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Some embedding theorems for W～(1,p)(Ω, H～n)

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Applied Mathematics(A Journal of Chinese Universities) 2010年第1期25卷 85-92页

作者： jia Gao zhang Guo-qing College of Science University of Shanghai for Science and Technology Shanghai 200090 China

For the maps on the Heisenberg group target, we prove a Poincare type inequality. Applying this Poincare type inequality, we obtain the corresponding versions of Sobolev and Rellich embedding theorems.

关键词： Heisenberg group HSlder continuity embedding theorem.

Estimation of fracture density and orientation from azimuthal elastic impedance difference through singular value decomposition

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Petroleum Science 2021年第6期18卷 1675-1688页

作者： Lin Li Guang-Zhi zhang Jun-Zhou Liu Lei Han jia-jia zhang School of Geosciences China University of Petroleum(East China)QingdaoShandong 266580China Sinopec Exploration and Production Research Institute Beijing100083China

Accurate estimation of fracture density and orientation is of great significance for seismic characterization of fractured ***,we propose a novel methodology to estimate fracture density and orientation from azimuthal elastic impedance(AEI)difference using singular value decomposition(SVD).Based on Hudson's model,we first derive the AEI equation containing fracture density in HTI media,and then obtain basis functions and singular values from the normalized AEI difference utilizing *** shows that the basis function changing with azimuth is related to fracture orientation,fracture density is the linearly weighted sum of singular values,and the first singular value contributes the most to fracture ***,we develop an SVD-based fracture density and orientation inversion approach constrained by smooth prior elastic *** example shows that fracture density and orientation can be stably estimated,and the correlation coefficient between the true value and the estimated fracture density is above 0.85 even when an S/N ratio of *** data example shows that the estimated fracture orientation is consistent with the interpretation of image log data,and the estimated fracture density reliably indicates fractured gas-bearing reservoir,which could help to guide the exploration and development of fractured reservoirs.

关键词： Singular value decomposition HTI media Azimuthal elastic impedance inversion Fracture density Fracture orientation

A Study on the Transport Process in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells

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Journal of Thermal Science 2011年第5期20卷 449-453页

作者： Zetao Tan Li jia Zhuqian zhang Department of Power Engineering Beijing Jiaotong University

Gas diffusion layer(GDL) plays a great important role in proton exchange membrane fuel cell(PEMFC).Water transport mechanism in GDL is still not *** the present study,an ex-situ transparent setup is built to visualize the transport phenomena and to measure the threshold pressure of water in GDL at different *** is found that the relationship between the breakthrough pressure and the temperature is nearly linear(*** pressure decreases linearly with the increase of temperature).To avoid the problems faced by the continuum models,the pore network model is developed to simulate the liquid water transport through the carbon paper.A uniform pressure boundary condition is used in simulation and the results are similar to the ones obtained in the *** reason is that the contact angle and surface tension coefficient of water in GDLs change accordingly with the change of temperature.

关键词： PEMFC gas diffusion layer pore network model water breakthrough temperature

Influence of pressure disturbance wave on dynamic response characteristics of liquid film seal for multiphase pump

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Petroleum Science 2024年第3期21卷 2048-2065页

作者： Qing-Ping Li Jin-Ya zhang jia-Xiang zhang Yong-Xue zhang CNOOC Research Institute Company Limited Beijing100028China State Key Laboratory of Natural Gas Hydrate Beijing100028China College of Mechanical and Transportation Engineering China University of PetroleumBeijing2249China

Slug flow or high GVF(Gas Volume Fraction)conditions can cause pressure disturbance waves and alternating loads at the boundary of mechanical seals for multiphase pumps,endangering the safety of multiphase pump *** mechanical seal model is simplified by using periodic boundary conditions and numerical calculations are carried out based on the Zwart-Gerber-Belamri cavitation ***(User Define Function)programs such as structural dynamics equations,alternating load equations,and pressure disturbance equations are embedded in numerical calculations,and the dynamic response characteristics of mechanical seal are studied using layered dynamic mesh *** results show that when the pressure disturbance occurs at the inlet,as the amplitude and period of the disturbance increase,the film thickness gradually *** the fundamental reason for the hysteresis of the film thickness change is that the pressure in the high-pressure area cannot be restored in a timely *** maximum value of leakage and the minimum value of axial velocity are independent of the disturbance period and determined by the disturbance *** mutual interference between enhanced waves does not have a significant impact on the film thickness,while the front wave in the attenuated wave has a promoting effect on the subsequent film thickness changes,and the fluctuation of the liquid film cavitation rate and axial velocity under the attenuated wave condition deviates from the initial *** with pressure disturbance conditions,alternating load conditions have a more significant impact on film thickness and *** actual operation,it is necessary to avoid alternating load conditions in multiphase pump mechanical seals.

关键词： Multiphase pump Liquid film seal Pressure disturbance wave Dynamic response characteristics

Tailoring microenvironment for efficient CO_(2)electroreduction through nanoconfinement strategy

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Nano Research 2024年第9期17卷 7880-7899页

作者： Lulu Chen Minhan Li jia-Nan zhang Key Laboratory of Advanced Energy Catalytic and Functional Materials Preparation Country College of Materials Science and EngineeringZhengzhou UniversityZhengzhou 450001China

The electrocatalytic conversion of CO_(2)to produce fuels and chemicals holds great promise,not only to provide an alternative to fossil feedstocks,but also to use renewable electricity to convert and recycle the greenhouse gas CO_(2)to mitigate climate ***,the selectivity and reaction rates for the conversion of CO_(2)into desirable carbon-based products,especially multicarbon products with high added value,are still insufficient for commercial applications,which is attributed to insufficiently favourable microenvironmental conditions in the vicinity of the *** construction of catalysts/electrodes with confined structures can effectively improve the reaction microenvironment in the vicinity of the electrodes and thus effectively direct the reaction towards the desired *** this review,we firstly introduce the effects of the microenvironment at the electrode-electrolyte interface including local pH,local intermediate concentration,and local cation concentration on CO_(2)reduction reaction(CO_(2)RR)as well as the mechanism of action,and then shed light on the microenvironmental modulation within the confined space,and finally and most importantly,introduce the design strategy of CO_(2)RR catalyst/electrode based on the confinement effect.

关键词： CO_(2)reduction reaction microenvironment confinement effect catalyst design

Control of mould level fluctuation through the modification of steel composition

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International Journal of Minerals,Metallurgy and Materials 2013年第2期20卷 138-145页

作者： Yang Li Xiao-huan zhang Peng Lan jia-quan zhang School of Metallurgical and Ecological Engineering University of Science and Technology Beijing

Periodic mould level fluctuation （MLF） during slab casting is a bottleneck for upgrading the surface quality and casting speed especially for hypoperitectic （HP） or ultralow carbon steels. The uneven growth of the initially solidified shell is verified to be one of the important inducements to MLF due to related unsteady bulging in the secondary cooling zone. It is shown that the solidification mode of steels and the contraction behavior can be modified through chemical composition optimization within given composition limits, For high strength low alloy （HSLA） steels, the actual peritectic points calculated by Thermo-Calc software may change remarkably with the slight variations of alloying element contents. Accordingly, the narrow limit of chemical composition of HP steels through optimization is proven to be one of the effective factors to control the popular MLF phenomenon during slab casting.

关键词： low carbon steel continuous casting solidification composition optimization

Distributed collaborative complete coverage path planning based on hybrid strategy

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Journal of Systems Engineering and Electronics 2024年第2期35卷 463-472页

作者： zhang jia DU Xin DONG Qichen XIN Bin School of Automation Beijing Institute of TechnologyBeijing 100081China National Key Laboratory of Autonomous Intelligent Unmanned Systems Beijing Institute of TechnologyBeijing 100081China

Collaborative coverage path planning(CCPP) refers to obtaining the shortest paths passing over all places except obstacles in a certain area or space. A multi-unmanned aerial vehicle(UAV) collaborative CCPP algorithm is proposed for the urban rescue search or military search in outdoor *** to flexible control of small UAVs, it can be considered that all UAVs fly at the same altitude, that is, they perform search tasks on a two-dimensional plane. Based on the agents’ motion characteristics and environmental information, a mathematical model of CCPP problem is established. The minimum time for UAVs to complete the CCPP is the objective function, and complete coverage constraint, no-fly constraint, collision avoidance constraint, and communication constraint are considered. Four motion strategies and two communication strategies are designed. Then a distributed CCPP algorithm is designed based on hybrid strategies. Simulation results compared with patternbased genetic algorithm(PBGA) and random search method show that the proposed method has stronger real-time performance and better scalability and can complete the complete CCPP task more efficiently and stably.

关键词： multi-agent cooperation unmanned aerial vehicles(UAV) distributed algorithm complete coverage path planning(CCPP)

Contact binaries at different evolutionary stages

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Research in Astronomy and Astrophysics 2020年第10期20卷 229-248页

作者： Sheng-Bang Qian Li-Ying Zhu Liang Liu Xu-Dong zhang Xiang-Dong Shi jia-jia He jia zhang Yunnan Observatories Chinese Academy of SciencesKunming 650216China School of Physics and Astronomy Yunnan UniversityKunming 650091China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of SciencesKunming 650216China Center for Astronomical Mega-Science Chinese Academy of SciencesBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China

Contact binaries consist of two strongly interacting component stars where they are filling their critical Roche lobes and sharing a common *** of them are main-sequence stars,but some of them are post main-sequence *** are good astrophysical laboratories for studying several problems such as the merging of binary stars,evolution of the common envelope,the origin of luminous red nova outbursts and the formation of rapidly rotating single stars with possible planetary systems.A large number of contact binary candidates were detected by several photometric surveys around the world and many of them were observed by the LAMOST spectroscopic *** on follow-up observations,the evolutionary states and geometrical structures of some systems were understood *** this review,we will introduce and catalog new stellar atmospheric parameters(i.e.,the effective temperature(Teff),the gravitational acceleration(log(g)),metallicity([Fe/H])and radial velocity(Vr))for 9149 EW-type contact binaries that were obtained based on low-and medium-resolution spectroscopic surveys of *** we will focus on several groups of contact binary stars,i.e.,marginal contact binary systems,deep and low-mass ratio contact binary stars,binary systems below the short-period limit of contact binaries and evolved contact *** contact binaries are at the beginning of the contact stage,while deep and low-mass ratio contact binary stars are at the final evolutionary stage of tidally locked *** statistical relations including the period-temperature relation are determined well by applying LAMOST data and their formation and evolutionary states are *** period-color relation of M-type binaries reveals that there are contact binaries below the short-period *** for and investigating contact binaries near and below this limit will help us to understand the formation of contact binary systems and a new prediction for the short-period l

关键词： binaries:eclipsing stars:late-type stars:low-mass stars:formation stars:evolution

Density-Functional Theories for Polyelectrolyte Systems

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Chinese Journal of Polymer Science 2024年第9期42卷 1302-1312,I0006页

作者： jia-Wei zhang Yu-Hang zhang Bao-Hui Li Qiang Wang School of Physics Nankai UniversityTianjin90001China Department of Chemical and Biological Engineering Colorado State University1370 Campus DeliveryFort CollinsCO80523-1370USA

Polymer density-functional theories(PDFTs)have distinct advantages in the study of polyelectrolyte(PE)systems over experiments and molecular *** we give an introductory review of some PDFTs recently developed for PE *** start with a general formalism of PDFTs and its relation to the widely used polymer self-consistent field theory(SCFT),then explain the various correlations that are neglected in SCFT but can be accounted for in PDFTs,including those due to the excluded-volume interaction and chain connectivity of uncharged polymers,the electrostatic correlations of small ions,and the chain correlations in *** also list some applications of PDFTs for PE systems,and finally give some perspectives on future *** hope that our review can attract more researchers to apply and further develop PDFTs as a promising class of theoretical and computational tools.

关键词： Polymer density-functional theories Polyelectrolytes Correlations