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Highly accurate symplectic element based on two variational principles

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Acta Mechanica Sinica 2018年第1期34卷 151-161页

作者： Guanghui Qing jia tian College of Aeronautical Engineering Civil Aviation University of China

For the stability requirement of numerical resultants, the mathematical theory of classical mixed methods are relatively complex. However, generalized mixed methods are automatically stable, and their building process is simple and straightforward. In this paper, based on the seminal idea of the generalized mixed methods, a simple, stable, and highly accurate 8-node noncompatible symplectic element(NCSE8) was developed by the combination of the modified Hellinger-Reissner mixed variational principle and the minimum energy principle. To ensure the accuracy of in-plane stress results, a simultaneous equation approach was also suggested. Numerical experimentation shows that the accuracy of stress results of NCSE8 are nearly the same as that of displacement methods, and they are in good agreement with the exact solutions when the mesh is relatively fine. NCSE8 has advantages of the clearing concept, easy calculation by a finite element computer program, higher accuracy and wide applicability for various linear elasticity compressible and nearly incompressible material problems. It is possible that NCSE8 becomes even more advantageous for the fracture problems due to its better accuracy of stresses.

关键词： Modified H-R mixed variational principle Partial-mixed element Noncompatible symplectic element Finite element method Nearly incompressible material

More on half-wormholes and ensemble averages

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Communications in Theoretical Physics 2023年第9期75卷 1-21页

作者： jia tian Yingyu Yang Kavli Institute for Theoretical Sciences(KITS) University of Chinese Academy of Science100190 BeijingChina

We continue our study Half-Wormholes and Ensemble Averages about the half-wormhole *** generalizing the original proposal of the half-wormhole,we propose a new way to detect *** crucial idea is to decompose the observables into self-averaged sectors and non-self-averaged *** find the contributions from different sectors have interesting statistics in the semi-classical *** particular,dominant sectors tend to condense and the condensation explains the emergence of half-wormholes and we expect that the appearance of condensation is a signal of possible bulk *** also initiate the study of multi-linked half-wormholes using our approach.

关键词： half-wormholes factorization problem quantum gravity ensemble averages SYK

Notes on index of quantum integrability

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Communications in Theoretical Physics 2021年第5期73卷 1-9页

作者： jia tian Jue Hou Bin Chen School of Physics and State Key Laboratory of Nuclear Physics and Technology Peking UniversityNo.5 Yiheyuan RdBeijing 100871China Center for High Energy Physics Peking UniversityNo.5 Yiheyuan RdBeijing 100871China Collaborative Innovation Center of Quantum Matter No.5 Yiheyuan RdBeijing 100871China

A quantum integrability index was proposed in Komatsu et al(2019 SciPost Phys.7065).It systematizes the Goldschmidt and Witten's operator counting argument(Goldschmidt and Witten 1980 ***.B 91392)by using the conformal *** this work we compute the quantum integrability indexes for the symmetric coset models SU(N)/SO(N)and SO(2N)/SO(N)×SO(N).The indexes of these theories are all non-positive except for the case of SO(4)/SO(2)×SO(2).Moreover we extend the analysis to the theories with fermions and consider a concrete theory:the CP~N model coupled with a massless Dirac *** find that the indexes for this class of models are non-positive as well.

关键词： integrability quantum index coset models

Deformed integrable models from holomorphic Chern-Simons theory

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Science China(Physics,Mechanics & Astronomy) 2022年第10期65卷 53-74页

作者： Yi-Jun He jia tian Bin Chen School of Physics Peking UniversityBeijing 100871China Collaborative Innovation Center of Quantum Matter Beijing 100871China Center for High Energy Physics Peking UniversityBeijing 100871China Kavli Institute for Theoretical Sciences(KITS) University of Chinese Academy of SciencesBeijing 100190China

We study the approaches to two-dimensional integrable field theories via a six-dimensional(6 D) holomorphic Chern-Simons theory defined on twistor space. Under symmetry reduction, it reduces to a 4 D Chern-Simons theory, while under solving along fibres it leads to a four-dimensional(4 D) integrable theory, the anti-self-dual Yang-Mills or its generalizations. From both 4 D theories, various two-dimensional integrable field theories can be obtained. In this work, we try to investigate several twodimensional integrable deformations in this framework. We find that the λ-deformation, the rational η-deformation, and the generalized λ-deformation can not be realized from the 4 D integrable model approach, even though they could be obtained from the 4 D Chern-Simons theory. The obstacle stems from the incompatibility between the symmetry reduction and the boundary conditions. Nevertheless, we show that a coupled theory of the λ-deformation and the η-deformation in the trigonometric description could be obtained from the 6 D theory in both ways, by considering the case that(3, 0)-form in the 6 D theory is allowed to have zeros.

关键词： integrable systems gauge field theories classical field theories

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Study of Surface Cell Madelung Constant and Surface Free Energy of Nanosized Crystal Grain

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Chinese Journal of Structural Chemistry 2005年第12期24卷 1369-1374页

作者： ZHANG Wei-jia WANG tian-Min CUI Min School of Science Beijng University of Aeronutics and Astronautics Beijing 100083 China

Surface cell Madelung constant is firstly defined in calculating surface free energy of nanosized crystal grains, which explains the physical performance of small crystals and may be great benefit to make surface analysis and study dynamics of crystal nucleus growth. A new approximative expression of surface energy and relevant thermodynamic data was used in this calculation. A new formula and computing method for calculating the Madelung constant a of any complex crystals is proposed, and surface free energies and surface electrostatic energies of nanosized crystal grains as well as Madelung constant of some complex crystals are theoretically calculated in this paper. The surface free energy of nanosized crystal grain TiO2 and surface electrostatic energy（absolute value） of nanosized crystal grain α-A12O3 are found to be the biggest among other crystal grains.

关键词： Madelung constant surface free energy nanosized crystal grain

Lax connections in TT-deformed integrable field theories

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Chinese Physics C 2021年第9期45卷 125-135页

作者： Bin Chen Jue Hou jia tian School of Physics Peking UniversityNo.5 Yiheyuan RdBeijing 100871China Center for High Energy Physics Peking UniversityNo.5 Yiheyuan RdBeijing 100871China Peng Huanwu Center for Fundamental Theory Hefei 230026China Kavli Institute for Theoretical Sciences(KITS) University of Chinese Academy of ScienceBeijing 100190China

In this work,we attempt to construct the Lax connections of TT-deformed integrable field theories in two different *** reasonable assumptions,we make an ansatz and find the Lax pairs in the TT-deformed affine Toda theories and the principal chiral model by solving the Lax equations *** method is straightforward,but it may be difficult to apply for general *** then make use of a dynamic coordinate transformation to read the Lax connection in the deformed theory from the undeformed *** find that once the inverse of the transformation is available,the Lax connection can be read *** show the construction explicitly for a few classes of scalar models and find consistency with those determined using the first method.

关键词： integrable field theory Latex connection TT deformation

Use of Muscle Feeding Arteries as Recipient Vessels for Soft Tissue Reconstruction in Lower Extremities

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Current Medical Science 2020年第4期40卷 739-744页

作者： jia tian Zhen-bing CHEN Jin LI Department of Hand Surgery Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China

Summary:Microsurgical free tissue transfer is still playing an important role in lower extremity *** a suitable recipient artery for anastomosis is critical in the microsurgical procedure,especially in an extensive wound,or in a complex trauma combined with vascular *** April 2014 to March 2018,we retrospectively reviewed patients with traumatic/posttraumatic,oncologic,and electrical wounds in the lower *** treated with muscle feeding artery as recipient vessels were *** latissimus dorsi(LD)muscle free flap,anterior lateral thigh(ALT)perforator free flap,and deep inferior epigastric perforator(DIEP)free flap were *** muscle feeding arteries to vastus lateral muscle and to medial head of gastrocnemius muscle,concomitant veins,and great saphenous vein were used as recipient *** included in the study were caused by tumour in 2 cases,car accident in 3 cases,crushing in 3 cases,burns in one case,and electrical injury in one *** wound size varied from 14 cm x 6 cm to 30 cm x 20 ***,ALT,and DIEP free flaps were used in 6,3,and 4 patients,*** muscle feeding arteries to medial head of gastrocnemius muscle,to sartorius muscle,and to vastus lateral muscle were used as recipient arteries in 4,5,and one patient,*** and great saphenous veins were used as recipient veins in 10 and 4 patients,*** the muscle feeding artery is feasible to avoid injury to the main artery and facilitate dissection and anastomoses,particularly when the wound is located proximal to the mid-third of the lower leg.

关键词： muscle feeding artery recipient vessel end-to-end anastomosis end-to-side anastomosis

Double-ejection micro-cathode arc thruster applied to micro-satellite

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High Voltage 2023年第1期8卷 102-110页

作者： jia tian Wenzheng Liu Anton Nikiforov Nathalie De Geyter Rino Morent School of Electrical Engineering Beijing Jiaotong UniversityBeijingChina Research Unit Plasma Technology(RUPT) Department of Applied PhysicsGhent UniversityGhentBelgium

An innovative double-ejection micro-cathode arc thruster(AC_(d-μ)CAT),which consists of a cylindrical inner anode,a cylindrical outer cathode and two insulating sleeves(an inner insulating sleeve and an outer insulating sleeve),was *** differences in electrical characteristics,plasma parameters and propulsion performance between the newly proposed AC_(d-μ)CAT and a traditionalμCAT were *** results showed that compared to the traditionalμCAT structure,by using the AC_(d-μ)CAT,the peak value of produced thrust was increased 9.3 times,while the amplitude of the ion current and the ion-to-arc ratio were increased 5.4 and 5.9 times(from 1.2%to 7.1%),*** addition,data from Langmuir probe experiments indicated that peak values of the directional propagation speed and density of plasma plume were increased 3.1 times and 4.2 times,***,plasma plume directional ejection performance was also significantly *** study result will provide support for the development of a new-generationμCAT.

关键词： cylindrical inner outer

Preparation and electrocatalytic property of Au-Pt/SnO_2/GC composite electrode

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Rare Metals 2009年第4期28卷 350-354页

作者： YU Zhihui XIE jia BAI Jie tian Mi XIA Dingguo College of Environmental and Energy Engineering Beijing University of Technology Beijing 100124 China

Au-Pt/SnO2/GC composite electrode was prepared by self-assembling Au-Pt nanoparticles on SnO2 film, which was deposited on actived glassy carbon （GC）. Atomic force microscopy （AFM） and scanning electron microscopy （SEM） images revealed that dense and uniform Au-Pt particles with 25-nm diameter were dispersed on SnO2 film. X-ray photoelectron spectroscopy （XPS） results proved that there was an interaction between Au-Pt nanoparticles and SnO2 support. Electrochemical experiments showed that Au-Pt/SnOz/GC composite electrode had a good electrocatalytic activity to the oxidation of methanol

关键词： . electrochemistry composite electrode self-assembling Au-Pt SnO2 methanol oxidation