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Jan Troost - One of the best experts on this subject based on the ideXlab platform.

  • The AdS3 boundary energy–momentum tensor, exact in the string length over the Curvature Radius
    Physics Letters B, 2010
    Co-Authors: Jan Troost
    Abstract:

    Abstract We clarify the map between boundary perturbations of AdS 3 in general relativity, and exactly marginal worldsheet vertex operators in AdS 3 string theory with Neveu–Schwarz Neveu–Schwarz flux. The latter correspond to solutions of the higher derivative low-energy tree level effective action to all orders in the string length over the Curvature Radius. We calculate the exact expression of the boundary energy–momentum tensor including all these higher derivative corrections in a purely bosonic string theory. The bottom-line is a canonical shift in the normalization of the boundary energy–momentum tensor corresponding to a shift in the Curvature Radius over the string length squared by the dual Coxeter number of the SL ( 2 , R ) subalgebra of the space–time Virasoro algebra. That allows us to propose a value for the Brown–Henneaux central charge including all tree level higher derivative corrections in bosonic string theory, in a scheme dictated by the worldsheet conformal field theory.

  • The AdS3 boundary energy momentum tensor, exact in the string length over the Curvature Radius
    Physics Letters B, 2010
    Co-Authors: Jan Troost
    Abstract:

    We first clarify the relation between boundary perturbations of AdS3 in general relativity, and exactly marginal worldsheet vertex operators in AdS3 string theory with Neveu-Schwarz Neveu-Schwarz flux. The latter correspond to solutions of the higher derivative low-energy tree level effective action to all orders in the string length over the Curvature Radius. We then calculate the exact expression of the boundary energy momentum tensor including all these higher derivative corrections in a purely bosonic string theory. The bottom-line is a canonical shift in the normalization of the boundary energy-momentum tensor corresponding to a shift in the Curvature Radius over the string length squared by the dual Coxeter number of the SL(2,R) subalgebra of the space-time Virasoro algebra. That allows us to derive the value of the Brown-Henneaux central charge including all tree level higher derivative corrections in bosonic string theory, in a scheme dictated by the worldsheet conformal field theory.

Dalu Gao - One of the best experts on this subject based on the ideXlab platform.

  • Effect of weld Curvature Radius and tool rotation direction on joint microstructure in friction stir welding casting alloys
    Materials & Design, 2014
    Co-Authors: Qian Yang, Zhihan Zhang, Dalu Gao
    Abstract:

    Abstract Curved welds were designed and the effects of the weld Curvature Radius and tool rotation direction on the microstructure of friction stir welded cast aluminum alloy joints were investigated. Results show that both the weld Curvature Radius and tool rotation direction have a significant influence on the microstructure of the curved joints during FSW. With decreasing weld Curvature Radius, the size of the tunnel defect is reduces and the proportion of fine Si particles in the stir zone increases. Si particles are finer and denser in the retreating side (RS) than that in the advancing side (AS) when both the welding direction and tool rotation direction are anticlockwise. However, when the welding direction is anticlockwise while the tool rotates clockwise, the proportions of fine Si particles decrease compared to the former situation. Furthermore, the tunnel defect is more likely to be present in the AS in the former situation.

Olivier Métais - One of the best experts on this subject based on the ideXlab platform.

  • Large eddy simulations in curved square ducts: Variation of the Curvature Radius
    Journal of Turbulence, 2007
    Co-Authors: Cécile Münch, Olivier Métais
    Abstract:

    We present large-eddy simulations of the turbulent compressible flow at a low Mach number in curved ducts. The aim is to investigate the influence of the Curvature Radius R c on the flow. Three simulations are carried out at R c = 3.5 D h , 6.5 D h and 10.5 D h (D h hydraulic diameter). We first validate our computations by comparison with the incompressible experiments performed by Chang et al. (1983, Turbulent flow in a strongly curved U-bend and downstream tangent of square cross-sections. Physico-chemical Hydrodynamics, 4(3), 243–269). We observe that the decrease of the Curvature Radius is accompanied by a strong intensification of the secondary transverse flows : a rise of 100% of the maximum of their intensity is obtained between the smaller and the higher values of R c . We show that the secondary flows strength is directly related to the radial pressure gradient intensity. We observe a significant modification of the near-wall laws in the vicinity of each curved walls in correlation with the favourable or the adverse streamwise pressure gradient depending on the nature of the Curvature. The influence of R c on the coherent vortices is also estimated.

  • Large eddy simulations in curved square ducts: variation of the Curvature Radius
    Journal of Turbulence, 2007
    Co-Authors: Cécile Münch, Olivier Métais
    Abstract:

    We present large-eddy simulations of the turbulent compressible flow at a low Mach number in curved ducts. The aim is to investigate the influence of the Curvature Radius R c on the flow. Three simulations are carried out at R c = 3.5 D h , 6.5 D h and 10.5 D h (D h hydraulic diameter). We first validate our computations by comparison with the incompressible experiments performed by Chang et al. (1983, Turbulent flow in a strongly curved U-bend and downstream tangent of square cross-sections. Physico-chemical Hydrodynamics, 4(3), 243–269). We observe that the decrease of the Curvature Radius is accompanied by a strong intensification of the secondary transverse flows : a rise of 100% of the maximum of their intensity is obtained between the smaller and the higher values of R c . We show that the secondary flows strength is directly related to the radial pressure gradient intensity. We observe a significant modification of the near-wall laws in the vicinity of each curved walls in correlation with the favo...

  • Large Eddy Simulations of the turbulent flow in curved ducts: influence of the Curvature Radius
    Direct and Large-Eddy Simulation VI, 1
    Co-Authors: Cécile Münch, Olivier Métais
    Abstract:

    We present Large-Eddy Simulations (LES) of the turbulent compressible flow in curved ducts of square cross section. The aim is to investigate the influence of the Curvature Radius Rc on the flow and the heat transfer. We consider three different Curvature radii : 4Dh, 7Dh and 11Dh (Dh hydraulic diameter). We observe a rise in the number of streamwise vortices of Gortler type on the unstable concave wall when the Curvature Radius decreases. The main effect is a strong intensification of the secondary flows with the reduction of Rc: a rise of 100 % of the intensity between the smaller and the higher case of the Curvature Radius. We determine the influence of Rc on heat transfer by considering the case of convex wall heating. Due to the modification of the secondary flows, we observe an enhancement of the heat flux for the smaller value of the Curvature Radius, specially close to the sidewalls.

Helfried K. Biernat - One of the best experts on this subject based on the ideXlab platform.

  • Magnetohydrodynamic instability of a high magnetic shear layer with a finite Curvature Radius
    Physics of Plasmas, 2002
    Co-Authors: I. L. Arshukova, Nikolai V. Erkaev, Helfried K. Biernat
    Abstract:

    This article deals with the magnetohydrodynamic instability of a thin layer which is characterized by a high magnetic shear, a constant Curvature Radius, and a plasma velocity shear. The magnetic field and the plasma parameters are considered to be piecewise constant inside the layer and in the regions adjacent to the layer. The plasma parameters and the magnetic field are assumed to obey the ideal incompressible magnetohydrodynamics. Fourier analysis is used to calculate small perturbations of the magnetic field and plasma parameters near the layer in linear approximation. The instability growth rate is obtained as a function of different parameters: the magnetic shear angle, the velocity direction angle, the tangential plasma velocity, the layer thickness, the wave number, and the Curvature Radius. The resulting instability is a mixture of interchange and Kelvin–Helmholtz instabilities on a surface with nonzero Curvature. For a fixed velocity shear and Curvature Radius, the instability growth has a maxi...

Qian Yang - One of the best experts on this subject based on the ideXlab platform.

  • Effect of weld Curvature Radius and tool rotation direction on joint microstructure in friction stir welding casting alloys
    Materials & Design, 2014
    Co-Authors: Qian Yang, Zhihan Zhang, Dalu Gao
    Abstract:

    Abstract Curved welds were designed and the effects of the weld Curvature Radius and tool rotation direction on the microstructure of friction stir welded cast aluminum alloy joints were investigated. Results show that both the weld Curvature Radius and tool rotation direction have a significant influence on the microstructure of the curved joints during FSW. With decreasing weld Curvature Radius, the size of the tunnel defect is reduces and the proportion of fine Si particles in the stir zone increases. Si particles are finer and denser in the retreating side (RS) than that in the advancing side (AS) when both the welding direction and tool rotation direction are anticlockwise. However, when the welding direction is anticlockwise while the tool rotates clockwise, the proportions of fine Si particles decrease compared to the former situation. Furthermore, the tunnel defect is more likely to be present in the AS in the former situation.