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Aging assessment of large generator insulation based on PD measurements

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Progress in Natural Science:Materials International 2005年第11期15卷 1035-1043页

作者： YUE Bo, CHEN xiaolin, CHENG Yonghong and xiE Hengkun (state key laboratory of Electrical Insulation and Power Equipment, xi'an Jiaotong university, xi'an 710049, china Graduate School at Shenzhen, Tsinghua university, Shenzhen 518055, china Department of Electrical Engineering, Tsinghua university, Beijing 100084, china) state key laboratory of Electrical Insulation and Power Equipment Xi'an Jiaotong University Xi'an 710049 China Graduate School at Shenzhen Tsinghua University Shenzhen 518055 China Department of Electrical Engineering Tsinghua University Beijing 100084 China

The statistical parameters of phase resolved partial discharge (PD) distribution and ultra-wideband (UWB) characteristics of PD pulse are proposed for aging assessment of large generator insulation. Multi-stress aging tests of the model generator stator bar specimens were performed and PD measurements were conducted using both digital PD detector with frequency ranging from 40 kHz to 400 kHz and UWB PD detector with bandwidth from 10 MHz to 3 GHz at different aging stages. The test results show that the skewness and UWB frequency characteristics of PD can be taken as the characterization parameters for aging assessment of generator insulation. Furthermore, the measurement results of real generator stator bars show that these methods based on statistical parameters and UWB characteristics of PD are prospective for aging assessment and residual lifetime estimation of large generator stator insulation.

关键词： partial discharge stator insulation multi-stress accelerated aging statistical parameters ultra-wideband aging assessment.

Experimental Investigation and Numerical Simulation of the Grain Size Evolution during Isothermal Forging of a TC6 Alloy

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Journal of Materials Science & Technology 2005年第2期21卷 155-160页

作者： Miaoquan LI, Shankun XUE, Aiming xiONG and Shenghui CHEN state key laboratory of Solidification Processing, School of Materials Science and Engineering, Northwestern Polytechnical university, xi’an 710072, china Lab. of Solidification Proc. Sch. of Mat. Sci. and Eng. Northwestern Polytech. Univ. Xi'an 710072 China

Hot compression was conducted at a Thermecmaster-Z simulator, at deformation temperatures of 800-1040℃, with strain rates of 0.001-50 s-1 and height reduction of 50%. Grain size of the prior α phase was measured with a Leica LABOR-LUX12MFS/ST microscope to which QUANTIMET 500 software for image analysis for quantitative metallography was linked. According to the present experimental data, a constitutive relationship for a TC6 alloy and a model for grain size of the prior a phase were established based on the Arrhenius' equation and the Yada's equation, respectively. By finite element (FE) simulation, deformation distribution was determined for isothermal forging of a TC6 aerofoil blade at temperatures of 860-940℃ and hammer velocities of 9-3000.0 mm/min. Meanwhile, the grain size of the prior α phase is simulated during isothermal forging of the TC6 aerofoil blade, by combining FE outputs with the present grain size model. The present results illustrate the grain size and its distribution in the prior α phase during the isothermal forging of the TC6 aerofoil blade. The simulated results show that the height reduction, deformation temperature, and hammer velocity have significant effects on distribution of the equivalent strain and the grain size of the prior α phase.

关键词： Titanium alloy Isothermal forging Grain size Model Finite element (FE) simulation

Phase-selection and metastable phase formation in highly undercooled eutectic Ni78.6Si21.4alloys

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Progress in Natural Science:Materials International 2006年第3期16卷 287-291页

作者： LU Yiping, YANG Gencang, YANG Changlin, WANG Haipeng and ZHOU Yaohe (state key laboratory of Solidification Processing, Northwestern Polytechnical university, xi'an 710072, china Department of Applied Physics, Northwestern Polytechnical university, xi'an 710072, china) state key laboratory of Solidification Processing Northwestern Polytechnical University Xi'an 710072 China Department of Applied Physics Northwestern Polytechnical University Xi' an 710072 China

A large undercooling (250 K) was achieved in eutectic Ni78.6 Si21.4 melt by the combination of molten-glass denucleation and cyclic superheating. The metastable phase formation process in the bulk undercooled eutectic Ni78.6 Si21.4 melts was investigated. With the increase of undercooling, different metastable phases form in eutectic Ni78.6 Si21.4 melts and part of these metastable phases can be kept at room temperature through slow post-solidification. Under large undercooling, the metastable phases β2-Ni3Si, Ni31Si12 and Ni3Si2 were identified. Especially, the Ni3Si2 phase was obtained in eutectic Ni78.6 Si21.4 alloy for the first time. Based on the principle of free energy minimum and transient nucleation theory, the solidification behavior of melts was analyzed with regard to the metastable phase formation when the melts were in highly undercooled state.

关键词： undercooling molten-glass metastable phase rapid solidification.

Chosen Ciphertext Secure Identity-Based Broadcast Encryption in the Standard Model

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Journal of Shanghai Jiaotong university(Science) 2011年第6期16卷 672-676页

作者：孙瑾胡予濮张乐友 key laboratory of Computer network and Information Security Xidian University Department of Application Mathematics Xi'an University of Technology

To give concurrent consideration both the efficiency and the security(intensity of intractable problem) in the standard model,a chosen ciphertext secure identity-based broadcast encryption is *** the chosen ciphertext security model,by using identity(ID) sequence and adding additional information in ciphertext,the self-adaptive chosen identity security(the full security) and the chosen ciphertext security are gained *** reduction of scheme's security is the decisional bilinear Diffie-Hellman(BDH) intractable assumption,and the proof of security shows that the proposed scheme is indistinguishable against adaptive chosen ciphertext attacks in the standard model under the decisional BDH intractable *** the security level is improved,and it is suitable for higher security environment.

关键词： the standard model provably secure broadcast encryption the chosen ciphertext security the self-adaptive chosen identity security

Responses of growth performance,antioxidant function,small intestinal morphology and mRNA expression of jejunal tight junction protein to dietary iron in yellow-feathered broilers

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Journal of Integrative Agriculture 2024年第4期23卷 1329-1337页

作者： Kaiwen Lei Hao Wu Jerry W Spears xi Lin xi Wang Xue Bai Yanling Huang key laboratory of Animal Science of state Ethnic Affairs Commission Southwest Minzu UniversityChengdu 610041China key laboratory of Qinghai-Tibetan Plateau Animal Genetic Resource Reservation and Utilization Southwest Minzu UniversityChengdu 610041China Department of Animal Science North Carolina State UniversityRaleighNC 27695-7621USA

This study aimed to investigate the dose-effect of iron on growth performance,antioxidant *** morphology,and mRNA expression of jejunal tight junction protein in 1-to21-d-old yellow-feathered broilers.A total of 7201-d-old yellow-feathered maleb roilers were allocated to 9 treatments with 8 replicate cages of 10 birds per *** dietary treatments were consisted of a basal diet(contained 79.6 mg Fe kg^(-1))supplemented with 0,20,40,60,80,160,320,640,and 1,280 mg Fe kg^(-1)in the form of FeSO_(4)·7H_(2)*** with the birds in the control group,birds supplemented with 20mg Fe kg^(-1)had higher average daily gain(ADG)(Pxidative stress,disrupted intestinal morphology,and reduced mRNA expression of jejunal tight junction protein.

关键词： iron yellow-feathered broiler antioxidant function intestinal morphology tight junction protein

Oxidation Protective C/SiC/Si-SiC Multilayer Coating for Carbon/Carbon Composites Applying at 1873 K

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Journal of Materials Science & Technology 2010年第12期26卷 1139-1142页

作者： Yulei Zhang,Hejun Li,xinfa Qiang and Kezhi Li C/C Composites Research Center,state key laboratory of Solidification Processing,Northwestern Polytechnical university,xi an 710072,china C/C Composites Research Center State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi(an 710072 China

A C/SiC/Si-SiC multilayer coating for protecting carbon/carbon （C/C） composites against oxidation was prepared by slurry and pack cementation. X-ray diffraction （XRD） and energy dispersive spectroscopy （EDS） analysis showed that the inner coating obtained from the slurry and pack cementation was a C/SiC gradient layer acting as bonding layer, and the exterior coating formed in the second pack cementation was a Si-SiC double phase coating. Oxidation tests at 1873 K in air showed that the coating exhibited excellent oxidation protective ability and thermal shock resistance. The coating could effectively protect C/C composites from oxidation at 1873 K in air for 170 h and undergo the thermal cycling between 1873 K and room temperature for 8 cycles. The weight loss of the coated C/C composites is due to the formation of cracks and holes in the coating and the volatilization of SiO2 glass at high temperature.

关键词： Carbon/carbon composites Oxidation Coating

Numerical Investigation of Developing Turbulent Flow in a Helical Square Ductwith Large Curvature

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Journal of Thermal Science 2001年第1期10卷 1-6页

作者： Gao Hui,Guo Liejin (state key laboratory of Multiphase Flow in Power Engineering, xi’an Jiaotong university, xi’an 710049, china ) state key laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an China

A fully elliptic numerical study has been carried out to investigate the three-dimensional turbulent developing flow in a helical square duct with large curvature. A two-layer zonal model is proposed and used, in which the whole region is divided into a viscosity-affected near wall layer and a fully turbulent region. A DSM closure is applied in the former, and a one-equation model is solved in the latter. The results presented in this paper cover a Reynolds number range of (l- 10) x 104. The development of flow is found to be dominated by radial pressure gradient and Dean-type secondary motion. The distribution of Reynolds stresses in fully developed flow exhibit a complex pattern of turbulence anisotropy The development of peripherally averaged friction factor and the distribution of local friction factor in fully developed flow are given and discussed.

关键词： curved pipe developing flow turbulence model numerical simulation.

Pilot-aided channel estimation for CDD-OFDM systems

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Science china(Information Sciences) 2010年第2期53卷 379-389页

作者： FAN JianCun , YIN QinYe & WANG WenJie MOE key laboratory for Intelligent networks and network Security, Institute of Information Engineering, xi’an Jiaotong university, xi’an 710049, china MOE key laboratory for Intelligent networks and network Security Institute of Information Engineering Xi’an Jiaotong University Xi’an China

Cyclic delay diversity (CDD) is a low-complexity transmit diversity technique for coded orthogonal frequency division multiplexing (OFDM), which transforms a multiple-input channel into an equivalent singleinput channel with increased frequency selectivity and provides additional frequency diversity. However, it makes channel estimation more difficult due to the increased frequency selectivity. In this paper, focusing on the direct estimation of the equivalent single-input channel for CDD-OFDM systems, a cyclic cross-correlation channel estimation method based on the equispaced constant-modulus pilot structure is first proposed. Using the statistical parameters of the channel and noise derived by the cyclic cross-correlation channel estimation, an improved channel estimation method based on the Wiener filter is proposed to reduce the estimation error further. Lastly, computation simulations are given to demonstrate the effectiveness of two proposed channel estimation methods for CDD-OFDM systems.

关键词： channel estimation cyclic delay diversity OFDM systems cyclic cross-correlation Wiener filter

On power allocation for a cognitive radio network with hybrid spectrum sharing

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Science china(Information Sciences) 2011年第11期54卷 2425-2434页

作者： ZHANG Jing 1,2,3 & ZHU HongBo 1 1 key laboratory of Wireless Communications of Jiangsu Province,Nanjing university of Posts & Telecommunications,Nanjing 210003,china 2 College of Electronic Science & Engineering,Nanjing university of Posts & Telecommunications,Nanjing 210003,china 3.state key laboratory of Millimeter Waves,Nanjing 210096,china key laboratory of Wireless Communications of Jiangsu Province Nanjing University of Posts & Telecommunications Nanjing China College of Electronic Science & Engineering Nanjing University of Posts & Telecommunications Nanjing China state key laboratory of Millimeter Waves Nanjing China

In this study we propose a hybrid spectrum sharing scheme based on power control by combining Overlay with Underlay schemes,to improve radio spectrum *** the scheme,the secondary users dynamically switch their operational states between Overlay and Underlay according to the spectrum *** the dynamics of the primary network is first modeled with a discrete-state Markov process to find the time fraction of secondary users in the Overlay state and that in the Underlay state,which leads to the capacity model of the hybrid spectrum sharing *** the criterion of maximizing capacity,the power allocation of the cognitive network is researched and the optimum power allocation for secondary users is *** a result,the maximum achievable capacity of the cognitive network is *** are given to prove the analysis *** and simulated results indicate that hybrid spectrum sharing based on power control provides a higher capacity than single Overlay and Underlay systems for the cognitive network,i.e.,hybrid spectrum sharing can further improve radio spectrum efficiency.

关键词： cognitive radio network hybrid spectrum sharing primary network dynamics power allocation achievable capacity