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Your search keyword '"Guo, Xiangwei"' showing total 135 results
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135 results on '"Guo, Xiangwei"'

1. Theory of nonlinear terahertz susceptibility in ferroelectrics

Author

Zhu, Yujie, Chen, Taorui, Ross, Aiden, Wang, Bo, Guo, Xiangwei, Gopalan, Venkatraman, Chen, Long-Qing, and Hu, Jia-Mian

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

An analytical theory is developed for predicting the nonlinear susceptibility of ionic polarization to continuous electromagnetic waves in both bulk and strained thin film ferroelectrics. Using a perturbation method for solving the nonlinear equation of motion for ionic polarization within the framework of Landau-Ginzburg-Devonshire theory, the full second-order nonlinear susceptibility tensor is derived as a function of frequency, temperature, and strain. The theory predicts the coexistence of a significantly enhanced second-order dielectric susceptibility and a relatively low dielectric loss in BaTiO3 films with a strain-stabilized monoclinic ferroelectric phase and in a strained SrTiO3 film near its temperature-driven second-order ferroelectric-to-paraelectric phase transition. This work establishes a theoretical framework for predicting and exploiting nonlinear interactions between THz waves and ferroelectric materials, and more generally, suggests exciting opportunities to strain-engineer nonlinear dynamical properties of ferroelectrics beyond the static and quasi-static limits.

Published
2024

2. Non-volatile electric-field control of inversion symmetry

Author

Caretta, Lucas, Shao, Yu-Tsun, Yu, Jia, Mei, Antonio B, Grosso, Bastien F, Dai, Cheng, Behera, Piush, Lee, Daehun, McCarter, Margaret, Parsonnet, Eric, K. P, Harikrishnan, Xue, Fei, Guo, Xiangwei, Barnard, Edward S, Ganschow, Steffen, Hong, Zijian, Raja, Archana, Martin, Lane W, Chen, Long-Qing, Fiebig, Manfred, Lai, Keji, Spaldin, Nicola A, Muller, David A, Schlom, Darrell G, and Ramesh, Ramamoorthy

Subjects
Physical Sciences, Condensed Matter Physics, Nanoscience & Nanotechnology
Abstract

Competition between ground states at phase boundaries can lead to significant changes in properties under stimuli, particularly when these ground states have different crystal symmetries. A key challenge is to stabilize and control the coexistence of symmetry-distinct phases. Using BiFeO3 layers confined between layers of dielectric TbScO3 as a model system, we stabilize the mixed-phase coexistence of centrosymmetric and non-centrosymmetric BiFeO3 phases at room temperature with antipolar, insulating and polar semiconducting behaviour, respectively. Application of orthogonal in-plane electric (polar) fields results in reversible non-volatile interconversion between the two phases, hence removing and introducing centrosymmetry. Counterintuitively, we find that an electric field 'erases' polarization, resulting from the anisotropy in octahedral tilts introduced by the interweaving TbScO3 layers. Consequently, this interconversion between centrosymmetric and non-centrosymmetric phases generates changes in the non-linear optical response of over three orders of magnitude, resistivity of over five orders of magnitude and control of microscopic polar order. Our work establishes a platform for cross-functional devices that take advantage of changes in optical, electrical and ferroic responses, and demonstrates octahedral tilts as an important order parameter in materials interface design.

Published
2023

16. NaBH4 reduced Mn-doped cobalt tetroxide R-MnxCo3−xO4 catalysts with plentiful oxygen vacancies for HCHO oxidation at low temperature.

Author

Yan, Gang, Du, Xiaojun, Guo, Xiangwei, Cao, Xuzheng, and Shi, Hongfei

Subjects
OXYGEN reduction, COBALT catalysts, LOW temperatures, REACTIVE oxygen species, CATALYSTS, CATALYTIC oxidation, CATALYTIC activity
Abstract

Developing low-cost and efficient catalysts for the oxidation of formaldehyde (HCHO) is crucial for preservation of the environment. The main challenge of this study is how to develop an efficient, stable, and inexpensive catalyst that can oxidize HCHO at low temperatures. Herein, the reduced Mn-doped cobalt tetroxide R-MnxCo3−xO4 catalyst was prepared by simple co-precipitation and annealing treatment followed by reduction of NaBH4. The prepared R-MnxCo3−xO4 showed remarkable enhanced activity for HCHO oxidation at low temperature. The R-MnCo2O4 catalyst can oxidize and decompose 79% of HCHO at a low temperature of 50 °C and exhibits excellent catalytic stability. The improved catalytic activity can be attributed to the increase in oxygen vacancy concentration and the improvement in redox performance. The TGA test shows that the content of oxygen vacancies in the R-MnCo2O4 catalyst can reach 5.77% (atomic ratio). The H2-TPR, O2-TPD and O2-TPO tests indicated that the surface oxygen vacancies can promote oxygen mobility and facilitate the formation of reactive oxygen species during the formaldehyde catalytic oxidation process. This study reveals the importance of surface oxygen vacancies in improving the catalytic oxidation activity of catalysts, providing possibilities for the development of high-performance catalysts through atomic doping and reduction modification. [ABSTRACT FROM AUTHOR]

Published
2024
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19. Across the geo-political landscape : Chinese women intellectuals' political networks in the wartime era 1937-1949

Author

Guo, Xiangwei, Boermel, Anna, and Altehenger, Jennifer Elisabeth

Subjects
320.082
Abstract

Examining women intellectuals’ political networks across different political parties, organisations and institutions, my PhD thesis aims to provide an in-depth analysis of women intellectuals’ political engagement, communication and identification during the War of Resistance (1937-1945) and the following Civil War (1946-1949). Taking “network” as an approach to study modern Chinese history, this thesis aims to reveal and interpret the historical dynamics of war, politics and gender in the 1930s and 1940s China, at national, local and individual levels. Focusing on “women intellectuals” as both a social and political group active in the KMT-held major cities, this thesis places their networks in the spaces of knowledge and identity making, in the context of China’s war and crisis. I consider the process of their political engagement and identification as both a reflection and a component of the wartime geo-political landscape. I also argue that the War of Resistance enlarged the geographical, social, cultural and political spaces for women intellectuals’ political networking cross party lines and political boundaries. These spaces were never fixed, but changing according to the social, political and economic conditions, within which women intellectuals’ political identification with the KMT, the CCP, and the minor political parties were shaped and reshaped. Breaking through the “barrier” years of 1937, 1945 and 1949, this thesis aims to demonstrate both the consistencies and variations in women intellectuals’ political networking, not only during the War of Resistance, but also before and after the War. And avoiding a teleological view of the wartime women’s movement based on CCP narratives after 1949, I will not only analyse archival documents collected from non-CCP organisations but also explore the personal accounts of women intellectuals who held different political affiliations during the War. By revealing the complexity, diversity and flexibility of women intellectuals’ political networks, this thesis will deepen the current knowledge of the social and political transformations in wartime China.

Published
2015

25. Lithium-Ion Battery State of Health Estimation Method Based on Frequency-Domain-Assisted Data Decoupling and Time–Frequency Features Compensation Learning Network

Author

Zhao, Yunji, Guo, Hui, and Guo, Xiangwei

Abstract

Accurate state of health (SOH) estimation is critical for lithium-ion battery maintenance and safety. Currently, numerous time series models based on deep learning have been applied to online prediction of SOH. However, the strong nonlinear coupling between different sample data seriously interferes with the estimation accuracy of the existing models. Rational network expansion can alleviate the issue, but limited samples pose a significant challenge to model training. Therefore, how to effectively reduce the strong nonlinear coupling between data is the key to achieve high accuracy prediction of SOH. In view of this, this article proposes an SOH estimation method based on frequency-domain-assisted data decoupling and time-frequency features compensation learning network (FA2D-TFCLNet). Specifically, this article proposes a Mel filtering algorithm to achieve preliminary nonlinear decoupling of the discharge data. Subsequently, time-domain features and frequency-domain features are fed in parallel to TFCLNet, which consists of a parallel multiscale convolutional attention (CPMCA)-based local receptor and Transformer. By organically combining the refined local aging features mined by the CPMCA and the discriminative global semantic relations captured by the Transformer, the proposed TFCLNet effectively realizes the comprehensive perception and deep decoupling of discharge data, thereby obtaining competitive SOH estimation accuracy. To validate the effectiveness of the proposed method, relevant experiments are conducted on NASA PCoE and Oxford datasets, and the results prove that the method has a high accuracy in estimating battery SOH.

Published
2024
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29. Non-volatile electric-field control of inversion symmetry

Author

Caretta, Lucas, primary, Shao, Yu-Tsun, additional, Yu, Jia, additional, Mei, Antonio B., additional, Grosso, Bastien F., additional, Dai, Cheng, additional, Behera, Piush, additional, Lee, Daehun, additional, McCarter, Margaret, additional, Parsonnet, Eric, additional, K. P, Harikrishnan, additional, Xue, Fei, additional, Guo, Xiangwei, additional, Barnard, Edward S., additional, Ganschow, Steffen, additional, Hong, Zijian, additional, Raja, Archana, additional, Martin, Lane W., additional, Chen, Long-Qing, additional, Fiebig, Manfred, additional, Lai, Keji, additional, Spaldin, Nicola A., additional, Muller, David A., additional, Schlom, Darrell G., additional, and Ramesh, Ramamoorthy, additional

Published
2022
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39. Research on combination of passive magnetic bearing and mechanical bearing for vertical axis wind turbine

Author

Du Shaotong, Cao Di, Yang Ming, Guo Xiangwei, Zhu Jun, Liu Penghui, and Zhang Zhenyi

Subjects
010302 applied physics, Vertical axis wind turbine, 0209 industrial biotechnology, Materials science, Bearing (mechanical), business.industry, Mechanical Engineering, Magnetic bearing, 02 engineering and technology, Structural engineering, Condensed Matter Physics, 01 natural sciences, Electronic, Optical and Magnetic Materials, law.invention, 020901 industrial engineering & automation, Mechanics of Materials, law, 0103 physical sciences, Electrical and Electronic Engineering, business
Abstract

Aiming at the “light wind start, light wind power generation” of vertical axis wind turbine, a new T-shaped radial passive magnetic bearing with high suspension characteristics is proposed. Passive magnetic bearings used in vertical axis wind turbines usually have small bearing capacity and difficult magnetization. The new T-shaped radial PMB can improve the radial bearing capacity, and the three magnetic rings all adopt simple axial magnetization. The new T-shaped radial PMB is combined with mechanical auxiliary bearing to form the suspension system of wind turbine. In the stable state, the suspension system can realize radial and axial stable suspension. The structure and working principle of the suspension system are briefly described. Through the finite element simulation, the characteristics of the new T-shaped radial PMB, the traditional double-ring PMB and the T-shaped PMBs are compared. Taking the high bearing capacity and high stiffness of the new T-shaped radial PMB as the optimization objective, the multi-objective optimization of the new T-shaped radial PMB was carried out by changing its geometric parameters (inner diameter, magnetization length and air gap). The research results show that: Under the same bearing capacity, the volume of the new T-shaped radial PMB is reduced by about 78.64%. Under the same volume, its bearing capacity increased by about 30.7%, and its stiffness increased by about 96.1%. After optimization, its radial bearing capacity increased to 101.38 N, and its stiffness increased to 202.76 N/mm.

Published
2021

41. Active balancing method for series battery pack based on flyback converter

Author

Longyun Kang, Guo Xiangwei, Liu Zhen, Geng Jiahao, and Xu Xiaozhuo

Subjects
010302 applied physics, Battery (electricity), Flyback converter, Computer science, 020208 electrical & electronic engineering, Topology (electrical circuits), 02 engineering and technology, Internal resistance, 01 natural sciences, Battery pack, Automotive engineering, Power (physics), Control and Systems Engineering, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Electrical and Electronic Engineering, Primary cell, Energy (signal processing)
Abstract

Lithium battery has become the main power source of new energy vehicles due to its high energy density and low self-discharge rate. In the actual use of the series battery pack, due to the internal resistance and self-discharge rate of batteries and other factors, inconsistencies between the individual cells are unavoidable. Such inconsistencies will reduce the energy utilisation rate and service life of the battery pack, and even endanger the safety of the battery systems. To improve the consistency of the series battery pack, a novel balancing method based on the flyback converter is proposed in this study. The flyback converter with a simple and reliable structure is used to realise the energy transfer between the whole battery pack and any single cell. Compared with the traditional balancing topology, the topology proposed in this study reduces the number of components and the volume of the balancing system, and only needs one set of control signals on the converter primary side, thus reducing the control difficulty. The experimental results show the effectiveness of the novel balancing method.

Published
2020

43. Synergistic effects of bithiophene ammonium salt for high-performance perovskite solar cells

Author

Xu, Chang, primary, Zuo, Lijian, additional, Hang, Pengjie, additional, Guo, Xiangwei, additional, Pan, Youwen, additional, Zhou, Guanqing, additional, Chen, Tianyi, additional, Niu, Benfang, additional, Xu, Xingqi, additional, Hong, Zijian, additional, Wang, Dawei, additional, Zhu, Haiming, additional, Yu, Xuegong, additional, Yang, Deren, additional, and Chen, Hongzheng, additional

Published
2022
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46. A Flyback Converter-based Hybrid Balancing Method for Series-Connected Battery Pack in Electric Vehicles

Author

Liu Zhen, Geng Jiahao, Wenping Cao, Xiaozhuo Xu, and Guo Xiangwei

Subjects
Battery (electricity), Computer Networks and Communications, Computer science, Buck converter, Flyback converter, Flyback transformer, Aerospace Engineering, Topology (electrical circuits), Battery pack, Energy storage, Automotive engineering, Automotive Engineering, Electrical and Electronic Engineering, Voltage
Abstract

An active balancing method based on two flyback converters is proposed for series-connected battery pack. Balanced energy can be transferred between the whole battery and any single cell. The proposed topology reduces the number of energy storage components, the volume and the cost of the balancing system. And it has the characteristics of fast balancing speed and high balancing efficiency. Based on the topology, a dual-objective hybrid control strategy is proposed, which can reduce the highest voltage and boost the lowest voltage in the charging or discharging process of the cells in one sampling period, so as to improve the balancing speed. Simulation and experimental results show that the proposed method has a good balancing effect and can significantly improve the consistency of series battery pack. This work is potentially significant in terms of improved reliability of battery packs and savings of costs and lives in safety-critical applications.

Published
2021

49. A Flyback Converter-based Hybrid Balancing Method for Series-Connected Battery Pack in Electric Vehicles

Author

Guo, Xiangwei, Geng, Jiahao, Liu, Zhen, Xu, Xiaozhuo, Cao, Wenping, Guo, Xiangwei, Geng, Jiahao, Liu, Zhen, Xu, Xiaozhuo, and Cao, Wenping

Abstract

An active balancing method based on two flyback converters is proposed for series-connected battery pack. Balanced energy can be transferred between the whole battery and any single cell. The proposed topology reduces the number of energy storage components, the volume and the cost of the balancing system. And it has the characteristics of fast balancing speed and high balancing efficiency. Based on the topology, a dual-objective hybrid control strategy is proposed, which can reduce the highest voltage and boost the lowest voltage in the charging or discharging process of the cells simultaneously, so as to improve the balancing speed. Simulation and experimental results show that the proposed method has a good balancing effect and can significantly improve the consistency of series battery pack. This work is potentially significant in terms of improved reliability of battery packs and savings of costs and lives in safety-critical applications.

Published
2021

50. Floating Particles in the Melt during the Growth of β -Ga 2 O 3 Single Crystals Using the Czochralski Method.

Author

Liu, Yingying, Guo, Xiangwei, Xia, Ning, Hong, Zijian, Zhang, Hui, and Yang, Deren

Subjects
SINGLE crystals, PROTECTIVE coatings, DENSITY functional theory, INTERFACE structures
Abstract

Floating particles often appear during the Czochralski (CZ) growth of β-Ga2O3 in the Ir crucible, thereby impeding the seeding process. Identifying the floating nanoparticles and then inhibiting or removing them is critical for growing high-quality β-Ga2O3 single crystals. We grew β-Ga2O3 crystals containing floating particles using the CZ method. It is indicated that the floating particles were composed of Ir with a face-centered cubic (fcc) structure. In addition, the β-Ga2O3/Ir interface was comprehensively characterized, showing sharp and straight configuration on the whole with small fluctuations at the nanoscale. Combined with density functional theory (DFT) calculation, we found that Ir-O bonding was responsible for stabilizing the interface. Accordingly, the atomic configuration of the interface with the stablest structure, including the relaxed one, was determined. Based on the formation mechanism of the floating particles, we propose three effective strategies, including blowing sufficient oxygen into the bottom of the Ir crucible, coating a protective layer on its inwall and equipping a mechanical arm for inhibiting or removing them. [ABSTRACT FROM AUTHOR]

Published
2022
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