This paper investigates the impact of China's city size and urban population concentration on city productivity by developing a distinctive index based on global nighttime light data. Using the panel data of 280 prefecture cities from 2004 to 2013 and employing dynamic system generalized method of moments and panel threshold model regression techniques, our results show that city size has a positive impact on city productivity; therefore, cities in China still have the potential to expand. While moderate urban population concentration can benefit city productivity, excessively concentrated urban population distribution may impede the growth of city productivity. We also find that the level of labor income significantly affects the impacts of urban agglomeration on labor productivity. Therefore, our results imply that city development policies should focus more on how to appropriately allocate economic activities and adjust population distribution in urban areas according to different stages of economic development.
City clusters are important carriers for China’s future urbanization and vital areas for promoting coordinated regional development and common prosperity. The authors first divide the city clusters into Types I, II, and III according to the characteristics of their development stages, and measure the degree of development of city clusters by using city-level night time light (NTL) data and inter-city commuting time, and empirically identify the types of China’s city clusters. On that basis, the authors examine the influence of city cluster development on the inter-city disparity from a perspective of urban agglomeration. The results show that the development of Type I city clusters can lead to the widest inter-city disparity, and that of Type II city clusters ranks the second place in this regard, while that of Type III city clusters can narrow the inter-city disparity. Furthermore, using the 268-year historical geographic data of the Qing Dynasty, the authors construct instrumental variables to address the endogeneity issues, and find that the above conclusions are robust. This study also finds that the factor allocation for the development of Types I and II city clusters is oriented towards labor, while that for Type III city clusters is oriented towards capital. Besides, different types of city clusters vary in the extent of correcting factor misallocation for their development. The differences in the orientation of factor allocation and the extent of factor misallocation correction constitute the main mechanism for the heterogeneous influence of city cluster development on the inter-city disparity. China’s city cluster development strategy should adopt a category-based approach to avoid homogenization, conform to the objective laws, and make greater use of central cities’ spatial spillover effects.
Plasmonic lithography can utilize evanescent waves to produce subdiffraction patterns. However, the high loss and shallow depth of patterns severely obstruct its application in practice. In this work, a large focal depth is achieved for deep subwavelength lithography. It is accomplished by employing radially polarized light to excite surface plasmons on a concentric annular grating and combining designed epsilon-near-zero metamaterial to select a high spatial frequency mode, which can shape an evanescent Bessel beam in a photoresist (PR). Moreover, the intensity distribution of the subdiffraction beam can be further enhanced and uniformized by adding reflective layers. It is shown that a needle-like beam with a focal depth of over 500 nm (
1.23
λ
) is formed in the PR layer, and the full width at half maximum of the beam is widened from only 80 nm (
0.2
λ
) to 94 nm (
0.23
λ
). The analyses indicate that this design is applicable for direct writing lithography to produce super-resolution patterns with small feature size, high aspect ratio, and strong field intensity.
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