| 1. |
- Teng, Penghua, 1987-, et al.
(författare)
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Numerical Modelling of Incipient Motion of Fracture Infillings
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Fine-grained infilling materials in rock fractures cannot be penetrated by cement-based grout, while high water velocities in the unfilled parts of the fracture can impose erosion of the infilling materials. Understanding the erosion process of the infilling materials is, therefore, essential for the design of grout curtains. In this paper, the incipient motion of infilling particles in a three-dimensional rock fracture is predicted by a coupled Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) approach. A fracture model is built based on high-resolution optical scanning data of a natural rock joint surface. Infilling particles are modelled as non-cohesive spheric particles in a range of fine-sand sizes. The motion of particles is produced by coupling the CFD, solving the Navier-Stokes equations, with the DEM, prescribing the contact forces between particles. The model could capture the particle-particle and particle-fluid interaction behaviours during particle movement. Simulation results of the fracture model are compared with a parallel-plate model, which shows that the fracture geometry significantly affects the transport and distribution of the infillings. The dimensionless critical shear stress of the fracture model for the studied fracture is 11% larger than the values obtained from the parallel-plate model. Furthermore, the simulations are compared with the Hjulström and Shields diagrams, showing that the use of these two diagrams to predict the infilling erosion in the fracture results in a significant discrepancy. In contrast, a previous equation derived from flume experiments under laminar flows agrees better with the simulations. The present study visualises and quantitatively analyses the erosion process of the fracture infillings, which provides a reference to predict the threshold of the infilling erosion.
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| 2. |
- Teng, Penghua, 1987-, et al.
(författare)
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Numerical modelling of incipient motion of fracture infillings
- 2021
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- Fine-grained infilling materials in rock fractures cannot be penetrated by cement-based grout, while high water velocities in the unfilled parts of the fracture can impose erosion of the infilling materials. Understanding the erosion process of the infilling materials is, therefore, essential for the design of grout curtains. In this paper, the incipient motion of infilling particles in a three-dimensional rock fracture is predicted by a coupled Computational Fluid Dynamics (CFD)-Discrete Element Method (DEM) approach. A fracture model is built based on highresolution optical scanning data of a natural rock joint surface. Infilling particles are modelled as non-cohesive spheric particles in a range of fine-sand sizes. The motion of particles is produced by coupling the CFD, solving the Navier-Stokes equations, with the DEM, prescribing the contact forces between particles. The model could capture the particle-particle and particle-fluid interaction behaviours during particle movement. Simulation results of the fracture model are compared with a parallel-plate model, which shows that the fracture geometry significantly affects the transport and distribution of the infillings. The dimensionless critical shear stress of the fracture model for the studied fracture is 11% larger than the values obtained from the parallel-plate model. Furthermore, the simulations are compared with the Hjulstro center dot m and Shields diagrams, showing that the use of these two diagrams to predict the infilling erosion in the fracture results in a significant discrepancy. In contrast, a previous equation derived from flume experiments under laminar flows agrees better with the simulations. The present study visualises and quantitatively analyses the erosion process of the fracture infillings, which provides a reference to predict the threshold of the infilling erosion.
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| 3. |
- Yang, James, adj prof, et al.
(författare)
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Experiments and CFD modeling of high-velocity two-phase flows in a large chute aerator facility
- 2019
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - : HONG KONG POLYTECHNIC UNIV, DEPT CIVIL & STRUCTURAL ENG. - 1994-2060 .- 1997-003X. ; 13:1, s. 48-66
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Forskningsöversikt (refereegranskat)abstract
- Mathematical formulations of two-phase flows at an aerator remain a challenging issue for spillway design. Due to their complexities in terms of water-air interactions subjected to high flow velocities, experiments play an essential role in evaluations of numerical models. The paper focuses on the underlying influence of the air-water momentum exchange in the two-phase Two-Fluid Model. It is modified to better represent the drag force acting on a group of air bubbles and the wall lubrication force accounting for near-wall phase interactions. Based on data from a large aerator rig with an approach velocity of 14.3 m/s, the models are evaluated for calculations of entrained air characteristics of a flow mixture. The air bubble diameter used in the modeling ranges from 0.5 to 4 mm as suggested by the experiments. In terms of air cavity configurations and aerator air demand, smaller air bubbles lead to better agreement with the test results. As far as air concentrations are concerned, the modified model gains by comparison. In the air cavity zone, smaller bubble sizes also provide better matches with the experiments. However, the near-base air concentration remains overestimated downstream from the impact area. The fact that the program user must pre-define a single air bubble size in simulations presumably limits the correct reproduction of near-base air concentrations and of their decay.
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| 4. |
- Zhang, Penghua, et al.
(författare)
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Engineering BspQI nicking enzymes and application of N.BspQI in DNA labeling and production of single-strand DNA
- 2010
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Ingår i: Protein Expression and Purification. - : Elsevier BV. - 1046-5928. ; 69:2, s. 226-234
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Tidskriftsartikel (refereegranskat)abstract
- BspQI is a thermostable Type IIS restriction endonuclease (REase) with the recognition sequence 5′GCTCTTC N1/N4 3′. Here we report the cloning and expression of the bspQIR gene for the BspQI restriction enzyme in Escherichia coli. Alanine scanning of the BspQI charged residues identified a number of DNA nicking variants. After sampling combinations of different amino acid substitutions, an Nt.BspQI triple mutant (E172A/E248A/E255K) was constructed with predominantly top-strand DNA nicking activity. Furthermore, a triple mutant of BspQI (Nb.BspQI, N235A/K331A/R428A) was engineered to create a bottom-strand nicking enzyme. In addition, we demonstrated the application of Nt.BspQI in optical mapping of single DNA molecules. Nt or Nb.BspQI-nicked dsDNA can be further digested by E. coli exonuclease III to create ssDNA for downstream applications. BspQI contains two potential catalytic sites: a top-strand catalytic site (Ct) with a D-H-N-K motif found in the HNH endonuclease family and a bottom-strand catalytic site (Cb) with three scattered Glu residues. BlastP analysis of proteins in GenBank indicated a putative restriction enzyme with significant amino acid sequence identity to BspQI from the sequenced bacterial genome Croceibacter atlanticus HTCC2559. This restriction gene was amplified by PCR and cloned into a T7 expression vector. Restriction mapping and run-off DNA sequencing of digested products from the partially purified enzyme indicated that it is an EarI isoschizomer with 6-bp recognition, which we named CatHI (CTCTTC N1/N4).
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| 5. |
- Zhang, Zhenwen, et al.
(författare)
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Central Administration of Galanin Receptor 1 Agonist Boosted Insulin Sensitivity in Adipose Cells of Diabetic Rats
- 2016
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Ingår i: Journal of Diabetes Research. - : Hindawi Limited. - 2314-6745 .- 2314-6753.
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Tidskriftsartikel (refereegranskat)abstract
- Our previous studies testified the beneficial effect of central galanin on insulin sensitivity of type 2 diabetic rats. The aim of the study was further to investigate whether central M617, a galanin receptor 1 agonist, can benefit insulin sensitivity. The effects of intracerebroventricular administration of M617 on insulin sensitivity and insulin signaling were evaluated in adipose tissues of type 2 diabetic rats. The results showed that central injection of M617 significantly increased plasma adiponectin contents, glucose infusion rates in hyperinsulinemic-euglycemic clamp tests, GLUT4 mRNA expression levels, GLUT4 contents in plasma membranes, and total cell membranes of the adipose cells but reduced the plasma C-reactive protein concentration in nondiabetic and diabetic rats. The ratios of GLUT4 contents were higher in plasma membranes to total cell membranes in both nondiabetic and diabetic M617 groups than each control. In addition, the central administration of M617 enhanced the ratios of pAkt/Akt and pAS160/AS160, but not phosphorylative cAMP response element-binding protein (pCREB)/CREB in the adipose cells of nondiabetic and diabetic rats. These results suggest that excitation of central galanin receptor 1 facilitates insulin sensitivity via activation of the Akt/AS160 signaling pathway in the fat cells of type 2 diabetic rats.
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