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Experimental study on visualization of the flow field in microtube

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Science China(Technological Sciences) 2005年第5期48卷 521-529页

作者： liu Zhigang ZHAO Yaohua Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China

An experimental study was conducted to visualize the flow field and confirm the transitional Reynolds number from laminar to turbulent flow, as distilled water flows through quartz glass microtubes with inner diameter 315 and 520 μm. With gentian violet as colorant, the flow field pictures in the microtube, and therefore, is shot by a CCD camera with a microscope at different Reynolds numbers. Pressure drop data were also used to characterize the friction factor for those microtubes in the Reynolds number range of 200–2300. The experimental results clearly showed that the flow in the microtube was the laminar state and the friction factors agreed well with the Poiseuille equations when the Reynolds number was low. As the Reynolds number was larger than 1200 and 1500 for the microtube with inner diameter 315 and 520 μm, respectively, the friction factor departed from the classical laminar solution due to the earlier transition from laminar to tubulent flow. The flow turned into full turbulent when the Reynolds number reached 1500–1800.

关键词： visual experiment, microtube, microscale flow, friction factor, turbulent transition.

EXACT SOLUTIONS FOR FREE IN-PLANE VIBRATIONS OF RECTANGULAR PLATES

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Acta Mechanica Solida Sinica 2011年第6期24卷 556-567页

作者： Bo liu Yufeng Xing The Solid Mechanics Research Center Beijing University of Aeronautics and Astronautics Beijing 100191 China

All possible exact solutions are successfully obtained in terms of 10 sets of distinct eigensolutions for the free in-plane vibration of isotropic rectangular plates. The plates have simply supported condition at two opposite edges and any combination of classical boundary conditions at the other two edges. The exact solutions are validated through both mathematical proof and comparisons with the solutions of differential quadrature method. Some unusual phenomena are revealed in free in-plane vibrations of rectangular plates due to one of the eigenvalues being zero. This work constitutes an improved version of very recent corresponding work by the same authors lint. J. Mech. Sci., 2009, 51： 246-255]. Both the solution forms and solving procedures in the previous work are substantially simplified. Some new results are also given, which are useful for validation purpose in future.

关键词： rectangular plate in-pane free vibration frequency mode shape exact solution

New results on global output-feedback stabilization for nonlinear systems with unknown growth rate

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控制理论与应用（英文版） 2013年第3期11卷 401-408页

作者： Xuehua YAN Yungang liu School of Control Science and Engineering Shandong University

In this paper, the global asymptotic stabilization by output feedback is investigated for a class of uncertain nonlinear systems with unmeasured states dependent growth. Compared with the closely related works, the remarkableness of the paper is that either the growth rate is an unknown constant or the dimension of the closed-loop system is significantly reduced, mainly due to the introduction of a distinct dynamic high-gain observer based on a new updating law. Motivated by the related stabilization results, and by skillfully using the methods of universal control and backstepping, we obtain the design scheme to an adaptive output-feedback stabilizing controller to guarantee the global asymptotic stability of the resulting closed-loop system. Additionally, a numerical example is considered to demonstrate the effectiveness of the proposed method.

关键词： Uncertain nonlinear systems Global asymptotic stabilization Adaptive control Output feedback Dynamic high gain

Comparative Mountain Hydrology: A Case Study of Wis?ok River in Poland and Chaohe River in China

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Chinese Geographical Science 2015年第1期25卷 1-12页

作者： Leszek SOBKOWIAK liu Changming Department of Hydrology and Water Management Institute of Physical Geography and Environmental Planning Adam Mickiewicz University Institute of Geographic Sciences and Natural Resources Research Chinese Academy of Sciences

Hydrological processes in river basins of similar size and morphology may differ significantly due to different climatic conditions. This paper presents a comparative analysis of hydrological characteristics of two river basins located in different climatic zones: the Wisok River Basin in the south-eastern Poland and the Chaohe River Basin in the northern China. The criteria of their choice were similarities in the basin area, main river length and topography. The results show that climate plays a key role in shaping fluvial conditions within the two basins. It is concluded that: 1) precipitation in the Wisok River Basin is more evenly distributed in the yearly cycle, while in the Chaohe River Basin it is highly concentrated in the few summer months; 2) spring snowmelt significantly contributes to runoff in the Wisok River Basin, while its role in the Chaohe River Basin is negligible; 3) in the Wisok River Basin, besides the peak flow in spring, there is also a period of high water in summer resulting from precipitation, while in the Chaohe River Basin there is only one high water period in summer; 4) the Wisok River Basin shows relatively higher stability in terms of the magnitude of intra- and inter-seasonal discharges; 5) during the multi-year observation period, a decrease in both precipitation and runoff was recorded in the two river basins.

关键词： comparative hydrology mountain area Wislok River Basin Chaohe River Basin seasonal changes inter-annual changes

Nao-Fu-Cong ameliorates diabetic cognitive dysfunction by inhibition of JNK/CHOP/Bcl2-mediated apoptosis in vivo and in vitro

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Chinese Journal of Natural Medicines 2020年第9期18卷 704-713页

作者： JING Guang-Chan liu Di liu Yu-Qin ZHANG Meng Ren Deparment of Traditional Chinese Medicine Peking Union Medical Collge HospitalPeking Union Medical Collge and Chinese Academy of Medical SciencesBeijing 100730China Deparment 0f cell resource center Institute of Basic Medical SciencePeking Union Medical College and Chinese Academy of Medical SciencesBeijing 100730China

Chinese herbal compound Nao-Fu-Cong(NFC) has been mainly used to treat cognitive disorders in Traditional Chinese Medicine(TCM). The present study aimed to investigate whether its neuroprotective effects might be related to the inhibition of JNK/CHOP/Bcl2-mediated apoptosis pathway or not. We randomly assigned STZ(60 mg·k^(-1))-induced diabetic rats into control group, diabetic model group and NFC groups(low-dose, medium-dose and high-dose). The primary culture of hippocampal neurons were transferred into different culture media on the third day. The cells were then divided into control group, high-glucose group, NFC(low-dose, medium-dose and high-dose) groups, CHOP si-RNA intervention group, JNK pathway inhibitor SP600125 group and oxidative stress inhibitor N-acetylcysteine(NAC) group. NFC significantly improved the cognitive function of diabetic rats, and had neuroprotective effect on hippocampal neurons cultured in high glucose. Further research results showed that NFC could reduce the apoptosis of hippocampal neurons in rats with diabetic cognitive dysfunction. NFC had inhibitory effects on CHOP/JNK apoptosis pathway induced by high glucose, and also decreased the levels of ROS and increased the mitochondrial membrane potential. These suggested that the neuroprotective effect of NFC might be related to the inhibition of CHOP and JNK apoptotic signaling pathways, and the cross pathway between oxidative stress and mitochondrial damage pathway.

关键词： Nao-Fu-Cong Apoptosis High glucose Hippocampal neurons

Research on dynamic characteristics of multi-sensor system in the case of cross-sensitivity

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Science China(Technological Sciences) 2005年第1期48卷 1-22页

作者： TANG Xiaojun liu Junhua School of Electrical Engineering Xi'an Jiaotong University Xi'an 710049 China School of Electrical Engineering Xi'an Jiaotong University Xi'an 710049 China

In this study, the dynamic characteristic of a multi-sensor system made up of such sensors as are sensitive to several parameters is discussed, and the effect of cross-sensitivity on the precision of a measurement system is also discussed. A multi-sensor system is looked as a serial of a linear filter and a memoryless nonlinear system, i.e. Wiener system, and the subsequent information fusion system is regarded as a Hammerstein system, i.e. a serial of a memoryless nonlinear system and a linear filter. On the basis of static calibration, it is presented to determine the inverse filter in a Hammerstein system using blind deconvolution. In order to control the uncertainty of amplitude of signals recovered by blind deconvolution well, a regulation approach to regulating the inverse linear filter coefficient matrixes is presented according to the identity between inverse filter coefficient matrixes and static calibrating matrix. So the approximate inverse dynamic model of multi-sensor system is obtained, the degree of distortion of dynamic measurement result is reduced, the measurement precision is improved, and the need of practice can be reached. Simulation example and simulation result show that the recovered error of the inputs of sensor system, the frequency of which is 1/10 of sampling frequency, is 1/20 of the measurement results without dynamic compensation, and is one half of the measurement results with sole dynamic compensation, and the rapidity is improved 2 times. The dynamic compensation results of a metal oxide semiconductor methane sensor show that the dynamic measurement error is less than one half of that without dynamic compensation. So this method expands the bandwidth of multi-sensor system.

关键词： dynamic compensation, multi-sensor system, cross-sensitivity, blind deconvolution.

3D printing of high-performance micro-supercapacitors with patterned exfoliated graphene/carbon nanotube/silver nanowire electrodes

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Science China(Technological Sciences) 2021年第5期64卷 1065-1073页

作者： liu Lang LU JunYong LONG XinLin ZHOU Ren liu YingQuan WU YiTing YAN KangWei National Key Laboratory of Science and Technology on Vessel Integrated Power System Naval University of EngineeringWuhan 430033China

Micro-supercapacitors(MSCs)show great potential as on-chip energy storage devices for portable *** major flaw of thin-film MSCs is their low energy *** improve the energy density,thicker electrodes are ***,the fabrication of MSCs with thick electrodes remains a *** this work,a novel 3D printing method is employed to fabricate high-performance MSCs with interdigitated exfoliated graphene(EG)/carbon nanotube(CNT)/silver nanowire(Ag NW)*** nanowelding of Ag NW junction plays a critical role in the realization of 3D *** enhance the electrochemical performances of EG,phosphorus atoms are incorporated into the carbon framework with 1.7 at%.The areal capacitance of the 3D printed MSC is 21.6 mF cm^(-2)at a scan rate of 0.01 V s^(-1).The areal energy density of the MSC ranges from 0.5 to 2μWh cm^(-2)with a maximum power density of 2.5 mW cm^(-2).

关键词： micro-supercapacitor 3D printing silver nanowire exfoliated graphene micro-plasma-jet

Flame-retardant and antibacterial flexible polyurethane foams with high resilience based on a P/N/Si-containing system

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Journal of Materials Science & Technology 2024年第15期182卷 141-151页

作者： Ping Li Hui liu Ying-Jun Xu De-Yi Wang Yun liu Ping Zhu College of Textiles&Clothing Institute of Functional Textiles and Advanced MaterialsNational Engineering Research Center for Advanced Fire-Safety Materials D&A(Shandong)Qingdao Key Laboratory of Flame Retardant Textile MaterialsState Key Laboratory of Bio-Fibers and Eco-TextilesQingdao UniversityQingdao 266071China IMDEA Materials Institute C/Eric Kandel 2GetafeMadrid 28906Spain

In this work,the coatings used phosphorylated chitosan(PCS)and GP-108 via the dip-coating method presented exceptional flame retardancy and antibacterial properties for flexible polyurethane foams(FPUF).PCS/GP@FPUF with 35%weight gain of PCS/GP can receive the UL-94 V-0 rating and obtain a 32%reduction of peak heat release rate value compared with that of FPUF,and it remains relatively dense char *** effective heat of combustion of PCS/GP@FPUF is 21.6 kJ/g,presenting a 22%decrease compared with that of ***,the PCS/GP coatings mainly have the condensed-phase flame-retardant mechanism associated with the analysis of char residues and the volatile products released through the thermal degradation process.X-ray photoelectron spectroscopy results confirm that the char residues of PCS/GP@FPUF consist of highly-graphitized carbon and it formed P-N-Si synergistic char *** addition,the antibacterial rates of PCS/GP@FPUF against Escherichia coli(***)and Staphylococcus aureus(***)are 99.99%,and the incorporation of GP-108 does not influence the antibacterial proper-ties of ***,the resiliency of FPUFs has been slightly ***,the flame-retardant and antibacterial FPUFs with wonderful resiliency are hopeful to be applied as filler materials for vehicle seats and obtain longer service lives.

关键词： Environmental organic-inorganic coatings FPUF Flame retardancy Antibacterial properties

Pseudo core-shell LaCoO3@MgO perovskite oxides for high performance methane catalytic oxidation

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Journal of Rare Earths 2021年第1期39卷 51-57,I0002页

作者： Saifei Wang Jie liu Yiyuan Zhang Peiqi Chu Haobin liu Man Wang Erhong Duan School of Environmental Science and Engineering Hebei University of Science and TechnologyShijiazhuang 050018China

Magnesia modified LaCoO3 was prepared by a facile one-step sol-gel method and used for removal of dilute *** with the conventional doping technique,the obtained LaCoO3@MgO-x exhibits pseudo core-shell structure and shows superior catalytic *** methane conversion exceeds90%at 532℃on LaCoO3@MgO-0.1,while only 60%of methane is conversed using the doped perovskite *** high catalytic performance of LaCoO3@MgO-0.1 is mainly attributed to the adjustment of surface acid-base properties by the MgO shell *** to density functional theory(DFT)calculation,the methane is more likely to be adsorbed and cracked on LaCoO3@*** in situ DRIFTS shows that CH3-O-CH3 intermediate specie is *** pseudo core-shell structure also enhances the stability and the LaCoO3@MgO-0.1 maintains high activity after working for 100 *** above results demonstrate that surface modification by magnesia is an effective strategy for improving LaCoO3 catalytic performance.

关键词： Perovskite oxides Core-shell structure Surface acid-base properties Methane catalytic oxidation Rare earths