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Terahertz (THz) communications are promising to be the next frontier for wireless network but suffer from severe attenuation and poor diffraction. To address these challenges, this paper integrates two state-of-the-art technology, i.e., massive multiple input multiple output (MIMO) and reconfigurable intelligent surfaces (RISs), into THz communication to stablish effective and stable connection. Owing to the passivity of the RISs, channel estimation remains an open problem, besides, traditional fully-digital beamforming (FDB) can not be applied in massive MIMO due to its high hardware cost. In sight of this, this paper develops a cooperative channel estimation procedure for RIS-assisted MIMO system via beam training that exploits the advantages of massive MIMO and poor scattering nature of THz channel. The whole procedure is developed based on cost-efficient hybrid beamforming (HB) architectures. Moreover, this paper designs two different codebooks for efficiently realizing the proposed estimation procedure via 3-tree hierarchical search. The two codebooks are referred to as tree dictionary (TD) codebook and phase shifter deactivation (PSD) codebook, with different advantages catering for various scenarios. Using the estimation information, this paper develops two closed-form transmission designs, i.e., direct allocation (DA) design and zero-forcing allocation (ZFA) design, for maximizing the overall spectral efficiency.

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The article aims to study the coupling coordination and spatial correlation effects of green finance (GF) and high-quality economic development (HQED) in 30 Chinese provinces. The index system of GF and HQED is constructed by selecting relevant index data from 2007 to 2017. The index of GF and HQED is measured by the entropy value method. Next, the coupling coordination degree (CCD) and spatial association strength are calculated based on the index using the coupling coordination degree model and the gravity model. Then the driving factors of the CCD between GF and HQED are analyzed by using geographic detectors. Finally, the spatial association network is constructed and its robustness is studied. The research results show that the coupling coordination degree between GF and HQED in each province is generally low, with strong regional heterogeneity, and the coupling coordination degree shows a trend of decay from the eastern region to the western region, but the western region has more room for development. Green credit, green, coordination, and sharing are the strong driving factors of the CCD between GF and HQED. The network of spatial association between GF and HQED in each province is gradually tightened, making the western peripheral provinces more closely connected with the eastern provinces through the intermediate node provinces. The network robustness of GF and HQED is more influenced by provinces with higher node degree values. Accordingly, the article proposes that China should continuously improve relevant GF policies, environmental disclosure systems, enhance green innovation technology and guide private capital to enter the GF market.