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- Andersson, M., et al.
(författare)
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Coupling of lattice boltzmann and volume of fluid approaches to study the droplet behavior at the gas diffusion layer/gas channel interface
- 2018. - 13
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607688600 ; 86, s. 329-336
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Konferensbidrag (refereegranskat)abstract
- A typical polymer electrolyte fuel cell (PEFC) flow field consists of micro/minichannels. The continues removal of liquid water from the cathode channels is a critical topic, as water droplets forming in the channels may block the transport of gaseous oxygen to the active sites, which not only gives an uneven current distribution and substantial loss of performance, but also, increases degradation rates and unstable operation. Water generated by the electrochemical reactions condenses, depending on temperature mainly, into liquid form, potentially flooding various part of the PEFC. The aim of this work is to obtain an increased understanding of the droplet behavior at the gas diffusion layer (GDL) interface with the gas channels in PEFCs by the coupling of Lattice Boltzmann (LB) and Volume of Fluid (VOF) approaches. A multiscale environment is established with input parameters in the VOF model being extracted from in-house LB calculations. It is clear that the contact angle as well as the size of the liquid droplet vary with positions at the GDL surface, depending on the stochastic GDL geometry. A VOF model describing one straight channel with one gas inlet, one liquid inlet (at the GDL surface) and one two-phase outlet is employed.
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- Zhang, Shidong, et al.
(författare)
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Simple and complex polymer electrolyte fuel cell stack models : A comparison
- 2018. - 13
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. - 9781607685395 ; 86, s. 287-300
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Konferensbidrag (refereegranskat)abstract
- In this paper, two distinct polymer electrolyte fuel cell stack models are constructed: a detailed numerical model (DNM) employing a fine-scale computational mesh and a coarse-mesh approach based on a distributed resistance analogy (DRA) where diffusion terms in the transport equations are replaced by rate terms. Both methods are applied to a 5-cell, high-temperature polymer electrolyte fuel cell stack with an active area of 200 cm2 per cell. The polarization curve and local current density distributions from both the DRA and DNM are compared with experimental data, finding good agreement. Temperature, pressure, Nernst potential, and species distributions are also exhibited. The DNM displays details of fine-scale local extrema not captured by the DRA; however, the latter requires orders of magnitude less computer processor power and memory for execution. Both methods provide much finer-scale results than present experimental techniques.
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- Haga, K., et al.
(författare)
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Genetic Manipulation of Human Intestinal Enteroids Demonstrates the Necessity of a Functional Fucosyltransferase 2 Gene for Secretor-Dependent Human Norovirus Infection
- 2020
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Ingår i: mBio. - 2150-7511. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- Human noroviruses (HuNoVs) are the leading cause of nonbacterial gastroenteritis worldwide. Histo-blood group antigen (HBGA) expression is an important susceptibility factor for HuNoV infection based on controlled human infection models and epidemiologic studies that show an association of secretor status with infection caused by several genotypes. The fucosyltransferase 2 gene (FUT2) affects HBGA expression in intestinal epithelial cells; secretors express a functional FUT2 enzyme, while nonsecretors lack this enzyme and are highly resistant to infection and gastroenteritis caused by many HuNoV strains. These epidemiologic associations are confirmed by infections in stem cell-derived human intestinal enteroid (HIE) cultures. GII.4 HuNoV does not replicate in HIE cultures derived from nonsecretor individuals, while HIEs from secretors are permissive to infection. However, whether FUT2 expression alone is critical for infection remains unproven, since routinely used secretor-positive transformed cell lines are resistant to HuNoV replication. To evaluate the role of FUT2 in HuNoV replication, we used CRISPR or overexpression to genetically manipulate FUT2 gene function to produce isogenic HIE lines with or without FUT2 expression. We show that FUT2 expression alone affects both HuNoV binding to the HIE cell surface and susceptibility to HuNoV infection. These findings indicate that initial binding to a molecule(s) glycosylated by FUT2 is critical for HuNoV infection and that the HuNoV receptor is present in nonsecretor HIEs. In addition to HuNoV studies, these isogenic HIE lines will be useful tools to study other enteric microbes where infection and/or disease outcome is associated with secretor status. IMPORTANCE Several studies have demonstrated that secretor status is associated with susceptibility to human norovirus (HuNoV) infection; however, previous reports found that FUT2 expression is not sufficient to allow infection with HuNoV in a variety of continuous laboratory cell lines. Which cellular factor(s) regulates susceptibility to HuNoV infection remains unknown. We used genetic manipulation of HIE cultures to show that secretor status determined by FUT2 gene expression is necessary and sufficient to support HuNoV replication based on analyses of isogenic lines that lack or express FUT2. Fucosylation of HBGAs is critical for initial binding and for modification of another putative receptor(s) in HIEs needed for virus uptake or uncoating and necessary for successful infection by GII and several GII HuNoV strains.
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- Lata, K. Ramani, et al.
(författare)
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Investigation of the hyperfine properties of deoxy hemoglobin based on its electronic structure obtained by Hartree-Fock-Roothan procedure
- 2008
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Ingår i: Hyperfine Interactions. - : Springer Science and Business Media LLC. - 0304-3843 .- 1572-9540. ; 181:1-3, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the heme unit of deoxyhemoglobin including the proximal imidazole has been studied using the first-principles Hartree-Fock procedure. Our results for the Fe-57m isomer shift and asymmetry parameter are in very good agreement with the values obtained from Mossbauer spectroscopy measurements. The Fe-57m nuclear quadrupole coupling constant is smaller than the experimental result and possible ways to improve the agreement in the future are discussed. Improved analysis of the Mossbauer data, removing some approximations made for deriving the magnetic hyperfine tensor for the Fe-57m nucleus, is suggested to allow quantitative comparison with our results in the future.
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- Ramani-Mohan, R. -K, et al.
(författare)
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Deformation strain is the main physical driver for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation
- 2018
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Ingår i: Journal of Tissue Engineering and Regenerative Medicine. - : John Wiley and Sons Ltd. - 1932-6254 .- 1932-7005. ; 12:3, s. e1474-e1479
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Tidskriftsartikel (refereegranskat)abstract
- Mesenchymal stem cells play a major role during bone remodelling and are thus of high interest for tissue engineering and regenerative medicine applications. Mechanical stimuli, that is, deformation strain and interstitial fluid-flow-induced shear stress, promote osteogenic lineage commitment. However, the predominant physical stimulus that drives early osteogenic cell maturation is not clearly identified. The evaluation of each stimulus is challenging, as deformation and fluid-flow-induced shear stress interdepend. In this study, we developed a bioreactor that was used to culture mesenchymal stem cells harbouring a strain-responsive AP-1 luciferase reporter construct, on porous scaffolds. In addition to the reporter, mineralization and vitality of the cells was investigated by alizarin red staining and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Quantification of the expression of genes associated to bone regeneration and bone remodelling was used to confirm alizarin red measurements. Controlled perfusion and deformation of the 3-dimensional scaffold facilitated the alteration of the expression of osteogenic markers, luciferase activity, and calcification. To isolate the specific impact of scaffold deformation, a computational model was developed to derive a perfusion flow profile that results in dynamic shear stress conditions present in periodically loaded scaffolds. In comparison to actually deformed scaffolds, a lower expression of all measured readout parameters indicated that deformation strain is the predominant stimulus for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation.
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