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46 results on '"Wen, Jian-Feng"'

1. Node-line Dirac semimetal manipulated by Kondo mechanism in nonsymmorphic CePt$_2$Si$_2$

Author

Ma, Hao-Tian, Ming, Xing, Zheng, Xiao-Jun, Wen, Jian-Feng, Wang, Yue-Chao, Liu, Yu, and Li, Huan

Subjects
Condensed Matter - Strongly Correlated Electrons
Abstract

Dirac node lines (DNLs) are characterized by Dirac-type linear crossings between valence and conduction bands along one-dimensional node lines in the Brillouin zone (BZ). Spin-orbit coupling (SOC) usually shifts the degeneracy at the crossings thus destroys DNLs, and so far the reported DNLs in a few materials are non-interacting type, making the search for robust interacting DNLs in real materials appealing. Here, via first-principle calculations, we reveal that Kondo interaction together with nonsymmorphic lattice symmetries can drive a robust interacting DNLs in a Kondo semimetal CePt_2Si_2, and the feature of DNLs can be significantly manipulated by Kondo behavior in different temperature regions. Based on the density function theory combining dynamical mean-field theory (DFT+DMFT), we predict a transition to Kondo-coherent state at coherent temperature T_coh= 80 K upon cooling, verified by temperature dependence of Ce-4f self-energy, Kondo resonance peak, magnetic susceptibility and momentum-resolved spectral. Below T_coh, well-resolved narrow heavy-fermion bands emerge near the Fermi level, constructing clearly visualized interacting DNLs locating at the BZ boundary, in which the Dirac fermions have strongly enhanced effective mass and reduced velocity. In contrast, above a crossover temperature T_KS =600 K, the destruction of local Kondo screening drives non-interacting DNLs which are comprised by light conduction electrons at the same location. These DNLs are protected by lattice nonsymmorphic symmetries thus robust under intrinsic strong SOC. Our proposal of DNLs which can be significantly manipulated according to Kondo behavior provides an unique realization of interacting Dirac semimetals in real strongly correlated materials, and serves as a convenient platform to investigate the effect of electronic correlations on topological materials., Comment: 9 pages, 9 figures

Published
2022
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24. Guest editorial of virtual special issue: Structural integrity in the context of carbon neutrality.

Author

Wen, Jian‐Feng and Tu, Shan‐Tung

Subjects
*CARBON offsetting, *FRACTURE mechanics, *MATERIAL fatigue, *HYDROGEN embrittlement of metals, *WELDED joints, *JET engines, *FATIGUE life
Abstract

This document is a guest editorial for a virtual special issue titled "Structural Integrity in the Context of Carbon Neutrality." The issue focuses on the importance of structural integrity in achieving carbon neutrality and features twelve papers that highlight breakthroughs in structural integrity research related to carbon neutrality. The papers cover topics such as suppressing hydrogen embrittlement, improving the reliability of conventional energy conversion systems, understanding fatigue failure mechanisms in gas turbine engines, investigating material properties and damage mechanisms, studying crack growth behavior, and enhancing the fatigue life of welded joints. The authors express their gratitude to the session chairs, reviewers, and authors for their contributions to the special issue. [Extracted from the article]

Published
2024
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29. High‐temperature creep‐fatigue‐oxidation behaviors of P92 steel: Evaluation of life prediction models.

Author

Wang, Kang‐Kang, Wen, Jian‐Feng, Xia, Xian‐Xi, Wang, Run‐Zi, Zhang, Guo‐Dong, Zhang, Xian‐Cheng, and Tu, Shan‐Tung

Subjects
*PREDICTION models, *DAMAGE models, *CYCLIC loads, *FATIGUE life, *LINEAR equations, *STEEL
Abstract

Damages caused by the effects of cyclic loading (fatigue) and high temperature (creep and oxidation) have been considered critical and need to be appropriately evaluated. A series of strain‐controlled fatigue and creep‐fatigue tests are performed on P92 at 873 K under oxygen‐containing environment. The creep‐fatigue life prediction results are summarized using models based on strain‐range partition, Manson–Coffin equation and linear damage summation (LDS) rule. Obviously, the models based on the LDS rule show relatively good performance with an error band of ±2.5. In view of the adverse effects of oxidation on creep‐fatigue endurance, this paper further develops a physically‐based oxidation damage equation, which is incorporated into LDS rule for the improvement of life assessment. The predicted and experimental results falling into ±1.5 error band proved the accuracy of the proposed oxidation damage equation in the LDS rule. Additionally, model selection criteria are recommended to evaluate the model prediction capabilities. Highlights: A series of fatigue, creep‐fatigue, and oxidation tests are performed on P92 at 873 K.Oxidation damage equation based on kinetics and concentration distribution is proposed.Error band is reduced from ±2.5 to ±1.5 by using the proposed oxidation damage equation.W‐SEDE‐O model performs best with the minimum error band & best statistical indicators. [ABSTRACT FROM AUTHOR]

Published
2023
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33. Heterojunction Structure ZnO/TiO2 Nanorods with Enhanced Photoelectrochemical Properties

Author

Hai Jin Li, Wen Jian Feng, Liangyou Lin, Ying Peng Gong, and Bo Chi

Subjects
Materials science, Nanostructure, Absorption spectroscopy, 020502 materials, Mechanical Engineering, Nanotechnology, Heterojunction, 02 engineering and technology, Tin oxide, Hydrothermal circulation, 0205 materials engineering, Chemical engineering, Mechanics of Materials, Rutile, General Materials Science, Nanorod, Wurtzite crystal structure
Abstract

This paper describes a simple two-step hydrothermal method for the design of heterojunction structure combined with TiO2 nanorods coated with ZnO nanoparticles. TiO2 nanorods on F-doped tin oxide (FTO) conducting glass are synthesized by hydrothermal method and ZnO coating is prepared through a two-step procedure. The XRD patterns confirm that the nanostructure consists of rutile TiO2 and wurtzite ZnO without any other impure phase. The FE-SEM results show that ZnO is uniformly distributing on the surface of TiO2 nanorods, forming a well-connecting heterojunction. PL studies and UV-vis absorption spectra present the enhanced optical performance of ZnO/TiO2 heterojunction. The heterojunction structure ZnO/TiO2 nanorods show excellent photoelectrochemical performance. The performance and the preparation parameters are also optimized accordingly.

Published
2017
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34. Effects of Stress Level and Stress State on Creep Ductility: Evaluation of Different Models

Author

Tu Shan-Tung, Zhang Xue-Wei, Gao Xin-Lin, Wen Jian-Feng, and Xuan Fuzhen

Subjects
Coalescence (physics), Materials science, Polymers and Plastics, business.industry, Mechanical Engineering, Metals and Alloys, 02 engineering and technology, Structural engineering, Strain rate, 021001 nanoscience & nanotechnology, Microstructure, Ductility factor, Stress level, 020303 mechanical engineering & transports, 0203 mechanical engineering, Creep, Operating temperature, Mechanics of Materials, Materials Chemistry, Ceramics and Composites, 0210 nano-technology, business, Test data
Abstract

The last few decades have witnessed an increasing emphasis on the development of strain-based approach for predicting the creep life or damage of components operating at elevated temperatures. Creep ductility, as a key parameter in this approach, may vary with a number of factors including strain rate, state of stress, operating temperature, material microstructure, etc. The present paper, however, is focused on reviewing the state-of-the-art understanding of the effects of stress level and stress state on the creep ductility. Mechanisms involving the void growth and coalescence are presented to describe the role of stress level in the variation of uniaxial creep ductility. The prediction capacity of existing empirical ductility models is also assessed in light of uniaxial test data. On the other hand, a vast body of multiaxial creep test data, collected from open literature, is utilized to examine the influence of the state of stress on the creep ductility. Then, a variety of multiaxial ductility factor models are introduced and evaluated with the available experimental data. Finally, a brief discussion on the dependence of creep ductility on the stress triaxiality and Lode parameter, predicted by numerical methods, is provided.

Published
2016
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46. To flip or not to flip? Assessing the inversion barrier of the tetraphenylene framework with enantiopure 2,15-dideuteriotetraphenylene and 2,7-dimethyltetraphenylene.

Author

Huang H, Stewart T, Gutmann M, Ohhara T, Niimura N, Li YX, Wen JF, Bau R, and Wong HN

Subjects
Computer Simulation, Models, Chemical, Molecular Structure, Neutron Diffraction, Stereoisomerism, Terphenyl Compounds chemical synthesis, Time Factors, Terphenyl Compounds chemistry
Abstract

Two chiral tetraphenylenes, 2,15-dideuteriotetraphenylene (7) and 2,7-dimethyltetraphenylene (15) were synthesized and resolved to address the tetraphenylene inversion barrier problem. Neutron diffraction investigation of enantiopure 7 showed that the molecule retained its chirality integrity during its synthesis from enantiopure precursors and therefore rules out the possibility of the tetraphenylene framework possessing a low-energy barrier to inversion. Thermal study on 15 and tetraphenylene 1 further revealed that their inversion barriers were not overcome up to 600 degrees C, at which temperature these compounds underwent skeletal contraction into triphenylene with activation energies of 62.8 and 58.2 kcal/mol, respectively. This result is supported by computational studies which yielded an inversion barrier of 135 kcal/mol for tetraphenylene as a consequence of the peri-hydrogen repulsions at its planar conformation.

Published
2009
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