides an exciting pathway to realize finely structured multi-constituent coatings using suspensions with as high as 40 wt.% solid loading. The study of scratch, dry sliding wear, and erosion behavior also specifically shows that the addition of YSZ in the Al(2)O(3)matrix can improve the tribological properties of the coating.
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| 75. |
- Goel, Sneha, 1993-, et al.
(författare)
-
Axial suspension plasma spraying of Al2O3 coatings for superior tribological properties
- 2017
-
Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 315, s. 80-87
-
Tidskriftsartikel (refereegranskat)abstract
- Suspension plasma spray is a relatively new thermal spray technique which enables feeding of fine powder to produce advanced coatings for varied applications. This work investigates the difference in structure and performance of Al2O3 coatings manufactured using conventional micron-sized powder feedstock and a suspension of sub-micron to few micron sized powder. Axial injection was implemented for deposition in both cases. The effect of feedstock size and processing on the tribological performance of the two coatings was of specific interest. The coatings were characterized by Optical and Scanning Electron Microscopy, micro-hardness and scratch resistance testing, and their dry sliding wear performance evaluated. The suspension sprayed coatings yielded significantly higher scratch resistance, lower friction coefficient and reduced wear rate compared to conventional coatings. The improved tribological behaviour of the former is attributable to finer porosity, smaller splat sizes, and improved interlamellar bonding.
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| 76. |
- Goel, Sneha, et al.
(författare)
-
Deposition of Novel Composite Coatings by Suspension-Powder Hybrid Plasma Spraying
- 2016
-
Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-8
-
Konferensbidrag (refereegranskat)abstract
- Suspension Plasma Spray (SPS) is an emerging technique which overcomes the difficulties typically associated with feeding of fine (submicron or nano-sized) powders in conventional atmospheric plasma spraying (APS) to obtain superior coating properties for various engineering applications. The advent of plasma spray systems that allow axial injection of feedstock, which considerably improves thermal exchange between the plasma plume and the injected feedstock, has enabled substantial enhancement in deposition rates/efficiencies to make SPS techno-commercially exciting. The present study utilizes both the above advances in plasma spraying to demonstrate the ability to deposit novel coating architectures by sequential/simultaneous axial injection of both powder and a suspension feedstock. The results reveal that composite coatings uniquely combining the micron-size features arising from the spray-grade powder and the submicron or nano-sized features attributable to the suspension, can be conveniently realized using the above approach. Three different kinds of coating architectures were generated, namely layered, composite, and functionally graded. The sprayed coatings were extensively characterized for attributes such as surface morphology, microstructure, and composition particularly in the case of composite coatings.
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| 77. |
- Goel, Sneha, 1993-, et al.
(författare)
-
Hybrid powder-suspension Al2O3-ZrO2 coatings by axial plasma spraying : Processing, characteristics & tribological behaviour
- 2017
-
Ingår i: Proceedings of the International Thermal Spray Conference & Exposition. - New York : Curran Associates, Inc. - 9781510858220 ; , s. 374-379
-
Konferensbidrag (refereegranskat)abstract
- The ability of suspension plasma spraying (SPS) to overcome difficulties associated with feeding of fine (submicron or nano-sized) powders and achieve more refined microstructures than possible in atmospheric plasma spraying (APS) is well established. In recent times, the use of axial injection plasma spray systems has yielded substantial enhancement in deposition rates/efficiencies due to improved thermal exchange between the plasma plume and injected feedstock. The present paper describes utilization of both the above advances in plasma spraying to create various function-dependent coating architectures through simultaneous and/or sequential spraying of hybrid powder-suspension feedstock. A specific variant of such hybrid axial plasma spraying that enables deposition of composite coatings by simultaneous injection of a powder and a suspension is discussed in particular detail. Results obtained using an Al2O3-ZrO2 material system as a case study reveal that composite coatings combining the micron-size features arising from the spray-grade Al2O3 powder and submicron or nano-sized features attributable to the ZrO2 suspension can be conveniently realized. The surface morphology, microstructure, and composition of these coatings, as well as their tribological behaviour determined using scratch and ball-on-disc tests, are presented herein. The utility of this method to develop a wide array of composite coatings is also discussed.
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| 78. |
- Gonzalez-Martinez, Juan Francisco, et al.
(författare)
-
Humidity-induced phase transitions of surfactants embedded in latex coatings can drastically alter their water barrier and mechanical properties
- 2018
-
Ingår i: Polymers. - : MDPI. - 2073-4360. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Latex coatings are environmentally friendly i.e., they are formed from aqueous polymer dispersions, are cheap to produce and provide exceptional mechanical properties. Therefore, they are ubiquitous and can be found in a wide range of different applications such as paints and varnishes, pressure-sensitive adhesives, textiles, construction materials, paper coatings and inks. However, they also have weaknesses and their surfactant content is among them. Surfactants are often needed to stabilize polymer particles in the aqueous latex dispersions. These surfactants also form part of the coatings formed from these dispersions, and it is well-known that they can lower their performance. This work further explores this aspect and focuses on the role that embedded surfactant domains play in the response of latex coatings to humid environments. For this purpose, we made use of several experimental techniques where humidity control was implemented: quartz crystal microbalance with dissipation, atomic force microscopy and differential scanning calorimetry. By means of this multimethodological approach, we report that surfactants embedded in latex coatings can undergo humidity-induced transitions towards more hydrated and softer phases, and that this results in a drastic decrease of the mechanical and water barrier properties of the whole coatings. Subsequently, this work highlights the potential of taking into account the phase behavior of surfactants when choosing which ones to use in the synthesis of latex dispersions as this would help in predicting their performance under different environmental conditions.
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| 79. |
- Grevholm, Barbro, et al.
(författare)
-
Lära och undervisa matematik : från förskoleklass till åk 6
- 2012
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Lära och undervisa matematik - från förskoleklass till åk 6 är en grundbok i matematik och matematikämnets didaktik. Den vänder sig till lärarstuderande och till verksamma lärare som vill aktualisera sina kunskaper och ta del av den senaste forskningen samt sätta sig in i de nya kursplanerna och kunskapskraven i matematik.
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| 80. |
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| 81. |
- Hallberg, Magnus, et al.
(författare)
-
Functional and physical interactions within the middle domain of the yeast mediator
- 2006
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Ingår i: Molecular Genetics and Genomics. - : Springer Science and Business Media LLC. - 1617-4615 .- 1617-4623. ; 276:2, s. 197-210
-
Tidskriftsartikel (refereegranskat)abstract
- Med21 (Srb7) is a small essential subunit of the middle domain of the Mediator, which is conserved in all eukaryotes. It is thought to play an important role in both transcriptional activation and repression. In the yeast Saccharomyces cerevisiae, Med21 is known to interact both with the Mediator subunit Med6 and the global co-repressor Tup1. We have made a temperature-sensitive med21-ts mutant, which we used in a high copy number suppressor screen. We found ten yeast genes that can suppress the med21-ts mutation in high copy number. The three strongest suppressors were MED7 and MED10 (NUT2), which encode other Mediator subunits, and ASH1, which encodes a repressor of the HO gene. 2-Hybrid experiments confirmed multiple interactions between Med21, Med10, Med7 and Med4, and also revealed a Med21 self-interaction. The interactions of Med21 with Med7 and Med10 were verified by co-immunoprecipitation of tagged proteins produced in insect cells and E. coli, where both interactions were found to depend strongly on the amino acid residues 2-8 of Med21. These interactions, and the interactions of Med21 with Med6 and Tup1, suggest that Med21 may serve as a molecular switchboard that integrates different signals before they reach the core polymerase.
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| 82. |
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| 83. |
|
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| 84. |
- Hallberg, Magnus, 1974-
(författare)
-
Studies of Functional Interactions within Yeast Mediator and a Proposed Novel Mechanism for Regulation of Gene Expression
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The yeast Mediator complex is required for transcriptional regulation both in vivo and in vitro and the identification of similar complexes from metazoans indicates that its function is conserved through evolution. Mediator subunit composition and structure is well characterized both by biochemical, genetic and biophysical methods. In contrast, little is known about the mechanisms by which Mediator operates and how the complex is regulated. The aim of my thesis was to elucidate how Mediator functions at the molecular level and to investigate functional interactions within Mediator. It is possible to recruit RNA polymerase II to a target promoter and thus to activate transcription by fusing Mediator subunits to a DNA binding domain. In order to investigate functional interactions within Mediator, we made such fusion proteins where different Mediator subunits were fused to the DNA binding domain of lexA. The expression of a reporter gene containing binding sites for lexA was subsequently measured in both a wild type strain and in strains where genes encoding specific Mediator subunits had been disrupted. We found that lexA-Med2 and lexA-Gal11 are strong activators that function independently of all Mediator subunits tested. On the other hand, lexA-Srb10 is a weak activator that depends on Srb8 and Srb11 and lexA-Med1 and lexA-Srb7 are both cryptic activators that become active in the absence of Srb8, Srb10, Srb11, or Sin4. Both lexA-Med1 and lexA-Srb7 proteins showed a stable association with the Mediator subunits Med4 and Med8 in wild type cells and in all deletion strains tested, indicating that they were functionally incorporated into the Mediator complex. We also showed that both Med4 and Med8 exist in two forms that differed in electrophoretic mobility and that these forms differed in their ability to associate with Mediator immuno-purified from the LEXA-SRB7 and LEXA-MED1 strains. Dephosphorylation assays of purified Mediator indicated that the two mobility forms of Med4 corresponded to the phosphorylated and unphosphorylated forms of the Med4 protein respectively. Some of the data presented in this study as well as previous genetic and biochemical data obtained in our lab suggested a functional link between the Med1, Med2, Srb10 and Srb11 proteins. We extended these findings by showing that the Srb10 kinase phosphorylates the Med2 protein at residue serine 208, both in vitro and in vivo. We also showed that a point mutation of the single phosphorylation site to an alanine or to an aspartic acid residue altered the gene expression of a specific set of genes. Taken together, these data indicate that posttranslational modification of Mediator subunits is a so far uncharacterized mechanism for regulation of gene expression. In order to study the function of the Srb7 subunit of Mediator, we isolated a temperature sensitive strain where the amino acids 2 to 8 of srb7 were deleted. The Mediator subunits Nut2 and Med7 were isolated as high copy suppressor of srb7-∆(2-8) and we were also able to show that Srb7 interacted with Nut2 and Med7 both in a 2-hybrid system and in co-immuno precipitation experiments using recombinantly expressed proteins. Interestingly, a deletion of amino acids 2 to 8 of Srb7 abolishes its interaction with both Med7 and Nut2 in vitro. Med4 also interacted with Srb7 in the 2-hybrid system and surprisingly, the first eight amino acids of Srb7 were shown to be sufficient for this interaction.
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| 85. |
- Hameed, Pearlin, et al.
(författare)
-
Axial Suspension Plasma Spraying : An ultimate technique to tailor Ti6Al4V surface with HAp for orthopaedic applications
- 2019
-
Ingår i: Colloids and Surfaces B. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 173, s. 806-815
-
Tidskriftsartikel (refereegranskat)abstract
- Dissolution of atmospheric plasma sprayed (APS) hydroxyapatite (HAp) coatings on Ti-6Al-4 V medical implants have always been a challenge to overcome in the field of biomedical industry. In the present work, an attempt has been made to develop a HAp coating using a novel thermal spray process called axial suspension plasma spraying (SPS), which leads to thin adherent coatings. Two HAp coatings fabricated by APS (P1 and P2) and four SPS HAp coatings (S1, S2, S3 and S4) produced with varying spraying parameters were characterized in terms of (1) microstructure, porosity, hardness, adhesion strength, contact angle and phase purity; (2) corrosion resistance in 10% Fetal bovine serum (FBS); (3) in-vitro cell adherence and cell viability using human umbilical cord blood-derived mesenchymal stem cells (hMSCs). Amongst different APS and SPS coatings, P1 and S3 exhibited superior properties. S3 coating developed using SPS exhibited 1.3 times higher adhesion strength when compared to APS coating (P1) and 9.5 times higher corrosion resistance than P1. In addition, both S3 and P1 exhibited comparatively higher biocompatibility as evidenced by the presence of more than 92% viable hMSCs. © 2018 Elsevier B.V.
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| 86. |
- Henriksson, Robin, 1986-
(författare)
-
Secondary prevention after acute coronary syndrome : antiplatelet therapy and risk factor control
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: One of the leading causes of death and disability worldwide is cardiovascular disease (CVD), including acute myocardial infarction (AMI). Despite improvements in medical treatment, management, and care over the years and the halving of mortality in recent decades, there is considerable room for improvement. Following myocardial infarction (MI), a patient is at great risk for subsequent infarctions or other related complications. In addition, the risk of ischemic stroke is increased following MI. Secondary prevention after MI is paramount for reducing further complications and consists of lifestyle changes, optimised medical treatment, and risk factor control of blood pressure (BP) and blood lipid levels. Although secondary preventive measures are effective, the proportion of patients reaching set treatment target levels is disappointingly low.Most patients are prescribed dual antiplatelet therapy (DAPT) following MI as part of their secondary preventive treatment. Several articles have been published on treatment efficacy based on comparisons with different kinds of antiplatelet drugs and in different combinations. However, little data specifically address the incidence of ischemic stroke after MI in real-world populations. In addition to antiplatelet treatment, secondary prevention comprises risk factor control of hypertension and hyperlipidaemia. Given the low proportion of patients reaching set target levels for BP and blood lipids, new strategies are needed.Aims: The aim of this dissertation is partly to elucidate if the rapid change in preferred DAPT in Sweden, from clopidogrel to ticagrelor in addition to aspirin, affected the incidence of ischemic stroke in patients suffering AMI (paper I) and in patients suffering AMI who have a history of ischemic stroke (paper II).The second part of the dissertation aims to investigate the feasibility and implementation of a randomised controlled trial of a nurse-led telephone-based secondary preventive program, and to assess the proportion of patients who can be included in an unselected acute coronary syndrome (ACS) population (paper III). Furthermore, the aim of the trial was to assess the long term results regarding systolic BP (SBP), diastolic BP (DBP), and low-density lipoprotein cholesterol (LDL-C) after 36 months of intervention and follow-up compared to a control group receiving usual care (paper IV).Methods: Papers I and II examined the impact of a change in the antiplatelet regimen following MI in regard to ischemic stroke occurrence. Data were obtained from the Swedish Register of Information and Knowledge about Swedish Heart Intensive Care Admissions (i.e., RIKS-HIA). The register was combined with the National Patient Register (NPR) and the Cause of Death Register (CDR) in order to obtain data on stroke occurrence. Patients with AMI and treated with either clopidogrel or ticagrelor were assigned to one of two cohorts, each covering a 2- year time period, with the initial prescription of ticagrelor (20 Dec 2011) used as a cutoff point. Patients in the early cohort (n=23,447) were treated exclusively with clopidogrel, whereas those in the later cohort (n=24,227) were treated with either clopidogrel (47.9%) or ticagrelor (52.1%). In paper II, the same methodology was used, but with a study sample restricted to AMI patients with a history of ischemic stroke. In paper II, there were 1633 patients in the early cohort and 1642 in the late cohort. In the late cohort, 66.3% patients were treated with clopidogrel and 33.7% with ticagrelor. Kaplan–Meier analysis was used to assess the risk of ischemic stroke over time, with multivariable Cox regression analysis used to identify predictors of ischemic stroke. Nurse-based Age independent Intervention to Limit Evolution of Disease (Papers III and IV were based on the NAILED)-ACS trial. The NAILED-ACS trial was an open randomised controlled trial of whether a nurse-led telephone-based follow-up and medical titration after MI or unstable angina achieved lower levels of BP and LDL-C than usual care. In paper III, patients admitted for ACS during January 2010 and December 2013 were evaluated for participation. Factors predicting participation and non- participation were assessed using logistic regression. Mortality rates after one year among included and excluded patients and patients declining participation were assessed using Kaplan–Meier analysis. For paper IV, all patients admitted with ACS at Östersund Hospital between January 2010 and December 2014 were screened for inclusion based on their ability to participate in a telephone- based follow-up. Participants were randomised into two parallel groups, an intervention group and a control group receiving usual care. BP and LDL-C were measured at 1, 12, 24, and 36 months. The baseline consisted of randomised patients who completed the one-month follow-up. The intervention group received counselling and medical titration to attain treatment targets (BP <140/<90 mmHg and LDL-C <2.5/<1.8 mmol/L). Adjusted means stratified by sex and type of ACS were calculated for SBP and DBP and LDL-C. The proportion of patients who achieved treatment target levels at the end of the study was also assessed.Results: Among the general AMI population treated with either clopidogrel or ticagrelor, the incidence of ischemic stroke after one year was 2.8% in the early cohort vs. 2.4% in the late cohort (p=0.001) (paper I). The study population in paper II, in which all patients had a history of previous ischemic stroke, was overall older and had a higher prevalence of comorbidities than the population in paper I. In paper II, incidence of ischemic stroke in the early cohort was 12.1% vs. 8.6% in the late cohort (p<0.01). Corresponding incidence of intracranial bleeding for the population in paper II was a non-significant 1.2% vs 1.5%.In the feasibility study of the NAILED-ACS trial (paper III), 907 patients were assessed for inclusion. Among these, 72.9% could be included (n=661), 146 patients (16.1%) were excluded, and 100 patients declined participation (11 %). Reasons for exclusion were mainly participation in another trial, dementia, inability to use a telephone, and advanced disease. Examples of predictors of both exclusion and declining participation were older age, lower functional status, and lower education. Non-participating patients had significantly higher mortality rates at one year compared to participating patients.Paper IV presents the final results of the NAILED-ACS risk factor trial in which a total of 962 patients were randomised and completed the one-month follow- up. Of this group, 797 were available for analysis after 36 months. Compared to the control group, in the intervention group, mean SBP was 4.1 mmHg lower, mean DBP was 2.9 mmHg lower, and mean LDL-C was 0.28 mmol/L lower (p<0.001 for all). The proportions of patients reaching treatment target goals for SBP, DBP, and LDL-C were significantly higher in the intervention group. In regard to SBP, 77.6% of intervention patients achieved treatment target levels, compared to 62.9% in the control group. Corresponding numbers for DBP were 90.9% vs. 80.8% and for LDL-C, they were 65.6% vs. 53.1%Conclusion: The incidence of ischemic stroke was significantly lower in a cohort of AMI patients following a change in preferred treatment from clopidogrel to ticagrelor (paper I). In AMI patients with a history of ischemic stroke (paper II), the incidence rate of ischemic stroke was significantly lower in the late cohort compared to the early cohort, and overall incidence rates were markedly higher than in paper I.The NAILED-ACS trial was shown to be both feasible (paper III) and successful, with a higher proportion of patients reaching treatment target levels in the intervention group, and significantly lower mean values for SBP, DBP, and LDL- C (paper IV).
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| 87. |
- Holmberg, Hans-Christer, et al.
(författare)
-
Contribution of the legs to double-poling performance in elite cross-country skiers.
- 2006
-
Ingår i: Medicine and science in sports and exercise. - : Ovid Technologies (Wolters Kluwer Health). - 0195-9131 .- 1530-0315. ; 38:10, s. 1853-60
-
Tidskriftsartikel (refereegranskat)abstract
- In the classical style of cross-country skiing, the double-poling (DP) technique, which is regarded as an upper-body exercise, is used on the flatter parts of a course. Limited biomechanical and physiological data are available about DP compared with other cross-country skiing techniques. The purpose of the present study was to evaluate the possible role of the lower body during DP.Eleven elite cross-country skiers performed two incremental tests using DP roller skiing at 1 degree inclination on a treadmill with or without locking the knee and ankle joints (DPLOCKED and DPFREE). Maximal and peak oxygen uptake (VO2max and VO2peak) during classic diagonal skiing and DP, respectively, were measured. In addition, heart rate, blood lactate concentration, and maximal DP velocity (Vmax) were determined. Pole-ground reaction forces and joint angles (elbow, hip, knee, and ankle) were analyzed.The skiers obtained 7.7% higher VO2peak, 9.4% higher Vmax, and 11.7% longer time to exhaustion during DPFREE compared with DPLOCKED (all P < 0.05). There was a higher heart rate and blood lactate concentration in DPLOCKED at submaximal stages (all P < 0.05), with no difference in oxygen consumption. At 85% Vmax, corresponding to approximately 81% VO2peak FREE, the differences in physiological variables were accompanied by a 13.6% higher poling frequency, a 4.9% shorter poling phase, 13.3% shorter recovery phase, and 10.9% lower relative pole force in DPLOCKED (all P < 0.05).Movements of the knee and ankle joints are an integrative part in the skillful use of the DP technique, and restriction of the motion in these joints markedly affects both biomechanical and physiological variables, impairing DP performance.
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| 88. |
- Häggström, Daniel, et al.
(författare)
-
A Verified and Validated Model for Simulation-Driven Design of Heavy Duty Truck Synchronizers
- 2015
-
Ingår i: ASME Proceedings | ASME 2015 Power Transmission and Gearing Conference. - : ASME Press. - 9780791857205
-
Konferensbidrag (refereegranskat)abstract
- The strong market trend toward lower fuel consumption for heavy road transports requires more frequent gear shifting and increased gear shift performance, i.e. shorter shift time. Increased shift performance means higher loads for the synchronizer which brings component and shifting process optimization more into focus.Traditionally, synchronizer development has relied on physical testing of complete synchronizers in general gearbox test rigs or in specialized synchronization test rigs leaving much of the causes of the observed effects unclear. This paper presents a generalized FE-based thermomechanical simulation model to be used for model-based synchronizer analysis and design. The model is targeted for studies of how different external loads and the values of different synchronizer design parameters affect the temperature transient in the friction lining. Recommendations of how major modeling complications should be treated are presented. The developed simulation model is verified and validated with a combination of analytical means and transient temperature measurements of bulk and surface temperatures. The applicability of the presented model, as well as its limitations, are discussed and exemplified with different design cases.
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| 89. |
- Häggström, Daniel, et al.
(författare)
-
Evaluation of synchronizer loading parameters and their ability to predict failure
- 2018
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : Sage Publications. - 1350-6501 .- 2041-305X. ; 232:9, s. 1093-1104
-
Tidskriftsartikel (refereegranskat)abstract
- Molybdenum coated gearbox synchronizers are tested in a mu-comp test rig under varying loading conditions until failure. Four different parameters used to describe the thermomechanical load are evaluated just before failure to compare their ability to predict failure. The parameters evaluated are the synchronized kinetic energy, the synchronization power, and the focal as well as the average surface temperature increase. The focal surface temperature increase as well as the average surface temperature increase is found to predict failure with relatively good accuracy. It is shown that there exists a threshold which divides the synchronizer into either a very long or a very short service life. Additionally, a method to determine the average surface temperature in the gearbox management system is proposed.
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| 90. |
- Häggström, Daniel
(författare)
-
On synchronization of heavy truck transmissions
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gear shifts are becoming more and more important as engines are adapted to low speed high torque working conditions. Synchronizers are key components for successful gear shifts. To adapt the synchronizers to new working conditions due to adaptations to new engines, improved development tools are needed. The presented thesis describes the development of two types of numerical models for the synchronization process, namely fluid-structure interaction to simulate the pre-synchronization phase and thermomechanical FE models to simulate the main synchronization phase. A methodology for developing friction models based on a combination of physical testing and numerical simulations is presented. Additionally, a comprehensive gear shift and synchronizer frame of reference section is presented.In paper A, two numerical fluid-structure interaction simulation models for assessing the pre-synchronization phase are presented. Simulations show that the synchronizer functionality is highly dependent on the gear shift maneuvering system, and that grooves in the synchronizer surface have a positive effect on the oil evacuation during the pre-synchronization phase.Paper B describes the development of a numerical thermomechanical model for simulating the main synchronization phase. Two parameter studies were performed, one based on external loads and one based on synchronizer geometry. The effect on the temperature increase from differences in thermal properties between molybdenum and carbon friction linings are presented.In paper C, a verification and validation methodology for highly transient thermomechanical processes was presented. Numerical verification, bulk temperature measurement, surface temperature measurement and qualitative visual inspection were combined to verify and validate the simulation model presented in paper B.In paper D, a methodology combining physical testing with an thermomechanical simulation model to develop a friction model was exemplified by a molybdenum coated synchronizer. A simplified thermal model was developed to remove the dependence of full finite element thermal models. The friction models shows good agreement with measured data.
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| 91. |
- Häggström, Daniel, et al.
(författare)
-
Optimization of synchronizer cone angle with regard to manufacturing tolerances of cone roundness and cone angle
- 2020
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part D, journal of automobile engineering. - : SAGE PUBLICATIONS LTD. - 0954-4070 .- 2041-2991. ; 234:2-3, s. 681-688
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of manufacturing tolerances on the maximum focal temperature has been investigated by transient thermomechanical simulations. Both relative cone angle and cone out-of-roundness for molybdenum and carbon fibre reinforced polymer synchronizers were evaluated. It was shown that cone out-of-roundness significantly increases the focal contact temperature for that specific cone but has little impact on the opposing cone. Two populations of measured synchronizers were evaluated, and it was shown that the maximum focal surface temperature can be decreased in almost all tolerance cases by introducing a relative angle between the cones.
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| 92. |
- Häggström, Daniel, et al.
(författare)
-
Optimization of synchronizer cone angle with regards tomanufacturing tolerances of cone roundness and cone angle
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The effects from manufacturing tolerances on the maximum focal temperature has been investigated by transient thermomechanical simulations. Both relative cone angle and cone out-of-roundness for molybdenum and carbon fiber reinforced polymer (CFRP) synchronizers were evaluated. It was shown that cone out-of-roundness significantly increase the focal contact temperature for that specific cone, but has little impact on the opposing cone. Two populations of measured synchronizers were evaluated, and it was shown that the maximum focal surface temperature can be decreased in almost all tolerance cases by introducing a relative angle between the cones.
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| 93. |
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| 94. |
- Häggström, Daniel, et al.
(författare)
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Predicting friction in synchronizer systems
- 2016
-
Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 97, s. 89-96
-
Tidskriftsartikel (refereegranskat)abstract
- The coefficient of friction in synchronizers is important from both a performance and a functional point of view. The synchronization process is highly transient, and the parameters affecting the coefficient of friction have strong mutual dependences, making analysis highly complex. A new friction model for a lubricated molybdenum-steel contact has been developed based on integrating results from physical rig tests and FEM simulations. A simplified thermal model has also been developed, with the purpose to quickly assess the coefficient of friction based on transient force and synchronizer dimensions. The results show good correlation with measured data except at very low sliding speed.
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| 95. |
- Häggström, Daniel, et al.
(författare)
-
Robust pre-synchronization in heavy truck transmissions
- 2014
-
Ingår i: International Gear Conference 2014. - : Woodhead Publishing Limited. - 9781782421955 - 9781782421948 ; , s. 914-923
-
Konferensbidrag (refereegranskat)abstract
- Transmission performance directly influences vehicle behaviour, energy efficiency, and perceived quality. A modern transmission is an aggregate of interacting sub-systems, e. g. gears, bearings, synchronisers and other shifting elements. New transmission trends ask for increased shift performance with higher loads for the synchronising components. Synchroniser development has traditionally required exhaustive physical testing and few analytical methods exist. A numerical method for assessing pre-synchronisation performance, using a multi-physics FEM software, is presented. Simulations show that grooves in the synchroniser surface have a positive effect on pre-synchronisation, and that the presence of grooves seems to be more important than the groove design.
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| 96. |
- Häggström, Daniel, et al.
(författare)
-
The effect of manufacturing tolerances on the thermomechanical load of gearbox synchronizers
- 2018
-
Ingår i: Procedia CIRP. - : Elsevier. - 2212-8271.
-
Konferensbidrag (refereegranskat)abstract
- Transmission performance is crucial for heavy trucks and connected vehicles in general and for platooning of trucks in particular. Gearbox synchronizers are highly loaded conical friction brakes used during gear shifts. Service life and, thus, the gear shifting reliability, of the synchronizer depend on the local thermomechanical loading of the contact surface. To achieve a robust and cost-efficient system, more knowledge is needed of how manufacturing tolerances affect the local thermomechanical loading and therefore service life and reliability of a synchronizer. The effects from angle deviations between the mating cones and cone out-of-roundness on focal maximum temperature during a synchronization sequence have been studied with transient thermomechanical simulations. It is shown that thermomechanical effects will significantly magnify the nominal effects on synchronization performance caused by shape deviations given by the specified manufacturing tolerances.
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| 97. |
- Häggström, Daniel, et al.
(författare)
-
Thermomechanical performance of carbon fiber reinforced polymer synchronizer friction liners
- 2022
-
Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 236:6, s. 1074-1080
-
Tidskriftsartikel (refereegranskat)abstract
- To improve the ability of a thermomechanical simulation model for carbon fiber reinforced polymer lined synchronizers to predict synchronization performance and reliability, temperature dependent material data for the specific carbon fiber reinforced polymer lining is needed. The compressive modulus, coefficient of thermal expansion, specific heat and thermal conductivity are determined experimentally. The effect of each material property on the focal surface temperature is analyzed, and it is shown that the compressive modulus has the largest influence for all analyzed load cases. Physical tests show that surface hot spots begin to appear at a simulated focal surface temperature of 200 (Formula presented.) C, while performance degradation occurs at a simulated focal surface temperature of 230 (Formula presented.) C–250 (Formula presented.) C.
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| 98. |
- Häggström, Daniel, et al.
(författare)
-
Thermomechanical performance of CFRP synchronizer friction liners
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- To improve the ability of a thermomechanical simulation model for CFRP lined synchronizers to predict synchronization performance and reliability, temperature dependent material data for the specific CFRP lining is needed. The compressive modulus, coefficient of thermal expansion, specific heat and thermal conductivity are determined experimentally. The effect of each material property on the focal surface temperature is analyzed, and it is shown that the compressive modulus has the largest influence for all analyzed load cases. Physical tests show that surface hot spots begin to appear at a simulated focal surface temperature of 200 °C, while performance degradation occurs at a simulated focal surface temperature of 230 °C-250 °C.
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| 99. |
- Iwnicki, Simon, et al.
(författare)
-
Wheel-rail contact mechanics
- 2009
-
Ingår i: Wheel-rail interface handbook. - Cambridge, UK : Woodhead Publishing Ltd. - 9781845694128 - 9781845696788 - 9781439801468 ; , s. 58-92
-
Bokkapitel (refereegranskat)
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| 100. |
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