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The formation and precipitation mechanism of two ordered patterns of embedded convection in stratiform cloud

Science China Earth Sciences 2012年第1期55卷 113-125页

作者： LI YanWei niu ShengJie Key Laboratory for Atmospheric Physics and Environment of China Meteorological Administration Nanjing University of Information Science&TechnologyNanjing 210044China

Although convection embedded in stratiform cloud is often disordered, it is ordered under certain weather conditions. In particular, there are two forms of ordered convection: embedded convection with a ladder-like pattern and that with a parallel pattern. However, there is little literature regarding these patterns. Because stratiform clouds with embedded convection are major objects for weather-modification studies, it is important to explore the formation/development and characteristic precipitation of embedded convection from the perspective of cloud and precipitation physics. In this paper, using observation data, we simulate a large-scale precipitation event in China for July 19-21, 2007, employing the mesoscale Weather Research and Forecasting (WRF) model (V2.2). The rainfall-related clouds are analyzed through simulation, with particular focus being given to the genesis of embedded convection, the precipitation and microphysical properties. The results show that the WRF model can simulate features of this kind of nephsystem, indicating a close relationship between convection genesis and the 500 hPa trough and low-level convergence line. In such a favorable weather situation, there are two ordered patterns of embedded con- vection in the nephsystem, one being a group of convection centers arranged at different altitudes in a ladder-like manner and the other being a group of convection centers with a parallel pattern. In the first case, rainfall also has a ladder feature, with precipitation being highest for the top convection and reducing to the base convection. This implies that the higher the convection develops, the more active the microphysics in warmand cold-cloud processes is, leading to greater precipitation; i.e. rainfall in a ladder-like distribution. In the second case, rainfall decreases step by step from south to north, with the precipitation depending strongly on the cloud-water content therein. The two patterns of embedded convection and their p

关键词： numerical modeling embedded convection ladder-like distribution parallel distribution

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An integrative mathematical model of microwave ion thruster for mHz-frequency thrust noise analysis

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Chinese Journal of Aeronautics 2024年第4期37卷 121-136页

作者： Xiang niu Hui LIU Daren YU Plasma Propulsion Laboratory Harbin Institute of TechnologyHarbin 150001China

Many high-precision space missions need thrusters to produce thrust with low noise to compensate for disturbances and ensure satellite platform stability. Microwave ion thruster is characterized with a wide thrust range and potential for these missions. A cost-effective and accurate mathematical model is crucial for mHz-frequency thrust noise analysis and feedback controller design. The Particle-In-Cell(PIC) and global models are two common simulation tools. The PIC model is characterized with high accuracy but huge computation cost, which is difficult to analyze long-time performance characteristics. Now, the global model is only used for the discharge chamber with low accuracy and cannot reflect ion extraction properties. In this paper, an integrative mathematical model is built for a 1-cm microwave ion thruster and can reflect ion beamlet divergence and impingement on the Accelerator Grid(AG). Simulation results show good agreement with experiments at 0.06 sccm. However, the model demonstrates worse consistency with experiments when the flux increases to 0.1 sccm, which may be because the influence of neutral gas on the Electron Cyclotron Resonance(ECR) is not considered in the model. A long-time(1000 s) simulation is conducted with this model under 35 μN. It takes 3 hrs, and the thrust noise reaches 1 μN/Hz^(0.5) at 1 mHz.

关键词： Electric propulsion Microwave ion thruster Integrative model Sheath property Ion beamlet divergence Thrust noise Plasma

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Event-Triggered Adaptive Fuzzy Finite Time Control of Fractional-Order Non-Strict Feedback Nonlinear Systems

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Journal of Systems Science & Complexity 2022年第6期35卷 2166-2180页

作者： XIN Chun LI Yuanxin niu Ben College of Science Liaoning University of TechnologyJinzhou 121001China School of Information Science and Engineering Shandong Normal UniversityJinan 250014China

In this article,the problem of event-triggered adaptive fuzzy finite time control of nonstrict feedback fractional order nonlinear systems is *** using the property of fuzzy basis function,the obstacle caused by algebraic loop problems is successfully ***,a new adaptive event-triggered scheme is designed under the unified framework of backstepping control method,which can largely reduce the amount of *** stability of the closed-loop system is ensured through fractional Lyapunov stability ***,the effectiveness of the proposed scheme is verified by simulation examples.

关键词： Backstepping control event-triggered control(ETC) fractional order nonlinear system(FONS) fuzzy logic system(FLS) non-strict feedback structure

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Vascularization ability of glioma stem cells in different three-dimensional microenvironments

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Regenerative Biomaterials 2024年第1期3卷 34-43页

作者： Xuanzhi Wang Tao Xu Chaoshi niu Department of Neurosurgery The First Affliated Hospital of USTCDivision of Life Sciences and MedicineUniversity of Science and Technology of ChinaHefeiAnhui230036China Department of Neurosurgery Sichuan Provincial People's HospitalUniversity of Electronic Science and Technology of ChinaChengdu 610072People's Republic of China Center for Bio-intelligent Manufacturing and Living Matter Bioprinting Research Institute of Tsinghua University in ShenzhenTsinghua UniversityShenzhen 518057People's Republicof China

Glioblastoma(GBM)is among the most common and aggressive adult central nervous system *** prominent charac-teristic of GBM is the presence of abnormal microvessels.A significant correlation between angiogenesis and prognosis has been *** reconstructing this neovascula-rization and tumor microenvironment through personalized in vitro disease models presents a significant ***,it is crucial to develop new anti-angiogenic therapies for *** this study,3D bioprinted glioma stem cell(GSC)-laden hydrogel scaffolds,hybrid Gsc hydrogels and ceil-free hydrogel scaffolds were manufactured to investigate the vas-cularization ability of GsCs in varying 3D microenvironments.

关键词： 3D bioprinting xenograft tumors GSC-laden hydrogel scaffold glioblastoma angiogenesis

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An Experimental Validation Study on Ferrofuid Evaporation

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Chinese Journal of Mechanical Engineering 2022年第4期35卷 159-168页

作者： Wenjuan Yu Decai Li Sifang niu School of Mechanical Electronic and Control Engineering Beijing Jiaotong UniversityBeijing 100044China State Key Laboratory of Tribology Tsinghua UniversityBeijing 100084China

The current research on the evaporation of ferrofuids mainly focuses on the characterization of ultra-low vapor pressure ferrofuids in vacuum and the theoretical analysis of the evaporation *** studies have focused on the experimental validation of the proposed evaporation rate equations and on the comparison of the diferences in ferrofuid *** this study,based on the Bolotov’s model,an evaporation rate equation is deduced from the experimental *** experimental study included a comparison of the evaporation,magnetic particle volume fraction,temperature,height of the fuid surface from the outlet,and magnetic feld of a kerosene-based ferrofuid and its base carrier *** prepared sample was evaporated in a test tube,and the evaporation rate was calculated by measuring the weight loss of the *** experimental results show that the evaporation rate of the base carrier liquid is higher than that of the *** smaller the volume fraction of the magnetic particles,the greater the evaporation *** magnetic particles play a key role in preventing evaporation of the base *** higher the temperature,the smaller the deviation of the evaporation rate from the predicted *** evaporation rates obtained by the two control groups at the height of the fuid surface from the outlet were lower than the predict *** magnetic feld had a certain promotional efect on the evaporation of the *** experimental results were consistent with the results obtained using Bolotov’s *** research validates Bolotov’s model and shows that the model is somewhat biased but still responds well to diferent variables.

关键词： Evaporation rate Experimental study Ferrofuid Kerosene Magnetic feld Validation

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Fast division-free parallel structure for convolution perfectly matched layer in finite difference time domain method

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The Journal of China Universities of Posts and Telecommunications 2015年第1期22卷 72-76,82页

作者： Bai Bing niu Zhongqi niu Yi Wei Bing Zhao Gang School of Electronic Engineering Xidian University School of Physics and Optoelectronic Engineering Xidian University

Parallel acceleration of convolution perfectly matched layer （CPML） algorithm suffers from massive division operation which is widely accepted as one of the most expensive operations for the equipment such as graphic processing unit （GPU）, field programmable gate array （FPGA） etc. In pursuit of higher efficiency and lower power consumption, this article revisited the CPML theory and proposed a new fast division-free parallel CPML structure. By optimally rearranging the CPML inner iteration process, all the division operators can be eliminated and replaced by recalculating the related field updating coefficients offline. Experiments show that the proposed division-free structure can save more than 50% arithmetic instructions and 25% execution time of the traditional parallel CPML structure without any accuracy loss.

关键词： division elimination convolution perfectly matched layer finit difference time domain parallel computing graphic processing unit

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Models to predict sunlight-induced photodegradation rates of contaminants in wastewater stabilisation ponds and clarifiers

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Water Science and Engineering 2019年第4期12卷 293-297页

作者： Xi-Zhi niu Department of Chemical and Environmental Engineering and Arizona Laboratory for Emerging Contaminants University of Arizona

Two kinetic models were established for conservative estimates of photodegradation rates of contaminants under sunlight irradiation,in particular for wastewater stabilisation ponds and clarifiers in conventional wastewater treatment *** two models were designated for(1)contaminants with high photolytic rates or high photolytic quantum yields,whose photodegradation is unlikely to be enhanced by aquatic photosensitisers;and(2)contaminants withstanding direct photolysis in sunlit waters but subjected to indirect *** effortlessly intelligible prediction procedure involves sampling and analysis of real water samples,simulated solar experiments in the laboratory,and transfer of the laboratory results to realise water treatment using the prediction *** similar models have been widely used for laboratory studies,this paper provides a preliminary example of translating laboratory results to the photochemical fate of contaminants in real waters.

关键词： Sunlight irradiation Photodegradation Contaminants Stabilisation ponds Solar water treatment

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A Novel Video Reversible Data Hiding Algorithm Using Motion Vector for H.264/AVC

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Tsinghua Science and Technology 2017年第5期22卷 489-498页

作者： Ke niu Xiaoyuan Yang Yingnan Zhang Key Laboratory of Network & Information Security of PAP Engineering College of PAP

A novel reversible data hiding algorithm for H.264/AVC videos is proposed. Histogram Shifting （HS） of motion vector values is used efficiently in reversible data hiding to embed data. By designating a specific decoded reference frame, the distortion accumulation effects due to modification of the motion vectors is overcome. All the extracted information can be recovered without loss of the original compressed video carrier. The experimental results show that the proposed algorithm is simple, has higher capacity and invisibility than other existing schemes, and can adjust the relationship between capacity and invisibility according to embedded load.

关键词： reversible video data hiding H.264/AVC motion vector histogram modification modified referenceframe

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Recycling Spent LiCoO_(2)Battery as a High-efficient Lithiumdoped Graphitic Carbon Nitride/Co_(3)O_(4)Composite Photocatalyst and Its Synergistic Photocatalytic Mechanism

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Energy & Environmental Materials 2023年第2期6卷 45-53页

作者： Bo niu Jiefeng Xiao Zhenming Xu School of Environmental Science and Engineering Shanghai Jiao Tong UniversityShanghai 200240China

The ever-increasing quantity of spent lithium-ion batteries(LIBs)is both a potential environmental pollutant and a valuable *** spent LIBs recycling mainly aimed at the separation of valuable *** issues still exist in these processes such as high energy consumption and complex separation *** study avoided element separation and proposed a facile approach to transform spent LiCoO_(2) electrode into a lithium(Li)-doped graphitic carbon nitride(g-C_(3)N_(4))/Co_(3)O_(4) composite photocatalyst through one-pot in situ thermal *** the thermal process,melamine served as the reductant for LiCoO_(2) decomposition and the raw material for g-C_(3)N_(4) *** was in situ doped in g-C_(3)N_(4) and the generated Co_(3)O_(4) was in situ integrated,forming a Li-doped g-C_(3)N_(4)/Co_(3)O_(4) composite *** special composite exhibited an enhanced photocatalytic performance,and its photocatalytic H2 production and RhB degradation rates were 8.7 and 6.8 times higher than those of g-C_(3)N_(4).The experiments combined with DFT calculation revealed that such enhanced photocatalytic efficiency was ascribed to the synergy effect of Li doping and Co_(3)O_(4) integrating,which extended the visible light absorption(450-900 nm)and facilitated the charge transfer and *** study transforms waste into a high-efficient catalyst,realizing high-valued utilization of waste and environmental protection.

关键词： composite photocatalyst environmental protection spent LIBs synergy mechanism waste utilization

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Support vector machine based machine learning method for GS 8QAM constellation classification in seamless integrated fiber and visible light communication system

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Science China(Information Sciences) 2020年第10期63卷 182-193页

作者： Wenqing niu Yinaer HA Nan CHI Key Laboratory for Information Science of Electromagnetic Waves (MoE) Fudan University

Visible light communication(VLC) network over optical fiber has become a potential candidate in ultra-high speed indoor wireless communication. To mitigate signal distortion accumulated in optical fiber and VLC channel, we present to utilize support vector machine(SVM) for constellation classification in two kinds of geometrically-shaped 8 QAM(quadrature amplitude modulation) seamless integrated fiber and VLC system. We introduce 4 sub-bands to simulate multi-user. Experimental results show that system performance can be significantly improved, and transmission at-2.5 dB m input optical power under 7%forward error correction(FEC) threshold can be realized employing Circular(7, 1) geometrically-shaped8 QAM and SVM. At overall capacity of 960 Mbps, Q-factor increases by up to 11.5 dB.

关键词： visible light communication VLC support vector machine SVM geometrically shaping GS VLC network constellation classification

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