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Stability of elliptic Harnack inequalities Dedicated to Professor Jia-an Yan on the Occasion of His 80th Birthday

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Science China Mathematics 2023年第10期66卷 2179-2190页

作者： Zhen-qing chen Department of Mathematics University of WashingtonSeattleWA 98195USA

We survey some recent progress in the study of stability of elliptic Harnack inequalities under form-bounded perturbations for strongly local Dirichlet forms on complete locally compact separable metric spaces.

关键词： elliptic Harnack inequality Green function metric doubling good doubling measure Dirichlet form relative capacity time change

The damage to model concrete gravity dams subjected to water explosions

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Defence Technology（防务技术） 2023年第9期27卷 119-137页

作者： Shang Ma Ye-qing chen Zhen-qing Wang Shu-tao Li qing Zhu Long-ming chen College of Aerospace and Civil Engineering Harbin Engineering UniversityHarbin150001China Institute of Defense Engineering AMSPLABeijing100036China

Over the past century,the safety of dams has gradually attracted attention from all *** on the dynamic response and damage evolution of dams under extreme loads is the basis of dam safety *** recent decades,scholars have studied the responses of dams under earthquake loads,but there is still much room for improvement in experimental and theoretical research on small probability loads such as *** this paper,a 50-m-high concrete gravity dam is used as a prototype dam,and a water explosion model test of a 2.5-m-high concrete gravity dam is *** water pressure and the acceleration response of the dam body in the test are *** pressure characteristics and dynamic response of the dam body are *** the dam damage test as an example,a numerical model of concrete gravity dam damage is established,and the damage evolution of the dam body is *** combining experiments and numerical simulations,the damage characteristics of the dam body under the action of different charge water explosions are *** integrity of the dam body is well maintained under the action of a small-quantity water explosion,and the dynamic response of the dam body is mainly caused by the shock *** the shock wave and the bubble pulsation cause the dam body to accelerate,and the peak acceleration of the dam body under the action of the bubble pulsation is only one percent of the peak acceleration of the dam body under the action of the shock *** subjected to explosions in large quantities of water,the dam body is seriously *** the action of a shock wave,the dam body produces a secondary acceleration response,which is generated by an internal interaction after the dam body is *** damage evolution process of the dam body under the action of a large-scale water explosion is analysed,and it is found that the shock wave pressure of the water explosion causes local damage to the dam body facing the ***

关键词： Underwater explosion Concrete gravity dam Model test Damage evolution

The Bipolar Quantum Drift-diffusion Model

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Acta Mathematica Sinica,English Series 2009年第4期25卷 617-638页

作者： Xiu qing chen Li chen School of Sciences Beijing University of Pos~s and Telecommunications Beijing 100876 P. R. China Department of Mathematical Sciences Tsinghua University Beijing 100084 P. R. China

A fourth order parabolic system, the bipolar quantum drift-diffusion model in semiconductor simulation, with physically motivated Dirichlet-Neumann boundary condition is studied in this paper. By semidiscretization in time and compactness argument, the global existence and semiclassical limit are obtained, in which semiclassieal limit describes the relation between quantum and classical drift-diffusion models, Furthermore, in the case of constant doping, we prove the weak solution exponentially approaches its constant steady state as time increases to infinity.

关键词： quantum drift-diffusion fourth order parabolic system weak solution semiclassical limit,exponential decay

Dynamical phase-field model of coupled electronic and structural processes

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npj Computational Materials 2022年第1期8卷 1223-1229页

作者： Tiannan Yang Long-qing chen Department of Materials Science and Engineering The Pennsylvania State UniversityUniversity ParkPA16802USA

Many functional and quantum materials derive their functionality from the responses of both their electronic and lattice subsystems to thermal,electric,and mechanical stimuli or *** we propose a dynamical phase-field model for predicting and modeling the dynamics of simultaneous electronic and structural processes and the accompanying mesoscale pattern evolution under static or ultrafast external *** an illustrative example of application,we study the transient dynamic response of ferroelectric domain walls excited by an ultrafast above-bandgap light *** discover a two-stage relaxational electronic carrier evolution and a structural evolution containing multiple oscillational and relaxational components across picosecond to nanosecond *** phase-field model offers a general theoretical framework which can be applied to a wide range of functional and quantum materials with interactive electronic and lattice orders and phase transitions to understand,predict,and manipulate their ultrafast dynamics and rich mesoscale evolution dynamics of domains,domain walls,and charges.

关键词： electronic structural phase

Weldability of 1000 MPa Grade Ultra-low Carbon Bainitic Steel

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Journal of Iron and Steel Research International 2016年第7期23卷 705-710页

作者： qing-mei JIANG Xiao-qiang ZHANG Li-qing chen Pipeline Department of China Petroleum Pipeline Engineering Corporation Langfang 065000 Hebei China State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 Liaoning China

Maximum hardness test in weld heat-affected zone（HAZ）,oblique Y-groove cracking test and mechanical property test of welding joint of 1 000 MPa grade ultra-low carbon bainitic steel were carried out,so as to research the weldability of the *** results show that the steel has lower cold cracking sensitivity,and preheating temperature of 100 ℃ can help completely eliminate cold cracks,generating good process *** increase of preheating temperature can reduce the hardening degree of heat-affected *** strength of welding joint decreases and hardness reduces when heat inputs increase,and excellent mechanical properties can be obtained when low welding heat inputs are *** lath bainites of different orientations combined with a few granular bainites that effectively split the original coarse austenite grains are the foundation of good properties.

关键词： ultra-low carbon bainitic steel weldability cold cracking microstructure mechanical property

Two alternative modes for diffuse pollution control in Wuhan City Zoo

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Journal of Environmental Sciences 2007年第9期19卷 1067-1073页

作者： chen qing-feng SHAN Bao-qing YIN cheng-qing HU cheng-xiao State Key Laboratory of Environmental Aquatic Chemistry Research Center for Eco-Environmental SciencesChinese Academy of Sciences Beijing 10085 China College of Resources and Environment Huazhong Agriculture University Wuhan 430050 China.

Pollution in urban zoos arises from diffuse and small point sources. However, its control has received little attention in past decades. Online and ofttine modes of ecological engineering technology were designed to control pollution from small point and diffuse sources in Wuhan City Zoo, China. Their characteristics and performances were investigated in sixteen runoff events from 2003 to 2005. The results showed that the two modes both improved runoff water quality and had high retention rates for water and pollutants. In the outflows, the event mean concentrations （EMCs） of total suspended solids （TSS）, chemical oxygen demand （COD）, total nitrogen （TN） and total phosphorus （TP） were reduced by 88%, 59%, 46% and 71% for the online mode, and those were 77%, 42%, 50% and 66% for the ofttine mode. The annual retention rates of pollutant loads for the online mode were 94.9%-98.5% in the three study years; those for the ofitine mode were 70.5%-86.4%. Based on calculation, the online mode was able to store the runoff of 66.7 mm rainfall completely, and the ofttine mode could store that of 31.3 mm rainfall. In addition, the online mode can provide an effective way for rainwater utilization and good habitats for aquatic wildlives, and has an excellent aesthetics value for recreationsal pastimes. The ofiline mode can save land resources and may be an effective and economical measure for diffuse pollution control in urban areas.

关键词： eutrophication runoff stormwater wetland zoo

Paleogeographic evolution of the Lower Yangtze region and the break of the “platform-slope-basin” pattern during the Late Ordovician

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Science China Earth Sciences 2018年第5期61卷 625-636页

作者： qing chen Junxuan FAN Linna ZHANG Xu chen CAS Key Laboratory of Economic Stratigraphy and Palaeogeography Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences Laboratory for Marine Geology Qingdao National Laboratory for Marine Science and Technology

Wide distribution of the black shales and diversification of the graptolite fauna in South China during the Late Ordovician resulted from its unique paleogeographic pattern, which was significantly affected by the paleogeographic evolution of the Lower Yangtze region. In the study, 120 Upper Ordovician sections from the Lower Yangtze region were collected, and a unified biostratigraphic framework has been applied to these sections to establish a reliable stratigraphic subdivision and correlation. Under the unified time framework, we delineate the distribution area of each lithostratigraphic unit, outline the boundary between the sea and land, and reconstruct the paleogeographic pattern for each graptolite zone. The result indicates that, with the uplift and expansion of the ‘Jiangnan Oldland' in the beginning of the late Katian, the oldland extended into the Yangtze Sea gradually from south to north, which finally separate the Jiangnan Slope and the Yangtze Platform. Consequently,the longstanding paleogeographic pattern of "platform-slope-basin" in South China was broken. The paleogeographic change led to sedimentary differentiation among the two sides of the ‘Jiangnan Oldland' during the Late Ordovician. This event also led to the closure of the eastern exit of the Upper Yangtze Sea, and formed a semi-closed, limited and stagnant environment for the development of the organic-rich black shales during the Late Ordovician. The major controlling factors of these paleogeographic changes in the Lower Yangtze region were not consistent from the Katian to the Hirnantian. In the late Katian, the sedimentary differentiation between the east and west sides mostly resulted from regional tectonic movement-the Kwangsian ***, during the Hirnantian, the whole Yangtze region became shallower, which was mostly influenced by the concentration of the Gondwana ice sheet and the consequent global sea level drop.

关键词： Lower Yangtze region Late Ordovician Paleogeography Platform-slope-basin Black shale

Comparison and integration of final electromagnetic stirring and thermal soft reduction on continuous casting billet

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Journal of Iron and Steel Research International 2021年第2期28卷 160-167页

作者： Yan-shen Han Wei Yan Jiang-shan Zhang Jun chen Wei-qing chen qing Liu State Key Laboratory of Advanced Metallurgy University of Science and Technology BeijingBeijing 100083China Xiangtan Iron&Steel Co. Ltd.of Hunan ValinXiangtan 411101HunanChina

Final electromagnetic stirring(F-EMS)and thermal soft reduction(TSR)are techniques that improve the inner quality of continuous casting billets,but they have rarely been applied *** application effects of F-EMS and TSR were compared,and a process integrating F-EMS and TSR was adopted for a billet continuous caster.A heat transfer model was established to calculate the thermal behavior of 82A tire cord steel *** locations of F-EMS and TSR were determined,followed by conducting a series of plant trials,involving F-EMS alone,TSR alone,and the integrated process of F-EMS and *** results showed that F-EMS or TSR could effectively improve the inner quality of the billet under their respective suitable working ***,F-EMS was found to be more helpful in terms of improving central segregation,while TSR tended to improve V-segregation,central porosity,and *** integration of F-EMS and TSR allowed the advantages of each technique to be utilized,thereby better improving the inner *** all the working conditions,82A steel billet showed optimum inner quality when the current of F-EMS was 240 A and the cooling intensity of TSR was 2.2 m^(3) h^(−1).These findings demonstrate that the integration of F-EMS and TSR is promising for application on continuous casting billets.

关键词： Billet continuous casting Final electromagnetic stirring Thermal soft reduction Central segregation Inner quality

Influence of austempering process on microstructures and mechanical properties of V-containing alloyed ductile iron

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Journal of Iron and Steel Research International 2018年第1期25卷 81-89页

作者： Jun-jun Cui Li-qing chen State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 Liaoning China College of Mechanical and Vehicle Engineering ShenyangInstitute of Technology Fushun 113122 Liaoning China

The influence of austempering time and vanadium addition on microstructure and mechanical properties of the alloyed ductile iron has been investigated. The 0.30 wt% V-containing and V-free alloyed ductile irons were firstly austenitized at 850 ℃ for 1 h and then austempered in a salt bath at 300 ℃ for 2, 3 and 4 h, respectively. For the 0.3 wt% V-containing alloyed ductile iron, the transformation product （ausferrite） was finer, and a small amount of martensite and a large amount of stable austenite were obtained after austempering for 2 h, while higher hardness and compressive strength of 62.8 HRC and 3000 MPa were achieved. For the V-free alloyed ductile iron, lower hardness and compressive strength were measured to be 56.8 HRC and 2320 MPa. As the austempering time increases, the amount of stable austenite decreases in the V-containing ductile iron, typically for the start of the second stage formation （retained austenite （γτ） →α ＋ carbide）. Based on this, it is assumed that the optimal processing window （OPW） was narrowed due to the addition of 0.30 wt% V as compared to the V-free ductile iron. When the hardness of 0.30 wt% V-alloyed ductile iron was higher than 59 HRC, the highest wear resist- ance was obtained. The mechanical cutting plays a dominant role in abrasive wear process.

关键词： Alloyed ductile iron Vanadium Austempering Microstructure Property Wear resistance