Jo Aug 12, 2025
Generally, the film produced by the chemical film process is not as corrosion-resistant as that produced by the anodizing process, and that is why the chemical film process can only be used for the surface treatment of aircraft skins and non-structural parts.
Unlike the chemical film process, the anodizing process can produce a dense and thick porous oxide layer with excellent corrosion resistance performance. For a thicker and denser oxide layer on the aluminum sheet surface, an aluminum sheet should be immersed in a treatment tank with suitable electrolyte and a direct current or an alternating current should be applied to it. The porous oxide layer provides a large wetting area for adhering, thus enhancing the bonding strength of the aluminum sheet.
Chromic anodizing, sulfuric anodizing, hard anodizing and hot etching are the most commonly used surface treatments of aluminum sheets.
Kim Nam Il, a researcher at the Faculty of Materials Science and Technology, has found the most suitable surface treatment by studying the effect of the four different surface treatments on AlMgSi aluminum sheets when they are bonded with an epoxy-based film adhesive.
He performed four different surface treatments on aluminum sheets that were then bonded with an epoxy-based film adhesive in an autoclave to achieve good adhesion. He examined the microstructure of the porous oxide layer on the aluminum sheet surface and its effect on the bonding performance.
The analysis of the failure modes of the bonded surfaces, the peeling strength and the microstructure of the porous oxide layer showed that chromic anodizing of aluminum sheets have the best bonding performance, whereas sulfuric anodizing and hard anodizing exhibit the worst bonding performance.
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Jo Aug 11, 2025
A jottae (a Korean bamboo flute) is a national woodwind instrument from the period of Koguryo. It was also called transverse flute as it is played transversely. It was first made in Koguryo. In Paekje and Silla, they introduced the Koguryo jottae to make several kinds of bamboo instruments. Later, around the period of Koryo and feudal Joson dynasty, it became a major tune instrument. Its mouthpiece is oval and very big, which requires high technical skills to play.
You play the jottae with its head on your left shoulder and with your lips at the mouthpiece. You make vibrato by means of the up-and-down movements of your left elbow connected with the jottae. It is characterized by the gentle, soft, sweet and elegant timbre.
The Korean bamboo flute widely played by the Korean people was improved into three kinds: ordinary jottae, high-pitched jottae and low-pitched jottae, and it developed into the one capable of playing modern music skillfully with its peculiar features unchanged.
The improved ones are made of wood from paktal trees and red sandalwood instead of bamboo, which guarantees scientific accuracy and unity in their making.
Today, the Korean bamboo flute is mainly used for solos and ensembles, and, in particular, it is used as a major instrument for elegant and plaintive tones in the mixed orchestral music of a Juche type.
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Jo Aug 8, 2025
Spraying is a surface treatment technique whereby the heat source such as an arc or gas flame melts the spraying material and the compressed gas injects it to form a coating on the metal surface. Unlike surface alloying, the coating component is never or rarely diluted by the base metal because it melts none or very little of the base material.
In order to coat mechanical components with mechanical abrasions or casting defects on their surface, the self-propagating high-temperature synthesis method (SHS) is incorporated into the oxygen-acetylene flame spaying. Compared to plasma spraying, oxygen-acetylene flame spraying is cheap, but it is not available for materials with high melting points due to its low flame speed and flame temperature. However, combining the oxygen-acetylene flame spraying with the SHS method is the solution.
Therefore, there have been many studies to spray Al-Fe2O3 materials with good internal friction performance, low cost and high melting points by combining the oxygen-acetylene frame spraying and the SHS method. However, they dealt only with the spraying process and the structures and properties of coating layers in the system, but not reactive thermodynamic analyses.
The desired reaction during spraying and the formation of the structure can be found by reaction thermodynamic analysis. Hence, Jegal Tok Song, a researcher at the Faculty of Materials Science and Technology, has formed an Al2O3-Fe composite coating layer with Fe2O3 and Al powder, cheap belongings to the SHS reaction system, and performed a reactive thermodynamic analysis and a simulation of a spraying process.
First, he verified the possibility of reaction by calculating the adiabatic temperature of the system and the Gibbs free energy of theoretically possible reactions. Then, he performed a differential thermal analysis to determine the temperature for reactions. Finally, he determined the optimum spraying conditions by using Fluent.
The results of his study can also be applied to other reaction systems that involve SHS methods for spraying.
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Jo Aug 6, 2025
Sungin Hall is a shrine built at the end of the Koryo age, standing together with Sungnyong Hall by the Pyongyang Students and Children’s Palace.
It was first built in 1325 in the late period of Koryo. It underwent three thorough repairs in 1352 and 1428 and finally in 1954 immediately after the Fatherland Liberation War, to be in the present state.
Sungin Hall, which was originally comprised of 10-odd buildings including the main building, was damaged by the aggressors during the Imjin Patriotic War and the Fatherland Liberation War, as a result of which only the main building, the gate and the monument pavilion survived. The central building alone was moved next to Sungnyong Hall in 1977.
This building for ancestor worship was promoted in its name in 1612 to be called Sungin Hall. It is a precious historical relic that demonstrates the excellent architecture of Koryo, providing a lot of information for studying the architectural history of Korea.
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Jo Aug 5, 2025
In the initial IMO Strategy for reducing greenhouse gas (GHG) emissions from ships, the level of ambition for CII of international shipping was quantified by CO2 emissions per transport work, the average of overall international shipping.
This is a severe rule for ships with only short voyage because the greater the navigation distance is, the lower the CO2 emissions per unit transport work are. In addition, short voyage ships might be evaluated as poor in the CII assessment because of the small transport workday, although measures have been taken to improve energy efficiency. Consequently, all ships will refuse short-term navigation, resulting in a conversion to land transport in some areas. This will lead to an increase in CO2 emissions.
Ri Hyok, a researcher at the Faculty of Shipbuilding and Ocean Engineering, has proposed a relatively fair CII calculation method by introducing a correction factor for an ordinary freight vessel, taking short-voyage and long-voyage into account.
He confirmed the accuracy of correction factors with operational data of ships of less than 35 000 DWT.
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Jo Aug 2, 2025
Pobun Hermitage is a Buddhist temple located on Mt. Ryongak. The present buildings underwent reconstruction during the feudal Joson dynasty.
The hermitage was built during the period of Koguryo, which is proved by the fact that the way of trimming the stones piled for the stereobate is the same as those for Koguryo citadels and that some convex roofing tiles and antefixes were discovered, as well as by the epitaph and other records.
With bluff cliffs in the background, Pobun Hermitage, which consists of five buildings including the main temple, is well suited to the topographical conditions of Mt. Ryongak.
The main temple of the hermitage erected on the raised stereobate is five kans (10.27 meters) long and three kans (6.2 meters) wide.
The hermitage, the precious national cultural heritage associated with the talent of the Korean people, is now in good preservation and care.
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