Jo Jun 6, 2025
Industries require conversion of alternating current of one voltage into another in many fields including electrical heating, lighting control and motor speed control.
Electronic transformers are direct AC-AC converters, which are used in various applications including cranes, turbines and elevator AC motors. Commonly used transformers are heavy with the core and windings, and they need large installation areas. In addition, they cause a large amount of loss due to iron loss even at no-load.
Electronic transformers operated by PWM control have the following advantages compared to conventional ones. First, their volume and weight are 50% and 30-40% of conventional ones of the same capacity, respectively. Second, conventional ones without control functions affect the other side when a short circuit or fault occurs on either input or output, but electronic transformers have a circuit-off function in the event of an accident. Third, by slowly increasing the output voltage at the time of turn-on, they can reduce inrush current or voltage shock into the load, and the addition of control functions can ensure power-off at no-load and compensation for non-sinusoidal input voltage.
Based on the principle of a boost DC/DC (direct current) converter, O Yong Hun, a researcher at the Robotics Institute, has described the advantages of a boost-type electronic transformer of light weight and small volume with protection function during the fault, and constructed the main circuit on a hardware basis so that it can operate like a conventional transformer, and then he has investigated the operation principle, control mode and energy conversion process when the devices are switched on and off.
In addition, he has constructed the main circuit and control system on MATLAB, and investigated the characteristics of the simulation waveforms at each tapping point. On the basis of the correlation between each factor, he has investigated the PWM (Pulse Width Modulation) control scheme for a reasonable parametric design to meet certain load conditions and for harmonic cancellation.
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Jo Jun 4, 2025
At present, various methods of estimating Quality of Service (QoS) of path transmission are in use, but they have following problems.
Firstly, the problem to estimate transmission QoS of multi-path must be settled. Multi-path transmission mode can be used at the time of transmitting real-time media based on Internet Protocol (IP) network. Most of the existing methods deal with the states of delay, jitter and packet loss between two ends, and it is unknown which path such parameters are from. Hence, estimation of QoS of multi-path transmission is important.
Secondly, instruments for QoS dynamic estimation should be prepared. When there is a change in path QoS, the existing statistical analysis instruments cannot estimate transmission QoS in real-time. Hence, QoS dynamic estimation instruments are needed.
Thirdly, path QoS must be comprehensively estimated. Indexes of QoS estimation include delay, jitter, band, packet loss rate, etc., which need comprehensive estimation.
On the basis of recent research on QoS estimation of transmission path, Han Ryong Ho, a researcher at the Faculty of Communications, has proposed a method for QoS estimation in multi-path transmission, and conducted a dynamic estimation analysis for real-time estimation to verify its effectiveness.
The proposed method is effective for dynamically and comprehensively evaluating the QoS of multi-paths between stages in an IP network.
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Jo Jun 3, 2025
Nowadays, with the development of positioning technology, people have become able to obtain the position information of objects in the global range easily, more accurately and in large quantities. In order to reduce the amount of information about the trajectory of moving objects or the location of geographical objects, it is necessary to simplify the polyline consisting of nodes representing the location information.
The Douglas-Peucker (DP) algorithm is known as an accurate and efficient one for simplifying polyline. In order to simplify the trajectory of moving objects in the global domain with DP algorithm, geodetic distance computation in spherical space is necessary.
In the implementation of the DP algorithm on the Earth’s ellipsoid, it is impossible to avoid spending much time on geodetic distance computation, and the main problem is a huge computational effort.
Kim Song Chol, a section head at the IT Institute, has investigated the performance of DP algorithm in spherical space for trajectory simplification of moving objects.
He proposed a method of using geodetic coordinates as spherical coordinates and evaluated its accuracy. The geodetic distance error was about 0.22~0.55% of the maximum geodetic distance. With this error, the results of implementing the DP algorithm in spherical space have been experimentally found to be more accurate. In addition, the computational speed has been proved to be very fast and applicable to the global scale.
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Jo Jun 2, 2025
The Elephant Rock of Pidan Island is a natural monument located in Sindo County of North Phyongan Province.
When the sea water entered the Korean West Sea area at the end of the fourth glacial period, the rocks on the relatively high hills exposed above the sea formed an extraordinary topography by a long time of abrasion and weathering.
The rock has been called Elephant Rock as it resembles an elephant.
The rock is 40 meters long and 15 meters high, with the top of 8 meters in width.
The “trunk” is 9 meters round.
At the “head” of the rock is a small rock resembling an “ivory” and in the middle of the “trunk” is a small hole. Grass is growing on the rock.
The rock is submerged and exposed by the tide. When it is submerged, it looks like an elephant swimming in the water, and when it is exposed, it looks like being caught in the marshland.
The Elephant Rock, which is of significance in studying the change in the nature after the formation of the Korean West Sea, is a natural monument adding beauty to the beachscape.
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Jo May 30, 2025
The time-dependent Ginzburg-Landau (TDGL) equations are a useful computational tool for characterizing the spatiotemporal variance of an order parameter that represents the phase transition in mesoscopic type-II superconductors. Especially, they are used to simulate the dynamics of magnetic vortex for designing superconducting materials with high critical current density.
Therefore, simulation of type-II superconductors using TDGL equations is essential for understanding magnetic vortex dynamics and studying superconducting critical characters such as critical current density and critical magnetic field. Numerical simulations for it are conducted by the finite difference method (FDM), the finite element method (FEM), the lattice Boltzmann method (LBM), etc.
Ryu Yu Gwang, a researcher at the Faculty of Physical Engineering, has investigated the influences of surface defects on the motion of magnetic vortices in a mesoscopic type-II superconductor with randomly distributed pinning centers through the simulations of TDGL equations by using COMSOL Multiphysics.
Two kinds of surface defects are located in the boundary: one is pinning centers and the other is geometric defects along with pinning centers.
In the simulation, he analyzed the magnetization curves, the vorticity and the density of superconducting electrons for both different contents of pinning centers and various geometric defects.
For the pinning centers as surface defects, the maximum magnetization values as a function of the contents exponentially decrease, and the field where the first vortex penetrates and the field where the complete transition from superconducting to a normal state in the system occurs are reduced.
For the geometric defects as surface defects, the density of superconducting electrons and the magnetization curves depend on their size and form. In addition, a threshold in the size of geometric defects in which the motion of vortices and vorticity change, exists.
You can find the details in his paper “The Influence of Surface Defects on Motion of Magnetic Vortices in Mesoscopic Type-II Superconductor with Randomly Distributed Pinning Centers” in “Journal of Superconductivity and Novel Magnetism” (SCI).
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