Jo Jun 22, 2022
Cast aluminum alloys are quite widespread and they find more and more applications in modern industry such as aerospace, navigation and railway transport thanks to their good mechanical property, castability, corrosion resistance, etc.
Quality indices are a measure to quantify quality of the alloy on the basis of its mechanical properties.
The indices are Q, QR, QC, QD(Q0), QE, etc. Each one has its own unique features and individual one cannot display the overall performance of cast aluminium alloys.
The most representative indices to evaluate their overall performance can be chosen by two methods ― method of correlation analysis between quality indexes and mechanical properties and method of correlation analysis and rank deviation analysis between overall performance scores obtained from quality indices and MCDM method.
The analysis result showed that Q0 proved to be the most representative one of all the indices Q, QR, QC and Q0, and that Q0 can be used instead of MCDMs for evaluation of overall performance of cast aluminum alloys and selection of optimal cast aluminum alloys.
Detailed information about this can be found in the paper “ Method to evaluate overall performance of cast aluminum alloys using most representative quality index instead of MCDM method” presented by Yang Won Chol, a researcher at the Faculty of Materials Science and Technology, to the SCI Jounal “International Journal of Metalcasting”.
...
Jo Jun 14, 2022
Kim Ryul, a researcher at the Faculty of Electrical Engineering, has realized selection of crack insulators from a pile of 10kV pin insulators by data processing of thermal shock sample breaking test and a corona short-circuit nondestructive test device.
Compared with previous selection methods by electric penetration breakdown test, this method provides more safety and lower production cost. In addition, as it uses nondestructive electric tests to sort out crack insulators, the reliability of production pile of insulators can be further improved.
This method is constructed with several stages: determination of size of 10kV pin insulator piles and samples, thermal shock sample destructive test, state decision of pass or pass failure of production piles by processing test data, determination of acceptance probability by quality control software and of the number of faulty insulators, and selection of crack pin insulators by the corona short-circuit nondestructive selection device.
This thermal shock test costs less and provides 1.4 times higher accuracy than the previous electric penetration breakdown test. To estimate cracks in 10kV pin insulator piles, previous binomial distribution was replaced with noncentral t-distribution, which reduced the number of samples to half and improved the accuracy of acceptance probability of piles and the calculation of the number of crack insulators by 1.2 times. Instead of electric penetration breakdown test devices, corona nondestructive test devices were used, which made it possible to select 100% of crack insulators from passed piles.
...
Jo Jun 13, 2022
Mausoleum of King Kogukwon is a tomb with mural paintings for King Kogukwon, 21st king of Koguryo, situated in Oguk-ri, Anak County, South Hwanghae Province. It dates back to mid-4th century and it is also called Anak Tomb No. 3.
The mausoleum, precious heritage of our national culture, is by far the number one of all Koguryo tombs ever known in terms of scale and richness of content of mural paintings. As a world-famous relic representative of the eastern culture in 4th century that gives an impression of an underground palace, it fully demonstrates the high level of might and culture of Koguryo.
It has a side chamber with figure and genre paintings. It is colossal in size ― about 33 metres from north to south, about 30 metres from east to west and 6 metres high. Located on the mountain and merged with it into one, it looks really magnificent like a huge mountain. It consists of a doorway, a front chamber, two side chambers in the east and west of the front chamber, inside chamber, a corridor, etc. that are built of stone semi-underground on the mountaintop cut downward flat.
The entrance facing the south of the doorway is blocked by a standing plain rock. The doorway is 2.17 metres long from east to west, 2.12 metres wide from north to south and about 3.48 metres high. Two stone doors are attached between the doorway and the front chamber. The front chamber is 4.88 metres long from east to west, 2.73 metres wide from north to south and 3.47 metres high. Between the front chamber and the inside chamber stand 3 octagonal pillars and between the two side chambers and the entrance to the corridor stand 2 square pillars, on the tops of which crenelles (layers of "cow's-tongue" ornamentation) or caps are placed.
The inside chamber is 3.8 metres long from east to west, 3.32 metres wide from north to south and 2.8 metres high. The eastern and the northern sides of the inner chamber are connected by an L-shaped corridor. The corridor is 10.13 metres in length, 0.69~0.87 metres in width and 2.5 metres in height. The ceiling of the corridor is supported by double parallel stays.
The murals are painted on bare stone walls. On the walls of the doorway are painted warriors guarding the king buried in this tomb and in the front chamber are found paintings of guards of honour, subakhui (Korean style of martial art using only the hands), singing and dancing. In the west side chamber are seen the scenes where the king, the main character, wearing “Paekragwan” (crown worn by Koguryo kings) and colourful silk robes is conducting state affairs together with civil and military officers, and the queen is being waited by the court ladies. In the east side chamber there are murals of kitchen, meat storage, well, mill, stable, cowshed, coach house, etc. The corridor is decorated with the mural of the main character wearing “Paekragwan” on an oxcart followed by the grand procession advancing majestically under the guard of warriors, civil and military officers, instrumental march music band, ceremonial flags such as “Songsangbon”, “Ttukki”, “Jongjol”, etc. owned only by the Koguryo kings. Each mural is different in painting technique.
The best-painted ones of all the murals are those with main characters in them. Although they have the limitation of the period when the portraits of the main characters were painted differently in size according to their social standings, they are invaluable ones that ascertain the very beginning of portrait painting in our country. The procession of several columns overlapping each other is portrayed skillfully by the technique of a bird’s-eye view. Demonstrating that its technique of picture painting was contemporarily of the highest level, this mural, in terms of the number of characters of over 250, the size and the complicated and colourful scenes, ranks first of all the murals in our country and it is a leading masterpiece that holds an important position in the history of the world fine arts.
At first there was a huge amount of valuable objects made of gold, silver, copper, iron, jade, etc. in the mausoleum, but at the time when it was discovered, only earthenware like plates, small bowls, pots, etc. was found due to grave robbery a long time ago.
The mausoleum is a precious cultural heritage that vividly shows the history, custom, architecture, art, music, dance, weapons, armament, etc. through the structure of chambers and the murals in them.
The architecture of bolsters and the murals in the mausoleum are the precious national cultural heritage that clearly shows the wisdom and resourcefulness of the Korean nation as well as the high level of its cultural development and world-famous relics representative of the contemporary eastern culture.
...
Jo Jun 11, 2022
Ro Yong Sim, a researcher at the Faculty of Electrical Engineering, has applied, in her subject Servo Motor Design, a new examination method in which students are given questions in multimedia and allowed to consult references, in contrast with traditional examination methods in which only theoretical problems and complicated design calculations were given, in order to evaluate correctly their theoretical and practical abilities to design different servo motors.
Primarily, in order to evaluate students’ design ability she gives questions for the characteristic parameters of servo motors whose dimensional structures difficult to be expressed in words are shown in movies and images and allows them to consult all available references to calculate them.
The questions are made to be solved only when they have gone through several steps of calculation while grasping the correct meaning of all the variables in complicated design equations.
Then the students, on the basis of the decision of what kind of servo motor it is from the images and movies, calculate the characteristic parameters such as time constant or inertia, which makes it possible to evaluate their design ability for a particular object.
Secondly, she presents questions in images to evaluate the practical ability to understand design plans.
In other words, she blanks or makes errors in some parts of the plan of a servo motor shown in image to make the students correct them.
The students are supposed to write on their exam paper which parts contain errors and how the errors should be corrected.
Thirdly, she uses questions to estimate the computer aided design ability of the students.
For example, to test the analysis ability of the students by Ansoft Maxwell software, she distributes to students’ computers a program file which has analysis conditions beforehand and encounters an error because of some mistakes made during modeling and analyzing. The students come to use some software tools to correct the errors. She makes them write or draw on the paper the cause of errors, the resultant parameter values and graphs.
Fourthly, she uses multimedia for questions to estimate their theoretical knowledge, too.
For example, while showing a movie in which a three-phase hybrid-type stepper motor is rotating, she pauses the movie at any moment and asks students to draw an equivalent magnetic circuit at that point. This enables her to evaluate if they have a correct understanding in detail of the operating principle of the stepper motor.
Finally, she uses multimedia to evaluate the creative ability of the students.
For example, in the past she used to ask, “What methods to decrease the cogging torque of a permanent magnet electric machine are there?”, but now she first shows the parts and assemblies of a permanent magnet synchronous motor in multimedia and then gives questions like how this motor could decrease cogging torque and what else could be done for that.
So she can evaluate on the basis of a particular object if the students grasp the theory and know how to apply it to the practice.
Besides, by giving a task to design permanent magnet about that object, she could test the creative design ability of the students in a comprehensive way such as if they select the optimal pole embrace to minimize the cogging torque, if they set reasonable air gap, if they choose proper material for permanent magnet or if they rationally design dimensions like the width and the thickness of the poles.
She makes such questions with PowerPoint software, sends them to every computer of the students, and allows them to use all the materials such as computers, textbooks and reference books during the test while she prevents them from exchanging information through the network.
Applying this testing method she has been able to correctly evaluate the practical ability as well as the theoretical knowledge of the students and fully stimulate the interest in their study.
...
Jo Jun 7, 2022
Koguryo, first feudal state in our country, lasted for nearly a thousand years from 277 B.C. to 668 A.D., holding the central position and playing a leading role in the development of history of our country.
The founder is Sejo, King Tongmyong (Ko Ju Mong). When he became the lawful successor to the king of Kuryo, he formed a new feudal system in 277 B.C. and named it Koguryo. He had its capital Jolbon Castle (castle on the mountain) built within a few years and merged several neighbouring countries in ten years’ time, enlarging Koguryo into a fairly big country that stretched 2 000 ri (1 ri = about 393m) from east to west.
The capital moved from Jolbon Castle to Kuknae Castle (Jipanhyon) in 3 A.D., to Pyongyang Castle (Mt. Taesong area) in 427, to new Pyongyang Castle (Jangan Castle) in 586. Hwando Castle 2 (North Pyongyang Castle, Ponghwang Castle) and South Pyongyang Castle (Mt. Jangsu area, later Han Castle) became the second capitals between the late 4th century and the early 5th century, forming a system of 5 capitals.
With rapid progress in several fields of politics, military affairs, economy and culture after the establishment, Koguryo emerged as one of the most developed countries in Asia in those days and demonstrated its prominently advanced culture out to the whole world.
For some centuries B.C. and A.D., feudal relationship was consolidated and developed and the whole well-regulated feudal system was established in Koguryo, which became the main framework of the state and social systems of subsequent several feudal states in our country as well as Paekje and Silla.
From the end of the 2nd century B.C. Koguryo people loaded with a high sense of patriotism and military spirit played the role as a fort and a shield to defend the entire land and fellow countrymen by repulsing foreign forces of aggression.
Koguryo set territorial unification as its important policy and put a lot of effort to realize it. As a result, in the west it merged several small countries in the southeast of Ryodong Peninsula by the 70s in the first century, in the southwest the northern part of Raknangguk, and in the east and the south Kaema, Kuda, Jona, Juna, East Okjo and other 7 small countries. In the north it defeated Ancient Puyo at the end of the 3rd century B.C. and took several small countries subject to Puyo under its control. After the establishment of Later Puyo feudal state in the early 2nd century B.C., it took control of the southern part of Jilin area and merged Kalsaguk.
The struggle of Koguryo for territorial unification was carried out along with anti-aggressive struggles. In 529 Koguryo extended its territory to the faraway bounds of Asan Bay, which brought unification of Three Kingdoms to the verge of completion in the first half of the 6th century.
Moreover, Koguryo developed various fields of its economy and culture, exerting a great influence upon the development of economy and culture of the neighbouring countries of the same blood and spreading its advanced culture even abroad.
In summary, Koguryo was a strong country with vast territory and advanced culture, which is a great pride of Korean nation possessed of a time-honoured history, ardent patriotism, strong national self-respect and unexcelled resourcefulness and wisdom.
...
