Microporous starch was prepared from corn starch by glucoamylase catalysis combined with ultrasonic treatment. Twenty milliliters of starch slurries (40, 60, and 80% w/w) were treated with 0.05% v/v glucoamylase (enzyme activity >100 000 U/g), or a combination of 0.05% v/v glucoamylase with ultrasound at 100 W (20% power), 200 W (40% power), and 300 W (60% power) for 10, 30, and 50 min concurrently or sequentially. Degree of hydrolysis and degree of oil absorption were applied as indexes to evaluate the quality of the microporous starch. The microstructures, crystalline structures, and pasting properties of microporous starch were studied by SEM, XRD, and rapid visco analyzer (RVA), respectively. The results indicated that the preferred combination was sonication at 200 W (40% power) for 50 min during glucoamylase digestion with 40% slurry concentration. The results of this study provide an efficient method for microporous starch production.

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The use of Lamb waves for structural health monitoring (SHM) has complicated by its multi-mode character and dispersion effect, which impacts the damage positioning and high-resolution imaging. The group velocity dispersion curves of Lamb waves can be employed to warp the frequency axis, and then to establish warped frequency transform (WFT) to process Lamb waves. In this paper, received signals are directly compensated with warped frequency transform to suppress dispersion, and a new imaging method is proposed based on warped frequency transform. The propagation of Lamb waves in damaged aluminum plate is simulated by finite element software ABAQUS, results show that warped frequency transform can effectively compensate dispersive wave-packets, and high-resolution damage imaging can be obtained by the proposed method.

Debate on the shift from a monocentric to polycentric urban structure has been extensive. Polycentricity generally refers to the co-existence of several centers in a city. Existing studies regarding China have mainly focused on the morphological characteristics of urban centers, but few recent studies have focused on functional dimensions of urban centers. Emerging big data sources provide new opportunities to explore the morphological and functional perspectives of urban spatial structure. This study uses mobile phone signaling data and develops a new methodology to measure urban centers’ functional centrality. The study area focuses on Shenzhen City, which has rapidly transformed from a village into a metropolitan city in the past few decades. As the first economic special zone in China, Shenzhen has adopted a polycentric urban plan since the beginning of the urbanization process. This study explores the spatial employment structure of the city from the morphological and function dimensions. Based on the findings, this study discusses the role of urban planning in forming an urban spatial structure and provides implications for future planning.

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