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The aggregation behavior of hydrogen (H) isotopes after low-energy plasma irradiation is particularly important for tungsten (W) in future fusion devices. Here, using the first-principles calculation, we demonstrated an interesting strain effect that may drive the planar aggregation of interstitial H atoms in W. Although there are attractive interactions between H atoms, the spontaneous nucleation of these platelet-like H clusters in strain-free W appears impossible even at high H concentrations (up to 0.1 at.%) because of the extremely low configurational entropy. However, applied uniaxial strain significantly increased the binding energy of H platelets and enabled planar H clusters to form. These results suggest that uniaxial strain enhances the nucleation and growth of H platelets in W, regardless of whether it is a compressive or tensile strain. Moreover, the binding energy of one-layer H clusters was lower than that of parallel H platelets, implying that the formation of multi-layer H clusters in W and their stability is also promoted by uniaxial strain. Meanwhile, the presence of planar H clusters dramatically reduced the vacancy formation energy in W, which in turn provided an extra trapping site to accommodate excessive H atoms. These results provide an important reference for understanding the H evolution in W-PFMs.

To analyze the development of coronavirus disease 2019(COVID-19), this study systematically retrieved relevant Chinese and English literatures from both CNKI and Web of Science database platforms by bibliometric research method and CiteSpace 5.5.R2 software to obtain information and visualize relevant literatures. A total of 695 Chinese and 446 English literatures were included in this paper. Statistics showed that China had published most of the literatures and established close cooperation with the United States and the United Kingdom. Through the analysis, Tongji Medical College of Huazhong University of Science and Technology and its affiliated hospitals published the largest number of the publications. Moreover, the highly productive journals including Journal of Traditional Chinese Medicine and The Lancet covered eight major fields, such as medicine, medical virology, radiation medicine, infectious disease, and traditional Chinese medicine. Besides, a total of 35 special COVID-19 funds were recently established to subsidize these studies. The key words and themes analysis indicated that protein structure of COVID-19, receptor targets and mechanisms of action, integration of traditional Chinese and Western medicine, screening and development of antiviral drugs from traditional Chinese medicine and Western medicine, vaccine research as well as epidemiological characteristics and prediction are current study hotspots. This study provides a reference for researchers to rapidly master main study directions of COVID-19 and screen out relevant literatures.