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Search Results: 1 - 10 of 28240 matches for " Youfeng Zhu "
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Modeling and Dynamical Behavior of Rotating Composite Shafts with SMA Wires
Yongsheng Ren,Qiyi Dai,Ruijun An,Youfeng Zhu
Shock and Vibration , 2014, DOI: 10.1155/2014/765875
Abstract: A dynamical model is developed for the rotating composite shaft with shape-memory alloy (SMA) wires embedded in. The rotating shaft is represented as a thin-walled composite of circular cross-section with SMA wires embedded parallel to shaft’s longitudinal axis. A thermomechanical constitutive equation of SMA proposed by Brinson is employed and the recovery stress of the constrained SMA wires is derived. The equations of motion are derived based on the variational-asymptotical method (VAM) and Hamilton’s principle. The partial differential equations of motion are reduced to the ordinary differential equations of motion by using the Galerkin method. The model incorporates the transverse shear, rotary inertia, and anisotropy of composite material. Numerical results of natural frequencies and critical speeds are obtained. It is shown that the natural frequencies of the nonrotating shaft and the critical rotating speed increase as SMA wire fraction and initial strain increase and the increase in natural frequencies becomes more significant as SMA wire fraction increases. The initial strain of SMA wires appears to have marginal effect on dynamical behaviors of the shaft. The actuation performance of SMA wires is found to be closely related to the ply-angle. 1. Introduction Composite materials have found the increased applications for replacement of the conventional metallic materials in the rotating flexible shaft employed for drive shafts of helicopters, steam, and gas turbines. This is likely attributed to high stiffness and strength/weight ratios of composite shaft compared with its metallic counterparts. The development trend in design of light-weight composite shafts is towards higher operating speeds, which gives rise to the problems of high vibration amplitude and stability. Seeking the solution of these problems has caused great research effort [1] in the dynamic of composite rotor. A review on the literature in this area has shown that composite shafts have high whirling resistance capability and are less susceptible to dynamic instability associated with metallic shafts [2]. Several attempts to develop mathematical models of spinning composite shafts are reported in the literature. These models include the shaft models based on shell theories [3], or beam theories combined with the strain—displacement relations of the shell theories [4], or a thin-walled beam theory [5]. Song et al. [5] developed the composite thin-walled shaft model based on a thin-walled beam theory of Rehfield [6]. This model was used to investigate the natural frequencies and
THE NONLINEAR INTERACTION BETWEEN DIFFERENT WAVE COMPONENTS AND THE PROCESS OF INDEX CYCLE OF GENERAL CIRCULATION

Xu Youfeng,

大气科学进展 , 1986,
Abstract: By using a two-level quasi-geostrophic truncated spectral model taking account of the nonlinear in-teraction between different wave components (i. e. basic current, ultra-long waves and long waves), the index cycle of general circulation is investigated. The calculated results show that the circulation index has a, quasi-periodic vacillation with a period of 8 to 16 days, which can be created by the nonlinear interaction and that the nonlinear interaction between different wave components may cause the tilted-trough vacillation, amplitude vacillation of wave pattern and quasi-periodic change of wave number of flow pattern.
AMP-Activated Protein Kinase Suppresses the In Vitro and In Vivo Proliferation of Hepatocellular Carcinoma
Jidong Cheng, Tianliang Huang, Youfeng Li, Yubai Guo, Yuzhang Zhu, Qingjia Wang, Xiaojun Tan, Weisheng Chen, Yongneng Zhang, Weijie Cheng, Tetsuya Yamamoto, Xubin Jing, Jiexiong Huang
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0093256
Abstract: AMP-activated protein kinase (AMPK) is a central metabolic sensor and plays an important role in regulating glucose, lipid and cholesterol metabolism. Therefore, AMPK is a key therapeutic target in diabetes. Recent pilot studies have suggested that diabetes drugs may reduce the risk of cancer by affecting the AMPK pathway. However, the association between AMPK and the proliferation of hepatocellular carcinoma (HCC) is unknown. In this study, we investigated the relationship between AMPK activity and the proliferation of HCC in cell lines, nude mice and human clinic samples. We first investigated the relationship between AMPK activity and cell proliferation in two HCC cell lines, PLC/PRF/5 and HepG2, by two AMPK activators, 5-aminoimidazole-4-carboxamide-1-h-D-rib?ofuranoside(AICAR) and metformain. AICAR and metformin treatment significantly inhibited the proliferation of HCC cells and induced cell cycle arrest at G1-S checkpoint. We then observed that metformin abrogated the growth of HCC xenografts in nude mice. The clinical pathology of AMPK activity in HCC, including cell proliferation, differential grade, tumor size and microvessel density, was studied by using 30 clinical tissue samples. In HCC tissue samples, phosphorylated AMPK was expressed mainly in cytoplasm. AMPK activity decreased significantly in HCC in comparison with paracancerous liver tissues (P<0.05). AMPK activity was negatively correlated with the level of Ki-67 (a marker of cell proliferation), differential degradation and tumor size (P<0.05), but not with microvessel density, hemorrhage or necrosis in HCC. Our findings suggest that AMPK activity inhibits the proliferation of HCC and AMPK might be an effective target for prevention and treatment of HCC.
Variation of soil Δδ 13C values in Xifeng loess-paleosol sequence and its paleoenvironmental implication
Youfeng Ning,Weiguo Liu,Zhisheng An
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-1350-7
Abstract: The carbon isotopic compositions of soil organic matter (SOM) and total carbonate (TC) in Xifeng loess-paleosol sequence have been studied. The δ 13CSOM values vary from 23.8‰ to 20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ 13CSOM values, the δ 13CTC values vary from 8.5‰ to 3.6‰ and are lower in interglacial than in glacial stages. The differences (Δδ 13C) between the δ 13CSOM and δ 13CTC values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loess-paleosol sequence indicate that the Δδ 13C values represent the ratio of primary carbonate (PC) to secondary carbonate (SC). The Δδ 13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6:4. But in the paleosol stages, the Δδ 13C values were low, with a small proportion of PC. The Δδ 13C values in loess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC.
不同尺度波动的非线性相互作用和大气的指数循环过程
许有丰 Xu Youfeng
大气科学 , 1984, DOI: 10.3878/j.issn.1006-9895.1984.04.04
Abstract: 本文用两层准地转截谱模式,考虑基本气流、超长波和长波之间的非线性相互作用,得出了大气环流指数循环这种准周期振荡过程,其周期为8—15天.数值计算表明:非线性相互作用可以产生大气行星波螺旋状槽线倾斜的谐振、不同尺度波动的振幅谐振以及大型环流波数变化的准周期振荡.
大地形和定常热源对大气环流指数循环过程的影响
许有丰 Xu Youfeng
大气科学 , 1988, DOI: 10.3878/j.issn.1006-9895.1988.t1.09
Abstract:
A Modification of Minimal Residual Iterative Method to Solve Linear Systems
Xingping Sheng,Youfeng Su,Guoliang Chen
Mathematical Problems in Engineering , 2009, DOI: 10.1155/2009/794589
Abstract: We give a modification of minimal residual iteration (MR), which is 1V-DSMR to solve the linear system =. By analyzing, we find the modifiable iteration to be a projection technique; moreover, the modification of which gives a better (at least the same) reduction of the residual error than MR. In the end, a numerical example is given to demonstrate the reduction of the residual error between the 1V-DSMR and MR.
The nonlinear interaction between different wave components and the process of index cycle of general circulation
不同尺度波动的非线性相互作用和大气的指数循环过程

Xu Youfeng,
许有丰

大气科学 , 1984,
Abstract: 本文用两层准地转截谱模式,考虑基本气流、超长波和长波之间的非线性相互作用,得出了大气环流指数循环这种准周期振荡过程,其周期为8—15天.数值计算表明:非线性相互作用可以产生大气行星波螺旋状槽线倾斜的谐振、不同尺度波动的振幅谐振以及大型环流波数变化的准周期振荡.
Hardware-Software Collaborative Techniques for Runtime Profiling and Phase Transition Detection
Youfeng Wu,Yong-Fong Lee,
Youfeng Wu
,and Yong-Fong Lee

计算机科学技术学报 , 2005,
Abstract: Dynamic optimization relies on runtime profile information to improve the performance of program execution. Traditional profiling techniques incur significant overhead and are not suitable for dynamic optimization. In this paper, a new profiling technique is proposed, that incorporates the strength of both software and hardware to achieve near-zero overhead profiling. The compiler passes profiling requests as a few bits of information in branch instructions to the hardware, and the processor executes profiling operations asynchronously in available free slots or on dedicated hardware. The compiler instrumentation of this technique is implemented using an Itanium research compiler. The result shows that the accurate block profiling incurs very little overhead to the user program in terms of the program scheduling cycles. For example, the average overhead is 0.6% for the SPECint95 benchmarks. The hardware support required for the new profiling is practical. The technique is extended to collect edge profiles for continuous phase transition detection. It is believed that the hardware-software collaborative scheme will enable many profile-driven dynamic optimizations for EPIC processors such as the Itanium processors.
Variation of soil Δδ 13C values in Xifeng loess-paleosol sequence and its paleoenvironmental implication
Variation of soil Δδ13C values in Xifeng loess-paleosol sequence and its paleoenvironmental implication

Youfeng Ning,Weiguo Liu,Zhisheng An,
NING
,Youfeng,LIU,Weiguo,AN,Zhisheng

科学通报(英文版) , 2006,
Abstract: The carbon isotopic compositions of soil organic matter (SOM) and total carbonate (TC) in Xifeng loess-paleosol sequence have been studied. The δ 13CSOM values vary from 23.8‰ to 20.2‰, which are higher in interglacial than in glacial stages. Contrary to δ 13CSOM values, the δ 13CTC values vary from 8.5‰ to 3.6‰ and are lower in interglacial than in glacial stages. The differences (Δδ 13C) between the δ 13CSOM and δ 13CTC values vary from 14.1‰ to 19.4‰. Our results from the Xifeng loess-paleosol sequence indicate that the Δδ 13C values represent the ratio of primary carbonate (PC) to secondary carbonate (SC). The Δδ 13C values were high in the loess stages, and the maximal PC-to-SC ratio can reach 6:4. But in the paleosol stages, the Δδ 13C values were low, with a small proportion of PC. The Δδ 13C values in loess-paleosol sequence also indicate the contributions of the dust to the loess sediment in the Chinese Loess Plateau because the dust contains the PC.
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