A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems

Dengfeng Liu,Dongyuan Shi,Yinhong Li 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.

Investigations on the effect of guide vane thickness and solidity on shock and unsteady flow characteristic of VNT

Dengfeng Yang,Li’ang Cao,Ce Yang,Dazhong Lao,Harold Sun 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.6

In this work, the influence of thickness and solidity of guide vane on the unsteady flow of a radial inflow turbine with variable nozzle has been numerically studied. Three vanes with the thickness changes from 0.3 to 0.1 and the solidity changes from 1.43 to 2.86, were chosen for this study. By investigating the unsteady flow field, it is found that the vane with low thickness and high solidity (vane B) can reduce shock by 75 % compared to the vane with high thickness and low solidity (base model); meanwhile, it can also mitigate the nozzle endwall leakage flow thus improves the flow uniformity of rotor inlet. As the intensity of shock and nozzle leakage flow were mitigated, the aerodynamic loading fluctuation of rotor blade can be weakened effectively, which will lead to improved rotor blades forced response. However, at small opening, vane B shows about 0.5 % lower efficiency than the base model; at large open condition, the efficiency degradation of vane B is up to 1.4 %. Therefore, there is a trade-off between the efficiency and forced response when choosing the nozzle vane solidity and thickness.

Experimental and numerical investigation on a novel gas turbocharging system for diesel engine power recovery at high altitude

Dengfeng Yang,Li’ang Cao,Yang Liu,Zhilian Zhang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

Based on the analysis of the plateau performance for a 6 cylinder 8.6 L turbocharged diesel engine, a novel gas turbocharging system (GTS) is proposed to recover the engine power at high altitudes. Besides, a rolling-reflux combustor is designed to meet the structural requirements of GTS as well as to reduce the flow loss. Both the structure of the rolling-reflux combustor and the cycle thermal calculation of the GTS were described in detail in present work. The performance changes and the fuel consumption rate with engine speed at different altitudes of the GTS are compared to the original engine. Results show that when the altitude changes from 3 km to 5 km, the torque and power of the diesel engine with GTS can be recovered to that at sea level. Then, the particle image velocimetry (PIV) test is performed to study the cold flow field at the cylinder head of the rolling-reflux combustor, and the flow conditions are analyzed in detail. Finally, the flow bench is built and the aerodynamic experiment is carried out to verify the effectiveness of GTS.

A negative stiffness vibration isolator using magnetic spring combined in combination with the rubber membrane

Qiang Li,Yu Zhu,Dengfeng Xu,Jinchun Hu,Wei Min,Lacheng Pang 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.3

The most important characteristic of a passive vibration isolator is its natural frequency and load capacity. The vibration isolation performance of a passive vibration isolator in low input frequencies is considerably improved by reducing its natural frequency. This paper presents a negative stiffness magnetic suspension vibration isolator (NSMSVI) using a magnetic spring combined with a rubber membrane to obtain lower natural frequency. To study the vibration isolation performance of the NSMSVI, the stretching force of the rubber membrane is measured through experiments. The stiffness of the rubber membrane comes from the derivative of the stretching force. A parametric study of load capacity, axial magnetic stiffness, and natural frequency of the magnetic spring is also performed. Consequently, as a case study, the size dimensions of the magnetic spring are determined. An NSMSVI table is set up for experimental validation, after which the transmissibility curves of the NSMSVI are calculated and tested. Experimental results show that the lowest natural frequency of the NSMSVI reaches 1.5 Hz with a maximum attenuation of -40 dB between 0 Hz and 100 Hz, whereas the NSMSVI has the maximum load capacity at the lowest stiffness. This paper essentially provides an efficient method to construct a negative stiffness vibration isolator for practical applications.

A New Definition of Short-circuit Ratio for Multi-converter HVDC Systems

Liu, Dengfeng,Shi, Dongyuan,Li, Yinhong The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

In this paper, a new definition of short-circuit ratio concept for multi-converter HVDC systems is proposed. Analysis results of voltage interaction between converters show that the reactive power-voltage characteristic of a converter has a dominant effect on voltage interaction level compared with its active power-voltage characteristic. Such a relation between converter reactive power and voltage interaction level supports taking the former into account in the definition of short-circuit ratio concept for multi-converter systems. The proposed definition is verified by the method of maximum power curve for various system configurations. Furthermore, a formula to calculate transient overvoltage for multi-converter systems is derived based on the proposed definition, and the efficiency of the derived formula is verified.

MicroRNA-301b promotes cell proliferation and apoptosis resistance in triple-negative breast cancer by targeting CYLD

( Hongming Song ),( Dengfeng Li ),( Tianqi Wu ),( Dan Xie ),( Kaiyao Hua ),( Jiashu Hu ),( Xiaochong Deng ),( Changle Ji ),( Yijun Deng ),( Lin Fang ) 생화학분자생물학회(구 한국생화학분자생물학회) 2018 BMB Reports Vol.51 No.11

Aberrant expression of microRNAs (miRNAs) plays important roles in carcinogenesis and tumor progression. However, the expression and biological role of miR-301b in triple-negative breast cancer (TNBC) remains unclear. Here we aimed to evaluate the roles and mechanisms of miR-301b in TNBC cells. miR-301b expression was assessed in TNBC specimens and cell lines by quantitative Real-Time PCR (qRT-PCR). TNBC cells were transfected with miR-301b mimics, inhibitors or Cylindromatosis (CYLD) small interfering RNA (siRNA) using Lipofectamine 2000. The functional roles of miR-301b were determined by cell proliferation, colony formation, and apoptosis assays. Western blots and qRT-PCR were used to measure the expression of mRNAs and proteins in the cells. We found that miR-301b was upregulated in TNBC specimens and cell lines. Overexpression of miR-301b promoted cell proliferation in TNBC cells, while inhibited the apoptosis induced by 5-FU. CYLD was downregulated by miR-301b at both mRNA and protein levels in TNBC cells. Dual-luciferase report assay confirmed that miR-301b downregulated CYLD by direct interaction with the 3’-untranslated region(3’-UTR) of CYLD mRNA. NF-κB activation was mechanistically associated with miR-301b-mediated downregulation of CYLD. However, inhibition of miR-301b reversed all the effects of miR-301b. In conclusion, miR-301b plays an oncogenic role in TNBC possibly by downregulating CYLD and subsequently activating NF-κB p65, and this may provide a novel therapeutic approach for TNBC. [BMB Reports 2018; 51(11): 602-607]

Seismic Performance Experiment Involving One-Story, Two-Bay Self-control Energy Dissipation UPPC Frames under Low Cyclic Loads

Cheng Qian,Yanhe Li,Dengfeng Xie,Ning Li,Xiaoying Wen 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.7

This paper presents an experimental study of the behavior of three one-story, two-bay unbonded partially prestressed concrete (UPPC) frames, of which two frames are self-control energy dissipation UPPC frames. This study aims to use the self-control energy dissipation UPPC frame as a new frame, and its seismic performance is evaluated compared to that of existing UPPC frames. The new frame utilizes energy dissipation components to provide energy dissipation capabilities, which allow the frame to form a beamhinge mechanism under earthquake actions. The influence of the prestress release percentage on the seismic performance of the UPPC frame is experimentally examined. The test results show that the new UPPC frame displays better ductility and energy dissipation capabilities as the prestress release percentage increases, but the lateral resistance is slightly weaker than that of a common UPPC frame. Overall, the new frame displays better seismic performance than the conventional UPPC frame and can be reused after retrofitting.

Abnormal Vacuolization of the Tapetum During the Tetrad Stage is Associated with Male Sterility in the Recessive Genic Male Sterile Brassica napus L. Line 9012A

Lili Wan,Xiuyun Xia,Dengfeng Hong,Ji Li,Guangsheng Yang 한국식물학회 2010 Journal of Plant Biology Vol.53 No.2

In the recessive genic male sterile line 9012A of Brassica napus, pollen development is affected during the tetrad stage. According to the light and electron microscopy analysis of tapetal cells and tetrads, the sterile tapetal cells swelled with expanded vacuoles at the early tetrad stage and finally filled the center of the locules where a majority of tetrads encased with the thick callose wall collapsed and degraded. We suggested that an absence of callase, which is a wall-degrading enzyme stored in the vacuoles of tapetal cells before secretion, resulted in the failure of tetrad separation. Moreover, transmission electron microscopy analysis showed that the secretory tapetal cells were not observed in sterile anthers, which indicated that the transition of the tapetum from the parietal type to the secretory type was probably aberrant. In plants, degeneration of the tapetum is thought to be the result of programmed cell death (PCD). PCD of tapetal cells was investigated by terminal deoxynucleotidyl transferasemediated dUTP nick-end labeling assay and signals indicative of deoxyribonucleic acid fragmentation were detected much earlier in sterile anther than in fertile anther. This suggests that tapetal breakdown does not occur by the normal procession of PCD and might be following an alternative mechanism of unscheduled apoptosis in line 9012A. This research supports the hypothesis that premature PCD is associated with male sterility in B. napus.

Novel Strategy for Reducing Residual Stress in Titanium Alloy Parts Obtained via Additive Manufacturing

Xinfa Sun,Yucheng Zhao,Weiming Yang,Wenyu Li,Dengfeng Yang,Haishun Liu 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12

The additive manufacturing of titanium alloy parts has important scientific significance and practical value. Controllingthe distribution of residual stress caused by the high cooling rate and temperature gradient is the key to regulating the performanceof devices obtained from additive manufacturing. In this work, the effects of the interlayer scanning angle on theresidual stress in Ti–6Al–4V parts manufactured by selective laser melting were investigated by finite element simulations. We studied how changing the interlayer deflection angle alleviated residual stress under different energy inputs. The resultsshowed that the residual stress in the z-direction was reduced by the deflection angle of 67° and 90°, and the non-uniformdistribution of residual stress was reduced by a deflection angle of 67°. The combination of a chessboard pattern and interlayerdeflection angle greatly alleviated the generation of residual stress. This work has important guiding significance forthe additive manufacturing design of high-quality and high-performance titanium alloy devices.

VGLL4 interacts with STAT3 to function as a tumor suppressor in triple-negative breast cancer

Hongming Song,Qifeng Luo,Xiaochong Deng,Changle Ji,Dengfeng Li,Amik Munankarmy,Wei Jian,Junyong Zhao,Lin Fang 생화학분자생물학회 2019 Experimental and molecular medicine Vol.51 No.-

Triple-negative breast cancer (TNBC) is an aggressive malignancy with a poor prognosis, and there are no effective molecular-targeted drugs for TNBC patients in clinical practice. The JAK-STAT pathway is implicated in tumorigenesis and the progression of various cancers. In this study, the results demonstrated that VGLL4 is expressed at low levels in both TNBC specimens and cell lines and that VGLL4 expression is negatively correlated with Ki67 expression and tumor size in TNBC patients. VGLL4 knockdown can promote the growth of TNBC cells, while VGLL4 overexpression significantly suppresses the growth of TNBC cells in vitro. More importantly, VGLL4 significantly inhibits tumor progression in a nude mouse model. In addition, VGLL4 is a direct target of miR-454, and the upregulation of miR-454 decreases VGLL4 expression and promotes the cell growth of TNBC cells. Furthermore, we also demonstrated that VGLL4 interacts with STAT3, the core component of the JAK-STAT pathway, leading to the inactivation of STAT3 and the inhibition of STAT3 downstream transcription. Collectively, these findings indicate that VGLL4 expression is negatively associated with poor prognosis in TNBC patients. High expression of miR-454 may be one of the causes of the downregulation of VGLL4 in TNBC, and VGLL4 acts as a tumor suppressor in TNBC by interacting with STAT3 and subsequently suppresses the STAT3 signaling axis, providing potential biomarkers and therapeutic approaches for this fatal disease.