China's advance to the forefront of scientific research is one of the 21st century's most surprising developments, with implications for a world where knowledge is arguably “the one ring that rules them all.” This paper provides new estimates of China's contribution to global science that far exceed estimates based on the proportion of papers with Chinese addresses in databases of international journals. Address‐based measures ignore articles written by Chinese researchers with non‐Chinese addresses and articles in Chinese language journals not indexed in those databases. Taking account of these contributions, we attribute 36 percent of 2016 global scientific articles to China. Taking account of increased citations to Chinese‐addressed articles relative to the global average as well, we attribute 37 percent of global citations to scientific articles published in 2013 to China. With shares of articles and citations more than twice its share of global population or GDP, China has achieved a comparative advantage in knowledge that has implications for the division of labor and trade among countries and for the direction of research and of technological and economic development worldwide.
Zero-group-velocity (ZGV) waves have the peculiarity of being stationary, and thus locally confining energy. Although they are particularly useful in evaluation applications, they have not yet been tracked in two dimensions. Here we image gigahertz zero-group-velocity Lamb waves in the time domain by means of an ultrafast optical technique, revealing their stationary nature and their acoustic energy localization. The acoustic field is imaged to micron resolution on a nanoscale bilayer consisting of a silicon-nitride plate coated with a titanium film. Temporal and spatiotemporal Fourier transforms combined with a technique involving the intensity modulation of the optical pump and probe beams gives access to arbitrary acoustic frequencies, allowing ZGV modes to be isolated. The dispersion curves of the bilayer system are extracted together with the quality factor Q and lifetime of the first ZGV mode. Applications include the testing of bonded nanostructures.
Featured Application: This study provides a non-contact method of defect detection and localization in underwater plates using pure S 0 mode of Lamb wave with small dispersion generated by laterally distributed laser source.Abstract: When working in humid environments, corrosion defects are easily produced in metallic plates. For defect detection in underwater plates, symmetric modes of Lamb waves are widely used because of their characteristics including long propagating distance and high sensitivity to defects. In this study, we extend our previous work by applying the laser laterally generated S 0 mode to detection and localization of defects represented by artificial notches in an aluminum plate immersed in water. Pure non-dispersive S 0 mode is generated in an underwater plate by lateral laser source irradiation and its fd (frequency·thickness) range is selected by theoretical calculation. Using this lateral excitation, the S 0 mode is enhanced; meanwhile, the A 0 mode is effectively suppressed. The mode-converted A 0 mode from the incident S 0 mode is used to detect and localize the defect. The results reveal a significantly improved capability to detect defects in an underwater plate using the laser laterally generated S 0 mode, while that using A 0 is limited due to its high attenuation. Furthermore, owing to the long propagating distance and the non-dispersion characteristics of the S 0 generated by the lateral laser source, multiple defects can also be detected and localized according to the mode conversion at the defects.
From 2000 to 2016 China increased its scientific publications in the international journals indexed by Scopus to become the largest contributor to global science, accounting for about 23% of journal articles adjusted for the Chinese share of addresses or names on publications. Publications with all-China addresses contributed the most to the increase, followed by crosscountry collaborations and papers by Chinese-named researchers outside the country. The same period also saw a huge increase in scientific publications in Chinese language journals not indexed in Scopus. We estimate that while Chinese language papers gain about 1/5th as many citations as non-Chinese (largely English) papers in Scopus they are so numerous that even valued as making 1/5th the contribution of a Scopus paper, China accounts for 36% of global scientific papers defined as Scopus papers and China language equivalent papers and for 37% of citations to those papers. China's move to the forefront of scientific inquiry makes it a key driver of the direction of scientific and technological progress and of the knowledge-based economies of the foreseeable future.
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