Li Chen

Publications

1 Generating High-Accuracy Tool Path for 5-axis Flank Milling of Globoidal Spatial Cam

Authors: Li Chen, ZhouLong Li, Qing-zhen Bi, LiMin Zhu

Abstract:

A new tool path planning method for 5-axis flank milling of a globoidal indexing cam is developed in this paper. The globoidal indexing cam is a practical transmission mechanism due to its high transmission speed, accuracy and dynamic performance. Machining the cam profile is a complex and precise task. The profile surface of the globoidal cam is generated by the conjugate contact motion of the roller. The generated complex profile surface is usually machined by 5-axis point-milling method. The point-milling method is time-consuming compared with flank milling. The tool path for 5-axis flank milling of globoidal cam is developed to improve the cutting efficiency. The flank milling tool path is globally optimized according to the minimum zone criterion, and high accuracy is guaranteed. The computational example and cutting simulation finally validate the developed method.

Keywords: Globoidal cam, flank milling, LSQR, MINIMAX

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Abstracts

4 Prediction of Trailing-Edge Noise under Adverse-Pressure Gradient Effect

Authors: Li Chen

Abstract:

For an aerofoil or hydrofoil in high Reynolds number flows, broadband noise is generated efficiently as the result of the turbulence convecting over the trailing edge. This noise can be related to the surface pressure fluctuations, which can be predicted by either CFD or empirical models. However, in reality, the aerofoil or hydrofoil often operates at an angle of attack. Under this situation, the flow is subjected to an Adverse-Pressure-Gradient (APG), and as a result, a flow separation may occur. This study is to assess trailing-edge noise models for such flows. In the present work, the trailing-edge noise from a 2D airfoil at 6 degree of angle of attach is investigated. Under this condition, the flow is experiencing a strong APG, and the flow separation occurs. The flow over the airfoil with a chord of 300 mm, equivalent to a Reynold Number 4x10⁵, is simulated using RANS with the SST k-ɛ turbulent model. The predicted surface pressure fluctuations are compared with the published experimental data and empirical models, and show a good agreement with the experimental data. The effect of the APG on the trailing edge noise is discussed, and the associated trailing edge noise is calculated.

Keywords: Computational Fluid Dynamics, Aero-Acoustics, adverse-pressure gradient, trailing-edge noise

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3 Prediction of Bubbly Plume Characteristics Using the Self-Similarity Model

Authors: Li Chen, Alex Skvortsov, Chris Norwood

Abstract:

Gas releasing into water can be found in for many industrial situations. This process results in the formation of bubbles and acoustic emission which depends upon the bubble characteristics. If the bubble creation rates (bubble volume flow rate) are of interest, an inverse method has to be used based on the measurement of acoustic emission. However, there will be sound attenuation through the bubbly plume which will influence the measurement and should be taken into consideration in the model. The sound transmission through the bubbly plume depends on the characteristics of the bubbly plume, such as the shape and the bubble distributions. In this study, the bubbly plume shape is modelled using a self-similarity model, which has been normally applied for a single phase buoyant plume. The prediction is compared with the experimental data. It has been found the model can be applied to a buoyant plume of gas-liquid mixture. The influence of the gas flow rate and discharge nozzle size is studied.

Keywords: bubbly plume, buoyant plume, bubble acoustics, self-similarity model

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2 Curcumin Attenuates Angiogenesis in Liver Fibrosis and Inhibits Angiogenic Properties of Hepatic Stellate Cells

Authors: Li Chen, Feng Zhang, Yin Lu, Shizhong Zheng, Xiaojing Zhu, Desong Kong, Xiaoping Zhang

Abstract:

Sinusoidal pathological angiogenesis is a novel therapeutic target for liver fibrosis. We demonstrated that curcumin ameliorated fibrotic injury and sinusoidal angiogenesis in rat liver with fibrosis caused by carbon tetrachloride. Curcumin reduced the expression of angiogenic markers in fibrotic liver. Experiments in vitro showed that the viability and vascularization of rat liver sinusoidal endothelial cells (LSECs) were not impaired by curcumin. Further investigations showed that curcumin inhibited VEGF expression in hepatic stellate cells (HSCs) by disrupting PDGF-βR/ERK and mTOR pathways. HSC motility and vascularization were also suppressed by curcumin via blocking PDGF-βR/FAK/RhoA cascade. Gain- or loss-of-function analyses revealed that activation of PPARγ was required for curcumin to inhibit angiogenic properties of HSCs. We concluded that curcumin attenuated sinusoidal angiogenesis in liver fibrosis possibly by targeting HSCs via a PPARγ activation-dependent mechanism. PPARγ could be a target molecule for reducing pathological angiogenesis during liver fibrosis.

Keywords: Curcumin, angiogenesis, hepatic stellate cell, peroxisome proliferator-activated receptor-γ

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1 Platelet-Derived Growth Factor-Β Receptor/P38 Pathway May Be the Potential Liver Damage Mechanisms Caused by Saikosaponin D

Authors: Li Chen, Feng Zhang, Shizhong Zheng

Abstract:

SaikosaponinD (SSD) is a major component of saikosaponins isolated from Bupleurumfalactum. Our current study was to examine the toxic effect of SSD on liver cells and explore the possible mechanism. The results demonstrated that SSD induced mouse liver injury and led to apoptosis in LO2 cells. HE staining and TUNEL analyses showed that SSD stimulated liver injury and hepatocyte apoptosis in vivo. Subsequent experiments showed that SSD down-regulated Bcl-2 but up-regulated Bax. In vitro, SSD-treated LO2 cells exhibited apparent down-regulated expression of p-p38. Moreover, PDGF-βR agonist PDGF-BB alone significantly upregulated p38 phosphorylation, while combined with SSD, p38 phosphorylation expression was reduced. Furthermore, shRNA-mediated PDGF-βR knockdown augmented the inactivation of p-p38 and Bcl2 but abrogated the activation of Bax, these results were more obvious when shRNA combined with SSD. These data indicated that SSD stimulated liver injury and apoptosis in hepatocytes and PDGF-βR /p38 pathway may be the potential mechanistic.

Keywords: apoptosis, saikosaponin D, hepatotoxicity, liver injury, platelet-derived growth factor-β receptor, p38

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