Search results for: Jianqiang Lin

Authors: Mesfin Angaw Tesfay, Xin Win, Jianqiang Lin, Jianqun Lin

Abstract:

L-Xylose is a crucial intermediate in pharmaceuticals, used in the production of various antiviral and anticancer medications. However, it is a rare and expensive sugar with limited natural availability. Recently, enzymatic methods for producing L-xylose have gained significant interest due to their advantages over traditional chemical synthesis. In this study, a novel approach was developed to produce L-xylose from the inexpensive starting material, xylitol. The L-fucose isomerase (L-fucI) gene from Escherichia coli K-12 and the Xylitol-4-dehydrogenase (xdh) gene from Pantoea ananatis ATCC 43072 were cloned and co-expressed in Escherichia coli, resulting in recombinant cells containing the vector PET28a-xdh/L-fucI. The co-expression system achieved optimal activity at 40°C and pH 10.0, with the addition of 7.5 mM Zn²⁺ increasing the catalytic activity by 1.34-fold. This system produced 52.2 g/L of L-xylose from an initial xylitol concentration of 80 g/L, corresponding to a conversion rate of 65% and productivity of 1.86. This study provides a viable approach for producing L-xylose from xylitol using a co-expression system harboring L-fucI and xdh genes.

Keywords: L-fucose isomerase, xylitol-4-dehydrogenase, L-xylose, xylitol, co-expression

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Authors: Guohua Tu, Zhi Fu, Zhiwei Hu, Neil D Sandham, Jianqiang Chen

Abstract:

Tripping of boundary-layers from laminar to turbulent flow, which may be necessary in specific practical applications, requires high amplitude disturbances to be introduced into the boundary layers without large drag penalties. As a possible improvement on fixed trip devices, a technique based on vortex shedding for enhancing supersonic flow transition is demonstrated in the present paper for a Mach 1.5 boundary layer. The compressible Navier-Stokes equations are solved directly using a high-order (fifth-order in space and third-order in time) finite difference method for small-scale cylinders suspended transversely near the wall. For cylinders with proper diameter and mount location, asymmetry vortices shed within the boundary layer are capable of tripping laminar-turbulent transition. Full three-dimensional simulations showed that transition was enhanced. A parametric study of the size and mounting location of the cylinder is carried out to identify the most effective setup. It is also found that the vortex shedding can be suppressed by some factors such as wall effect.

Keywords: boundary layer instability, boundary layer transition, vortex shedding, supersonic flows, flow control

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