Browsing by Author "Liang, Jing"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Adaptive Sector Splitting based on Channel Charting in Massive MIMO Cellular Systems
    (2021-06-15) Al-Tous, Hanan; Tirkkonen, Olav; Liang, Jing; Department of Communications and Networking; Communications Theory; Huawei Technologies Co., Ltd.
    We consider a downlink scenario where a multiantenna base station in a sectorized cellular system creates multiple logical cells in each sector, applying Adaptive Sector Splitting (ASS). In ASS, a population of User Equipments (UEs) is grouped based on radio Channel State Information (CSI), groups are assigned to cells, and the virtual antennas serving the cells are optimized based on CSI. Grouping UEs based on covariance matrix similarity may result in considerable spatial overlap of the UE groups, and a need for frequent handovers for mobile UEs. To reduce handovers, an improved grouping strategy that takes into account UE physical locations is needed. We use Channel Charting (CC) to learn the radio map of the cell from uplink CSI, and consider UE grouping based on CC locations aiming to maximize the mean distance of UEs to virtual cell borders without the need to know the physical locations of the UEs. Simulation results show that ASS groups based on CC are more compact than angle-of-arrival and covariance matrix based groupings from the literature.
  • Thumbnail Image
    Item
    Extent of global decarbonization of the power sector through energy policies and governance capacity
    (Springer, 2024-12) Peng, Xu; Sun, Laixiang; Feng, Kuishuang; Zhong, Honglin; Liang, Jing; Zhang, Chao; Zhao, Dandan; Chen, Hong; Long, Ruyin; Xing, Zhencheng; Hubacek, Klaus; Department of Built Environment; Water and Environmental Eng.; Jiangnan University; University of Maryland, College Park; Shandong University; Harbin Institute of Technology; Tongji University; Nanjing University; University of Groningen
    During the 2007-2008 global financial crisis, many countries enacted clean energy policies as a part of their economic stimulus packages. These policies are believed to have contributed to a significant reduction in the CO2 intensity of electricity. Here we conduct a retrospective overview and evaluation of energy policies’ effectiveness in reducing the CO2 intensity of electricity. We utilize governance capacity as a measure of policy implementation stringency, and the interaction between governance capacity and the number of categorized policies to adjust policy variables for governance effectiveness. We distinguish between the short- and long-term effects of these policies to investigate the impacts of policy instruments on CO2 mitigation. The results suggest that the increased policy efforts, when executed with effective governance, have led to long-term cumulative effects. Our findings provide insights into the spatiotemporal dynamics of energy policies in CO2 mitigation, serving as a reference for policymakers in the post-COVID-19 era.
  • Thumbnail Image
    Item
    Giant valley coherence at room temperature in 3R WS2 with broken inversion symmetry
    (AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE, 2019-01-01) Du, Luojun; Tang, Jian; Liang, Jing; Liao, Mengzhou; Jia, Zhiyan; Zhang, Qinghua; Zhao, Yanchong; Yang, Rong; Shi, Dongxia; Gu, Lin; Xiang, Jianyong; Liu, Kaihui; Sun, Zhipei; Zhang, Guangyu; Department of Electronics and Nanoengineering; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Chinese Academy of Sciences; Peking University; Yanshan University
    Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties. In 3R-stacked transition metal dichalcogenides, the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum, providing an unprecedented platform for valleytronics. Here, we study the valley coherence of 3R WS2 large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature. Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence. The valley coherence of direct A (B) excitons can reach 0.742 (0.653) with excitation conditions on resonance with it. Such giant and thickness-independent valley coherence of large single-crystal 3R WS2 at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.
  • No Thumbnail Available
    Item
    Optical fibres with embedded two-dimensional materials for ultrahigh nonlinearity
    (Nature Publishing Group, 2020-12) Zuo, Yonggang; Yu, Wentao; Liu, Can; Cheng, Xu; Qiao, Ruixi; Liang, Jing; Zhou, Xu; Wang, Jinhuan; Wu, Muhong; Zhao, Yun; Gao, Peng; Wu, Shiwei; Sun, Zhipei; Liu, Kaihui; Bai, Xuedong; Liu, Zhongfan; Department of Electronics and Nanoengineering; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Chinese Academy of Sciences; Peking University; Beijing Institute of Technology; Fudan University
    Nonlinear optical fibres have been employed for a vast number of applications, including optical frequency conversion, ultrafast laser and optical communication1–4. In current manufacturing technologies, nonlinearity is realized by the injection of nonlinear materials into fibres5–7 or the fabrication of microstructured fibres8–10. Both strategies, however, suffer from either low optical nonlinearity or poor design flexibility. Here, we report the direct growth of MoS2, a highly nonlinear two-dimensional material11, onto the internal walls of a SiO2 optical fibre. This growth is realized via a two-step chemical vapour deposition method, where a solid precursor is pre-deposited to guarantee a homogeneous feedstock before achieving uniform two-dimensional material growth along the entire fibre walls. By using the as-fabricated 25-cm-long fibre, both second- and third-harmonic generation could be enhanced by ~300 times compared with monolayer MoS2/silica. Propagation losses remain at ~0.1 dB cm–1 for a wide frequency range. In addition, we demonstrate an all-fibre mode-locked laser (~6 mW output, ~500 fs pulse width and ~41 MHz repetition rate) by integrating the two-dimensional-material-embedded optical fibre as a saturable absorber. Initial tests show that our fabrication strategy is amenable to other transition metal dichalcogenides, making these embedded fibres versatile for several all-fibre nonlinear optics and optoelectronics applications.
  • Thumbnail Image
    Item
    Robust circular polarization of indirect Q-K transitions in bilayer 3R-W S2
    (American Physical Society, 2019-10-23) Du, Luojun; Zhang, Qian; Zhang, Tingting; Jia, Zhiyan; Liang, Jing; Liu, Gui Bin; Yang, Rong; Shi, Dongxia; Xiang, Jianyong; Liu, Kaihui; Sun, Zhipei; Yao, Yugui; Zhang, Qingming; Zhang, Guangyu; Department of Electronics and Nanoengineering; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Renmin University of China; Chinese Academy of Sciences; Yanshan University; Peking University; Beijing Institute of Technology
    Valley-contrasting Berry curvature and orbital magnetic moment have led to highly selective circular polarization of direct excitons at the K valleys in transition-metal dichalcogenides. In addition to K valleys, Q valleys, another critical point in the conduction band, also possess well-defined but distinct magnetic moment. Being akin to the direct excitons at K valleys, indirect excitons associated with Q (K) valleys in the conduction (valence) band could allow circular polarization in principle. Here, we report an experimental observation of the circular polarization of indirect Q-K transitions in noncentrosymmetric bilayer 3R-WS2. In stark contrast to the circular polarization of direct excitons which depolarizes with increasing lattice temperature, the circular polarization of indirect Q-K excitons is extremely robust and independent on the temperature. Such robust circular polarization can be understood as follows: The spin-orbit coupling in the Q valley is much stronger than that in the K point of the conduction band, significantly suppressing the temperature induced valley depolarization. Our results open up opportunities for exotic valleytronics and quantum information processing applications.