• Korean Journal of Heritage: History & Science
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• v.56 no.2
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• pp.48-60
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• 2023

Although foxtail and broomcorn millet have been cultivated since the Neolithic Age on the Korean Peninsula, there have been few studies on how the importance of millet cultivation changed over time. The discovery of millet has been rare in the Mahan-Baekje villages in the Jeonnam region, and archaeological discussions on ancient farming have centered around rice farming. However, a large amount of millet was found at the Osan site in Bongrim-ri, Jangheung, showing that the tradition of millet cultivation continued during the AD 3-4 centuries. In contrast to rice farming, which requires low-lying wetlands, hot and humid summers, and a large labor force, millet cultivation has few restrictions in terms of growing environment and labor mobilization. Regarding harvesting seasons, the crops at the Osan site can be divided into fall harvesting (rice, legumes, millet) and summer harvesting (wheat). Regarding field locations, the crops are divided into wetland crops (rice) and dryland crops (wheat, legumes, millet). The operation of the dual agricultural system contributed to subsistence resilience and agricultural production, making it possible to effectively manage social and climatic crises.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.6
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• pp.601-609
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• 2000

Direct torque control(DTC) of AC motor has the fast torque and flux dynamic responses even though it has very simple scheme to implement. However, DTC do not show good performance at low speed range with conventional open loop stator flux observer when stator resistance varied. Therefore, authors propose a new nonlinear stator flux observer in order to estimate the stator flux of induction motor at low speed and show its simulation results.