检索结果-南通市图书馆

Compressive Creep Behavior of TiC/AZ91D Magnesium-matrix Composites with Interpenetrating Networks

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2007年第2期23卷 207-212页

作者： Liqing CHEN Jinhua GUO Baohai YU Zongyi MA The State Key laboratory of Rolling and Automation Northeastern University Shenyang 110004 China Institute of Metal research Chinese Academy of Sciences Shenyang 110016 China

The 42.1 vol. pct TiC/AZ91D magnesium-matrix composites with interpenetrating networks were fabricated by in-situ reactive infiltration process. The compressive creep behavior of as-synthesized composites was investigated at temperature ranging from 673 to 723 K under loads of 95-108 MPa. For a comparative purpose,the creep behavior of the monolithic matrix alloy AZ91D was also conducted under loads of 15-55 MPa at 548-598 K. The creep mechanisms were theoretically analyzed based on the power-law relation. The results showed that the creep rates of both TiC/AZ91D composites and AZ91D alloy increase with increasing the temperature and load. The TiC/AZ91D composites possess superior creep resistance as compared with the AZ91D alloy. At deformation temperature below 573 K, the stress exponent n of AZ91D alloy approaches theoretical value of 5, which suggests that the creep process is controlled by dislocation climb. At 598 K, the stress exponentof AZ91D is close to 3, in which viscous non-basal slip deformation plays a key role in the process of creep deformation. However, the case differs from that of AZ91D alloy when the stress exponent n of TiC/AZ91D composites exceeds 9, which shows that there exists threshold stress in the creep process of the composites, similar to other types of composites. The average activation energies for the creep of the AZ91D alloy and TiC/AZ91D composites were calculated to be 144 and 152 k J/mol, respectively. The existence of threshold stress in the creep process of the composites leads to an increase in activation energy for creep.

关键词： Magnesium-matrix composites TiC/AZ91D Interpenetrating networks In-situ reactive infiltration Creep

Synthesis, Crystal Structure and Spectral Properties of [Ce(NO_3)_5(H_2O)_2]·2(Hphen)·(H_2O)

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Structural Chemistry 2004年第8期23卷 870-874页

作者：陈达贵程文旦张浩张永春 State Key laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter The Chinese Academy of Sciences Fuzhou Fujian 350002 ChinaGraduate School of the Chinese Academy of Sciences 100039 China State Key laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter The Chinese Academy of Sciences Fuzhou Fujian 350002 China

A novel complex [Ce(NO3)5(H2O)2]2(Hphen)(H2O) (phen =1,10-phenanthro-line) with formula C24H24CeN9O18 and Mr = 866.64 has been synthesized and structurally characterized by X-ray diffraction. It crystallizes in triclinic, space group P with a = 7.5534(2), b = 8.083(2), c = 25.8377(6) , = 86.847(1), = 89.937(1), = 86.981(1), V = 1572.94(6) 3, Dc = 1.830 g/cm3, F(000) = 866, m = 1.545 cm-1 and Z = 2. The final refinement gave R = 0.0486 and wR = 0.1278 for 4852 observed reflections with I > 2s(I). It consists of discrete [Ce-(NO3)5(H2O)2]2- anion, two Hphen+ cations and a lattice water molecule. In the compound, all of the five nitrates are bidentate, and the coordination of Ce(III) is 12. The photo-luminescence of this compound was also investigated.

关键词： cerium nitrate 1,10-phenanthroline crystal structure photoluminescence

Carbon sequestration of plantation in Beijing-Tianjin sand source areas

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Mountain Science 2018年第10期15卷 2148-2158页

作者： LIU Xiu-ping ZHANG Wan-jun CAO Jian-sheng YANG Bai CAI Yan-jiang Key laboratory of Agricultural Water Resources Hebei Key Laboratory of Agricultural Water-Saving Center for Agricultural Resources Research Institute of Genetics and Developmental Biology Chinese Academy of Sciences Environmental Sciences Division Oak Ridge National Laboratory Key laboratory of Mountain Environment Evolvement and Regulation Institute of Mountain Hazards and Environment Chinese Academy of Sciences

The Beijing-Tianjin Sand Source Control Project(BTSSCP), a national ecological restoration project, was launched to construct an ecological protection system in the Beijing-Tianjin sand source areas to reduce dust hazards. The carbon sequestration dynamics can be used to assess the ecological effects of an ecological restoration project. Here, we conducted vegetation and soil study to assess the carbon sequestration in the plantations with 10 years old stands in Beijing-Tianjin sand source areas. The results at the site scales indicated that the average net increase of plantation ecosystem carbon stock was 33.8 Mg C ha^(-1), with an annual increase rate of 3.38 Mg C ha^(-1) yr^(-1). The average net increase of carbon varied among regions, vegetation types, and forest management activities. Soil bulk density in the top soil decreased slightly after 10-year implementation of the project. Coniferous forests and shrubs are suitable plant species for sand source *** restoration in the plantations is a practical and feasible and promising approach for enhancing ecosystem carbon sequestration potential.

关键词： Afforestation Carbon sequestration Carbon density Forest management Restoration Sand source control

Compression Behavior and Failure Mechanisms of Bionic Porous NiTi Structures Built via Selective Laser Melting

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2023年第6期36卷 926-936页

作者： Xiaolong Zhang Yue Jiang Shupeng Wang Shuo Wang Ziqiang Wang Zhenglei Yu Zhihui Zhang Luquan Ren Key laboratory of Bionic Engineering Ministry of EducationJilin UniversityChangchun 130022China Luoyang Ship Material research Institute Luoyang 471023China

Inspired by the crystal microstructure of metals and the bamboo,the bionic porous NiTi structures with the porosities in the range of 75.8%–84.9%were built via selective laser melting(SLM).The compression behavior and the failure mechanisms of the porous NiTi structures were *** demonstrated an increase in the elastic modulus and ultimate strength when the porosity was decreased,from 3.06 to 7.66 GPa and from 34.1 to 147.6 MPa,*** relationship between the elastic modulus and the porosity obtained by the finite element analysis exhibited similar tendency with the experiment,and agreed well with the Gibson-Ashby model’s *** on the theoretical model above and the observation of the deformation processing,the plastic deformation behavior and failure mechanisms of the SLMed porous NiTi structures were analyzed.

关键词： Selective laser melting NiTi shape memory alloys Additive manufacturing Porous structure Bionic design

Charge transfer and bipolar charging of particles in a bubbling fluidized bed

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2021年第1期19卷 109-115页

作者： Mahshad Manafi Reza Zarghami Navid Mostoufi Multiphase Systems research laboratory School of Chemical EngineeringCollege of EngineeringUniversity of TehranP.O.Box 11155-4563TehranIran

Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on *** work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge separation)and their influence on hydrodynamic structures in a fluidized *** were performed with glass beads and polyethylene particles in a glass *** pressure fluctuations and net electrostatic charge of particles were measured during *** and short-time Fourier transforms were used to analyze pressure *** results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass *** charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime.A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge *** of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its *** longer fluidization times,the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium *** results well describe the effect of fluidization time on hydrodynamic structures.

关键词： Contact electrification Charge transfer Bipolar charging Pressure fluctuations Fluidization structures

Code Hop: physical layer error correction and encryption with LDPC-based code hopping

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2016年第10期59卷 121-135页

作者： Zhao CHEN Liuguo YIN Yukui PEI Jianhua LU Department of Electronic Engineering Tsinghua University Electronic Design Automation (EDA) laboratory Research Institute of Tsinghua University in Shenzhen School of Aerospace Tsinghua University

This paper proposes a novel scheme named Code Hop, which provides both information reliability and security using code hopping based on low-density parity-check(LDPC) codes. In contrast to traditional systems that perform error correction and encryption at different layers, Code Hop combines these two operations into a single step at physical layer, such that each plaintext message is jointly encoded and encrypted by a hopping parity-check matrix. According to a pseudo-random number generator(PRNG), the hopping matrix may rapidly switch among a sequence of LDPC parity-check matrices, which is randomly generated by a structured-random protograph expanding technique. Simulations show that reliable communication can be achieved by Code Hop with good error-correcting performance. In the meantime, Code Hop may improve the security of traditional systems such as GSM. Taking the A5/1 stream cipher used in GSM as the PRNG, it is shown that Code Hop is resistant to existing chosen-plaintext attacks that break A5/1 cipher already. Moreover, the security of Code Hop will be enhanced in the presence of channel errors as well.

关键词： physical layer security error correction data encryption low-density parity-check codes code hopping

MILD Combustion for Hydrogen and Syngas at Elevated Pressures

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Thermal Science 2014年第1期23卷 96-102页

作者： HUANG Mingming ZHANG Zhedian SHAO Weiwei XIONG Yan LEI Fulin XIAO Yunhan Key laboratory of Advanced Energy and Power Institute of Engineering ThermophysicsChinese Academy of Sciences research Center for Clean Energy and Power Chinese Academy of Sciences

As gas recirculation constitutes a fundamental condition for the realization of MILD combustion, it is necessary to determine gas recirculation ratio before designing MILD combustor. MILD combustion model with gas recirculation was used in this simulation work to evaluate the effect of fuel type and pressure on threshold gas recirculation ratio of MILD mode. Ignition delay time is also an important design parameter for gas turbine combustor, this parameter is kinetically studied to analyze the effect of pressure on MILD mixture ignition. Threshold gas recirculation ratio of hydrogen MILD combustion changes slightly and is nearly equal to that of 10 MJ/Nm3syngas in the pressure range of 1-19 atm, under the conditions of 298 K fresh reactant temperature and 1373 K exhaust gas temperature, indicating that MILD regime is fuel flexible. Ignition delay calculation results show that pressure has a negative effect on ignition delay time of 10 MJ/Nm3syngas MILD mixture, because OH mole fraction in MILD mixture drops down as pressure increases, resulting in the delay of the oxidation process.

关键词： MILD combustion Gas turbine combustor Syngas Gas recirculation ratio Ignition delay time

Investigation of system structure and information processing mechanism for cognitive skywave over-the-horizon radar

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Engineering and Electronics 2016年第4期27卷 797-806页

作者： Xia Wu Jianwen Chen Kun Lu Key laboratory for Radar Application Engineering Wuhan Institute of RadarWuhan 430019China Nanjing research Institute of Electronics Technology Nanjing 210039China

Based on the cognitive radar concept and the basic connotation of cognitive skywave over-the-horizon radar（SWOTHR）, the system structure and information processingmechanism about cognitive SWOTHR are researched. Amongthem, the hybrid network system architecture which is thedistributed configuration combining with the centralized cognition and its soft/hardware framework with the sense-detectionintegration are proposed, and the information processing framebased on the lens principle and its information processing flowwith receive-transmit joint adaption are designed, which buildand parse the work law for cognition and its self feedback adjustment with the lens focus model and five stages informationprocessing sequence. After that, the system simulation andthe performance analysis and comparison are provided, whichinitially proves the rationality and advantages of the proposedideas. Finally, four important development ideas of futureSWOTHR toward ＂high frequency intelligence information processing system＂ are discussed, which are scene information fusion, dynamic reconfigurable system, hierarchical and modulardesign, and sustainable development. Then the conclusion thatthe cognitive SWOTHR can cause the performance improvement is gotten.

关键词： cognitive radar skywave over-the-horizon radar system structure intelligence information processing information fusion target detection

Destruction of methylphosphonic acid in a supercritical water oxidation bench-scale double wall reactor

在线全文

学校读者我要写书评

暂无评论

Journal of Environmental Sciences 2011年第4期23卷 545-552页

作者： Bambang Veriansyah Eun-Seok Song Jae-Duck Kim Supercritical Fluid research laboratory Korea Institute of Science and Technology (KIST) 39-1 Hawolgok-dong Seoungbuk-gu Seoul 136-791 Korea

The destruction of methylphosphonic acid （MPA）, a final product by hydrolysis/neutralization of organophosphorus agents such as sarin and VX （O-ethyl S-[2-（diisopropylamino）ethyl] methylphosphonothionate）, was investigated in a a bench-scale, continuous concentric vertical double wall reactor under supercritical water oxidation condition. The experiments were conducted at a temperature range of 450–600°C and a fixed pressure of 25 MPa. Hydrogen peroxide was used as an oxidant. The destruction efficiency （DE） was monitored by analyzing total organic carbon （TOC） and MPA concentrations using ion chromatography on the liquid effluent samples. The results showed that the DE of MPA up to 99.999% was achieved at a reaction temperature of 600°C, oxygen concentration of 113% storichiometric requirement, and reactor residence time of 8 sec. On the basis of the data derived from experiments, a global kinetic rate equation for the DE of MPA and DE of TOC were developed by nonlinear regression analysis. The model predictions agreed well with the experimental data.

关键词： supercritical water oxidation destruction efficiency methylphosphonic acid reaction kinetic nonlinear regression