Jo Sep 6, 2024
Ozone has strong oxidation ability and very strong reactivity with organic and inorganic substances. It also leaves no secondary contaminants, which makes it applicable in a variety of ways in many fields including chemical industry, medicine, light industry, agriculture, water treatment, etc.
With the expansion of application of ozone generators over a long period since its appearance, the power supply of ozone generation has been made in various types and many achievements have been made in the research for power quality improvement.
Nowadays, an ozone generator based on dielectric barrier discharge (DBD) is popular and the high-voltage and high-frequency inverter power supply is essential in power mode.
Hwang Kum Song, a researcher at the Nano Physics Engineering Institute, has proposed a method for a feedback control of the discharge current in a DBD type high-frequency and high-voltage power supply to keep the discharge intensity of the ozone generator constant and to improve the power efficiency.
He mapped the discharge current model of the DBD inverter source, which is subject to strong nonlinearity and model uncertainty, to a dynamic linearization (DL) model to design a model-free adaptive control (MFAC) algorithm, and conducted a simulation on Matlab Simulink. He designed an MFA controller with the control object equivalent to the simplest dynamic linear model.
The strong nonlinearity and model uncertainty inherent in the control objective reduce the control effectiveness of conventional control approaches (PID control or fuzzy-PID control) and complicates the application of intelligent control approaches.
However, MFAC method, which requires no model of a plant and only controls the input and output data of the system, is more effective in constant-current control of the DBD ozone generator. MFA controller based on compact form dynamic linearization is convenient for implementation because of its simple structure and low computational cost. In addition, optimizing the parameters of the model-free adaptive controller can achieve more flexible adaptation of the controller, eliminate most of the overshoot and improve the response speed.
The simulation results showed the improved effectiveness of the model-free adaptive controller compared to the PID controller or the fuzzy-PID controller.
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Jo Sep 5, 2024
Kyongdang was a civilian education establishment of the Koguryo age.
Koguryo people, regardless of their high or low social standings, liked learning, so they built a large house called kyongdang for educating young people including children.
The education at kyongdang was aimed at cultivating patriotism and talent, and courage and strength.
Those who attended kyongdang learnt to read and acquired knowledge of history and other fields day and night.
In addition, they built up their physical strength, training in several military arts like archery, horse riding, swordsmanship, etc.
It has been said that many kyongdang graduates with literary and military accomplishments played a big part in the battles against foreign invaders.
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Jo Sep 4, 2024
Parallel manipulators are closed-loop mechanical structures presenting very good performance in terms of accuracy, rigidity and ability to move large loads. Generally, the mechanism has two platforms: one is attached to the fixed reference frame and the other performs arbitrary motions in its workspace. Some moving legs similar to those of serial robots connect the moving platform to the fixed platform. Spherical joints, revolution joints or prismatic joints connect the elements of the robot to one another.
Recently, much effort has been devoted to the kinematic and dynamic analysis of fully parallel manipulators. The dynamic analysis was usually conducted by analytical methods of classical mechanics in which projection and resolution of equations on the reference axes are written in a considerable number of cumbersome, scalar relations and the solutions are rendered by large-scale computation together with time-consuming computer codes.
Pang Thae Jin, a researcher at the Robotics Institute, has established a new method for inverse dynamic analysis of a 3-DOF parallel manipulator with three actuators using an approach based on the principle of virtual work.
The new approach is far more efficient, and it can eliminate all forces of internal joints and directly determine the time-history evolution of torques and powers required by the three actuators.
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Jo Sep 2, 2024
The 7-storied Hexagonal Tower at Hangbok Temple is situated in Taesong-dong, Taesong District, Pyongyang City, DPRK.
It is 5.35 meters tall.
The planes of major parts of the tower including base stone, platform and body are hexagonal. All the parts are in good harmony and delicately and smoothly shaped.
This unusual hexagonal tower fully displays the appearance of a typical stone tower of the Koryo age. This precious national heritage is in good preservation and care, demonstrating the excellent stone architecture of the Korean people.
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Jo Aug 30, 2024
Stress sensitivity and the elastic outer boundary (EOB) condition have a great effect on the analysis of the characteristics of fluid flow in a reservoir. When analyzing the characteristics of fluid flow, researchers considered the stress sensitivity and the EOB condition separately, not simultaneously. Therefore, errors were inevitable during the analysis of well testing.
Kim Song Chol, a section head at the Faculty of Earth Science and Technology, has established a well-testing model for the DPR, considering the stress sensitivity and the EOB condition simultaneously and presented its semianalytical solution.
First, on the basis of the consideration of the EOB condition and stress sensitivity of permeability (SSP), he built a seepage model for the DPR with the EOB by considering wellbore storage and skin. To solve this model, he changed a nonlinear partial differential equation into a linear form by introducing an effective well radius and applying Pedrosa’s transformation and perturbation transformation. Then, by applying the Laplace transformation, he obtained an analytical solution in the Laplace space, and by numerically inverting it, he obtained a solution in the real space, thus drawing the curves of pressure and pressure derivative (PPD).
By comparing the proposed model with the one with the EOB without consideration of SSP, he verified its effectiveness.
For more information, please refer to his paper “Well-Testing Model for Dual-Porosity Reservoir considering Stress-Sensitivity and Elastic Outer Boundary Condition” in “Geofluids” (SCI).
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Jo Aug 29, 2024
Developing high quality learning contents (LCs) and improving their interactions in online learning with e-learning contents is important for greater cognitive abilities of a learner.
Studies on the interactions in online learning have increased and focus has been placed on its increased effectiveness. However, there has been less discussion on the relationship of LC design to learner’s cognition. In addition, there are few qualitative data on the interactions between a learner and LC, and less has been known about the effectiveness of self-feedback in learning processes on increasing the cognitive abilities of a learner. On the other hand, non-structural interaction brings about negative results to learners and cannot improve learner’s cognition, which means less cost-effective. This clearly shows that the interactions with LCs should be improved for successful online learning and, to this end, LCs with a self-feedback structure be designed to suit the intrinsic features of a learner.
Kim Jang Hak, a section head at the Faculty of Distance Education, has designed LCs with new self-feedback structure by considering the personalized characteristics of a learner and described a method for improving learners’ cognition abilities through improved interactions between a learner and LCs.
Based on the previous research findings on feedback and interaction, he divided the learning object into knowledge unit learning nodes and managed the learning control and appropriate interactions through self-feedback. Then, he conducted an experiment to investigate what improvement was made in the learner’s cognition by putting the proposed method into practical application.
The result showed that the self-feedback is a significant factor that gives positive influence on the learner’s cognition.
You can find the details in his paper “Improving Learners' Cognition through Designing Learning Contents with Self-feedback Structure and Advanced Interaction in Online Learning” in “Informatica” (SCI).
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