Jo Jan 13, 2025
Ocha Rock is on the south-west shore of Lagoon Monggum tens of kilometers away from the town of Ryongyon County, South Hwanghae Province, DPRK.
Jangsan Point is the extension of the Pultha mountain range, forming a peninsula. Jangsan Point was formed by the abrasion of quartzite.
The singular Ocha Rock was also formed by such phenomenon. On the shore are standing some cliffs as high as ten to thirty meters. Ocha Rock is twelve to fifteen meters tall and about ten meters round in its bottom.
Ocha Rock is made up of regular layers.
This rare rock formed by abrasion and weathering is of great academic significance and also of great rarity on the coast of the Korean West Sea.
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Jo Jan 10, 2025
Time delay is one of the common cases in industrial processes such as chemical and metallurgical industries. The controlled value cannot reflect the dynamic change of systems under disturbances because of the existence of time delay. It also results in significant overshoot, longer settling time and even instability of the system. Therefore, the time-delay system (TDS) is more difficult to control.
A lot of control methods have been proposed to overcome the impact of time delay. The complexity of time-delay systems such as long time delay, nonlinearity, stochastic uncertainty and multivariable coupling characteristics limit the application of the existing control theories and methods to actual systems.
ADRC (active disturbance rejection control) is an effective method to solve the control problem of complex structure (nonlinearity, uncertainty, coupling, etc.) systems. The core idea of ADRC regards the integral form as a standard form of feedback system. System dynamics different from the standard form are treated as total disturbance including internal disturbance and external disturbance. A complex system with full disturbance, uncertainty and nonlinearity can be reduced to a linear, canonical form.
Several control strategies based on ADRC have been proposed to handle time delay. According to those strategies, it can be concluded that time delay parameter τ is of vital importance. However,τ may be a time-varying parameter changing with working conditions in real industrial processes.
Kim Ha Su, a researcher at the Faculty of Metal Engineering, has proposed a predictive active disturbance rejection control with adaptability (AD-PADRC) to solve the control problem of a time-varying delay system.
The proposed method is based on the integration of a PADRC and an estimation module for adaptive delay. First, a time-delay system is controlled by PADRC. Then, the time-varying delay is estimated via correlation technique. The minimum variance principle is used as a benchmark to monitor the control performance of a time-varying delay system under AD-PADRC.
The simulation results have proved the efficiency of AD-PADRC when the time delay changes on a large scale.
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Jo Jan 8, 2025
More than ten old Kwangmyong Zelkova trees are growing by Jogye Gate of the Sogwang Temple about twenty kilometers north of the seat of Kosan County, Kangwon Province, DPRK.
These trees are said to have been planted in 1386, when the Sogwang Temple was being built.
The largest one is 27 meters tall, with the root collar of 9.8 meters round, the chest-height of 8 meters round and the canopy of 25 meters in diameter. The smallest one is 12 meters tall, with the root collar of 2.4 meters round, the chest-height of 2.3 meters round and the canopy of 8 meters in diameter.
These large old trees are designated as a living monument and in good preservation and care as they are of academic and educational significance and add beauty to the Sogwang Temple.
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Jo Jan 7, 2025
Induction heating (IH) converters commutate close to resonant frequency to supply maximum power to the workpiece. Therefore, the correct identification of the tank’s resonant frequency is a matter of vital importance in most IH converters. Detection of resonant frequency is based on the calculation of the phase-shift between two electric variables. In order to control this phase-shift between two electric variables, most IH converters use a PLL system.
Most PLL systems used in IH converters are analog PLLs that use integrated circuits from the CD4046 circuit family and analog low pass filters. Although analog control has demonstrated to be effective and accurate, it is less flexible and robust to the degradation of the components than digital control. Due to the advantages of digital control presented above, DSPs or field-programmable gate arrays (FPGAs) have been used to implement PLLs. But as hardware components are used, the change of components is needed in the case of changing parameters. In software PLL systems, many of the parameters used during the control, like frequency, dead time or filters, can be adjusted with no changes in hardware.
Kwon Chang Hyok, a researcher at the Faculty of Mechanical Science and Technology, has proposed a method for implementing the resonant frequency tracking control, the main control in IH systems used in various sectors of the national economy, by using a software PLL algorithm, conducted a simulation to evaluate the stability and reliability of control, and verified them through several experiments in the IH system with LLC.
The proposed software PLL algorithm can be applied to induction heating systems as well as to various fields where phase-shift control of both signal waveforms is necessary.
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Jo Jan 4, 2025
Among the rare and beautiful natural monuments of our country is the Isonnam Falls.
It is in the Chonthae Valley of Mt. Myohyang, a superb scenic beauty.
It was called fraternal falls as the waters had been falling in parallel with each other like good brothers for a long time.
In May, 1981, Chairman
Since then, it has been called “Isonnam Falls”.
The falls are 22 meters in height, and 6 to 10 meters and 4 to 8 meters in width, respectively.
The waters fall along the inclined rock, at the protrusion of which they spout forward.
At the bottom is a three-meter-deep pool hollowed by the waterfall.
Isonnam Falls, whose waters fall vigorously in two lines as if competing with each other, is a precious living monument that adds beauty to the natural landscape of the area for its peculiar and beautiful appearance and serves as a cultural resort for the people.
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