We investigate the impact of economic policy uncertainty (EPU) on corporate inventory holdings in China over the period 2007-2017. We find that EPU leads firms to significantly reduce inventory holdings and this effect is particularly pronounced among non-state-owned enterprises. The adjustment of inventory holdings enhances firms' operating and market performance consequently. In addition, firms with greater financial constraints or stronger external governance are more affected by EPU. Further exploration shows that EPU induces high precautionary cash holdings, which crowds out inventories. Our results illustrate that firms reallocate between inventories and cash to cope with uncertainty associated with economic policy changes.
Ancient ivory, from the Chengdu Jinsha and Guanghan Sanxingdui sites in China, has been buried for several thousand years. In order to determine the degradation mechanisms and to provide a scientific basis for protecting them, these ancient ivory samples have been compared with modern ivory using infrared spectroscopy in the frequency range 400À4000 cm À1 . By combining chemical analysis data we compare the crystallinity and crystal chemistry of the apatite component, as well as the structural characteristics of the ivory. These investigations showed that the ancient ivory consists almost entirely of hydroxyl-carbonate apatite as the predominant phase. Compared with the modern ivory, the PO 4 3À and CO 3 2À bands are stronger, the PO 4 RF values are obviously greater, and an extra OH À band at 3569 cm À1 is observed in the ancient ivory. These results indicate that there is a greater degree of apatite crystallinity in the ancient ivory and also imply that there has been incorporation and recrystallization of CO 3 2À in the apatite during burial. Positive correlations have been found between the apatite crystallinity, CO 3 2À and OH À ion contents, and burial time. The organic matter in ancient ivory has been lost or decomposed as the organic bands (e.g. at 1238 cm À1 and 1337 cm À1 ) have disappeared. This may be the main reason that ancient ivory is easily dewatered and readily friable after being unearthed.
A multisection step-impedance honeycomb absorbing structure is investigated both theoretically and experimentally. Excellent intrinsic impedance matching and low reflection are realized by providing a step-impedance transition between air and metal in the microwave band. The wideband absorption mechanism of the honeycomb absorbing structure is analyzed using a step-impedance model, and the particle swarm optimization algorithm is used to obtain the optimal step impedance. Two absorbing structures were simulated: The double-layer structure had an absorption frequency band of 3.9–12.4 GHz and a thickness of 9 mm, and the triple-layer structure had an absorption frequency band of 2.2–12.4 GHz and a thickness of 15 mm. The measured reflectivity values were consistent with the calculated results, thereby confirming the validity of our designs for the absorbing structure.
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