Jo Aug 2, 2023
“Tonggukjiriji” is a book of history and geography written in 1640 by Han Paek Gyom (1552―1615), one of the early realist scholars. Ascertained in the book are the ancient history and geography, and the territories and the locations of capitals, mountains and rivers, fortresses, etc. of medieval feudal states in our country.
The author employed a new positivist approach for his book. In other words, he clarified the merits and demerits of the existing historical materials and theories and gave his opinion of them in order to give a correct explanation of the history and geography of the ancient and medieval states existed in our country.
The book is largely divided into three parts ― the first part deals with the territory of ancient Korea; the second part ascertains the capital, territory, topography and fortresses in the period of the Three Kingdoms including Koguryo, Paekje and Silla; the third part covers those of Koryo.
The book has extracts of geographical records of ancient and medieval states of our country from documents at home and abroad and the author’s opinion between them, which give correct solutions to a number of main historical and geographical issues.
Based on the historical books by feudal historians who worshipped great powers, “Tonggukjiriji” reveals some incorrectness. However, it deserves to be one of the precious national geographical legacies as it is written in the way of seeking truth from the fact.
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Jo Jul 31, 2023
Direct and inverse scattering problems play a central role in areas such as radar, sonar, geophysical exploration, and nondestructive testing and they have been widely studied in recent years. In particular, the uniqueness and existence of direct scattering problems, the reciprocity relation and completeness of electric far field patterns, etc. are basic in the inverse scattering theory.
In most applications as well as in geophysical exploration and nondestructive testing, it is, in general, assumed that the scattering obstacle is buried in a piecewise homogeneous medium and is partially coated by a dielectric. For example, underground mines and submarines are embedded in a piecewise homogeneous medium with air-earth and air-water interfaces and they consist of metallic and nonmetallic parts.
Kim Yun Chol, a section head at the Faculty of Applied Mathematics, has studied uniqueness and existence for a direct electromagnetic obstacle scattering problem in a piecewise homogeneous medium, some properties of a scattered field and a far field pattern, including boundedness, reciprocity relation and completeness, where it is assumed that the obstacle is a partially coated perfect conductor and the incident field is given by the electromagnetic plane wave.
He has conclusively proved that the electric far field pattern of the solution of the scattering problem of the electromagnetic plane wave as well as uniqueness and existence for the solution of the direct problem of scattering of time-harmonic electromagnetic waves by a partially coated obstacle buried in a piecewise homogeneous medium satisfies the reciprocity relation, and that the set of electric far-field patterns is complete in a Hilbert space.
These results are of great significance to the study on the solution of inverse electromagnetic scattering problems, i.e. determination of the location, shape and physical property of obstacles from the knowledge of electric far field patterns.
For further information, please refer to his paper “Electromagnetic wave scattering by a partially coated obstacle in a piecewise homogeneous medium” in “Mathematical Methods in the Applied Sciences” (SCI).
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Jo Jul 27, 2023
Analytic hierarchy process (AHP) is a well-known attribute weighting method in multi attribute decision-making. Its major requirement is to satisfy the consistency of pairwise matrix (PM).
To meet these requirements, Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, proposed a new consistency improvement method of PM based on consistency ratio (CR) decreasing rate. In this method, the CR decreasing rates of all the PMs reconstituted by replacing all elements of the PM with the lower and upper neighbouring 9-point scales are calculated, and an element with maximum CR decreasing rate is found before it is modified to its lower or upper neighbouring scale.
Then, he developed a third order approximate polynomial for random consistency index by least square method. It enables determination of the RI value according to the number of attributes without a numerical table.
Finally, he proposed a final PM determination method and a final attribute weighting method with decision makers’ levels in consideration, on the basis of the CR values of individual PMs, when several decision makers perform their own pairwise comparisons.
With two numerical examples, he tested the performances of the proposed and some previous consistency improvement methods.
The results demonstrate that the proposed method improves the consistency of PM better and faster with smaller amount of modification than that of the previous methods, while it modifies the elements of the PM to 9-point scales necessarily.
He has applied the proposed method to hip joint prosthesis material selection to verify that the proposed method may be widely used in practical applications of AHP.
More information about this is found in his paper “Consistency Improvement Method of Pairwise Matrix Based on Consistency Ratio Decreasing Rate and Attribute Weighting Method Considered Decision Makers’ Levels in Analytic Hierarchy Process: Application to Hip Joint Prosthesis Material Selection” in “Mathematical Problems in Engineering” (SCI).
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Jo Jul 26, 2023
Attention to ship energy efficiency and CO2 emission is significantly increasing.
Both are related to fuel consumption and they can be assessed by ship energy efficiency operational indicator (EEOI).
Jon Min Hyok, a section head at the Faculty of Shipbuilding and Ocean Engineering, has developed a formula for estimation of an operational carbon intensity indicator (CII) and an optimal model of ship’s route and operational speed to minimize the EEOI with navigational environment and ship’s safety in consideration.
He developed a formula for estimation of CII, assuming that it is a function of ship’s main particulars such as block coefficient, and the ratio of operation speed to design speed of the ship.
For navigational environment, he considered wave and wind, which greatly influence ship’s performance including resistance and seakeeping.
For ship’s safety, he considered motion sickness incidence (MSI), one of the seakeeping indices.
Particle Swarm Optimization (PSO) algorithm was adopted to solve the model.
He illustrated the proposed method with a numerical example, comparing with full-scale data. The comparison results showed the proposed method can effectively reduce CO2 emission and improve ship energy efficiency.
If further information is needed, please refer to his paper “Optimization of ship energy efficiency considering navigational environment and safety” published in “Proceedings of the 5th International Conference on Numerical Modelling in Engineering (NME 2022)”.
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Jo Jul 24, 2023
Although there are many advantages in SEM measurement methods at ultra-low and low accelerating voltages, it is very important to select a proper accelerating voltage in a wide range from ultra-low accelerating voltage to high one (30kV) according to the purpose of observation of samples.
Studies on imaging of CNTs/polymers have been made within 0.3~5kV of accelerating voltages by FE-SEM with an in-lens detector, but few studies on observation of the surface microstructure of CNTs were conducted by SEM equipped with standard second electron detectors.
Pak Il Man, a section head at the General Assay Office, has performed a theoretical analysis on observation of the microstructure of CNT surface and observed the image of microstructure of CNT surface by Quanta 200 SEM, thus proposing a new method for selecting a proper accelerating voltage.
First, considering the theoretical resolution of Quanta 200 SEM and the size of electron-CNTs interaction range according to acceleration voltage, he made a theoretical study on selection of a proper accelerating voltage.
Second, he performed an observation of SEM images of CNTs at various accelerating voltages.
The effects of energy of the incident electron on the size of the electron-CNTs interaction range and the resolution of SEM were theoretically investigated. As a result, in the case of microstructure observation of CNTs surface by SEM, the most proper accelerating voltage was in the range of 5~10kV.
Through the experiments based on it, he found that the accelerating voltage of 7.5kV enables us to get the sharpest image of the microstructure of CNT surface.
More information is available in his paper “Optimization of the Accelerating Voltage in the Fine Structure Observation of Carbon Nanotube Surface by SEM” in “International Journol of Research and Scientific Innovation” (EI).
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Jo Jul 22, 2023
Hong Won Chol, a researcher at the Faculty of Electrical Engineering, has developed a high-power induction channel furnace (ICF) for melting steel.
Induction channel furnaces (ICF) are widely used for melting, superheating and heat preservation of ferrous and nonferrous metals because of their low power consumption and operation cost. However, thermal stresses in the refractory channel caused by high temperature, premature erosion of the channel due to the flow of molten metal, and failure of the inductor make it difficult to repair them.
He proposed a design of a three-phase channel and an inducer of a new type of ICF for steel melting, and analyzed temperature distribution of the channel by coupling simulations on electromagnetism-heat-fluid, by COMSOL Multiphysics 5.4 and Taguchi method.
An induction channel furnace (ICF) has been widely utilized for melting, refining and heat preservation of metal owing to its advantages such as higher power factor, less power consumption and less stirring of molten metal because the magnetic induction line follows the closed core.
In general, ICF is composed of induction units with iron core, an inductor winding, a channel, and a metal pot. The induction units are assembled verticality to a furnace body, and are separable when the furnace is under repair. The induction units of the proposed ICF are of horizontal type or inclination type, and have no need for separation, so it is easy to repair.
The proposed furnace provides 1 200kW of power, 1.5t/h of output, 1 000V of voltage of inductor (primary winding), 750kW•h/t of power consumption and 4h of cycle of production turns.
This type of furnace, when introduced to the production and refining of steel, cast iron and nonferrous metal, might bring a large profit in operation by saving electrical energy and improving the quality of metals.
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