Jo Dec 15, 2022
Production systems operated in practice consist of repairable components and such systems may mostly be modeled as a direct-parallel system. Thus, analysis of the reliability characteristics of a direct-cold standby system is important in the reliability analysis of the system.
Most of the components for a repairable system are not the same after repair as new ones and component’s lifetime decreases with the increase in the time of use. What is more, the time for repair increases more and more once they stop working, which finally leads to complete failure.
On the assumption that the lifetime and repair time of components follow a geometric process, Kim Man Su, a lecturer at the Faculty of Applied Mathematics, has studied the reliability of several dual series direct-parallel systems in consideration of such decrepitude.
The figure above shows a state transition graph of a system, where a circle stands for in operation and a square means break down.
It is assumed that the system consists of components 1, 2 and 3, and components 2 and 3 make up a dual cold standby system, which is then connected with component 1 directly. Here, component 1 gets priority in repair. There is a repairman. Components 2 and 3 are repaired in order of failure.
The system is a unidirectional closed dual series cold standby system. It means if component 1 fails, the system breaks down.
At the beginning, three components are all new, and components 1 and 2 are in operation and component 3 is under cold standby. When the three components in the system are in good condition, two are in operation and one is under cold standby. The repairman sets to work once one of them fails. At the same time, the standby one begins to work. When the failed one has been repaired, it is put on cold standby until the next failure. If one fails while the other is still under repair, it must wait for repair and the system breaks down. It is assumed that each component after repair is not ‘as good as a new one’.
A deteriorative repairable system will not support constant repair of its components. For a deteriorative repairable system, it seems more reasonable to assume that the successive working time of the system after repair will become shorter and shorter while the consecutive repair time of the system after failure will get longer and longer. Ultimately, it cannot work any longer, nor can it be repaired.
In a dual series cold standby system, after N cycle of component 2, when it finishes working, a plan to replace it with a new one (the same as the first dual series cold standby system) is called N replacement policy.
If the lifetime and repair time of components follow a geometric process in a unidirectional closed dual series cold standby system, the solution of state probability (density) is difficult to present analytically, so replacement cycle N needs to be defined and the characteristics of the system be analyzed.
In order to determine an effective replacement cycle, he studied the stationary conditions of the unidirectional closed system using the transitive property of the Markov chain assuming every state in all possible cases in the system.
The results showed that the proposed mathematical method could be effectively used in different pieces of research of other kinds of queuing models.
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Jo Dec 14, 2022
Hoejang jogori is a piece of clothing whose collar, breast-tie, cuffs and armholes are decorated with strips of cloth different in color from the ground.
Our people have sewn strips of cloth in different colors onto collars, hems, cuffs, etc. over a long period of time. Sewing colored strips for trimming originated from the need to keep their clothes clean by replacing colored pieces of cloth on the easy-to-get-dirty parts as often as they could. Later, the strips developed into a means of adornment, adding beauty to the Korean jackets.
The Korean jacket with colorful strips was divided into two kinds ― samhoejang jogori (those with strips on the collar, armholes and cuffs) and panhoejang jogori (those with strips on one or two parts of them). Samhoejang jogori was usually worn by young ladies as formal clothes for wedding, while panhoejang jogori was worn by the middle-aged. For its elegance, women loved being dressed in it, not just on formal occasions or holidays but for everyday life.
Hoejang jogori is still popular with the Korean women for its smartness and gorgeous harmony of colors.
Pak Sin Jong, researcher at the Academy of Social Sciences
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Jo Dec 12, 2022
According to the characteristics of the subject with geographic objects and phenomena as the main study, Kim Un Hyok, a researcher at the Faculty of Earth Science and Technology, has introduced virtual reality technology to raise the effectiveness of teaching.
The most typical application of virtual reality in geospatial information science is a virtual globe. It is a globe that has digitized information of the earth and all things happening on it.
The virtual globe is a fine tool that enables people to learn about the earth, the world and people’s everyday life. If it is in effective use in geographic information system, it will prove to be helpful to attain teaching aims.
Unlike the past days when he used to give basic knowledge such as definitions and concepts before going into the main point, he showed a virtual globe first to make his students discuss collection and management, edition, analysis and output of geographic information. In other words, he converted his lecture into a question and answer session and let them make virtual visual aids including a virtual globe on their own.
As a result, he could ensure high teaching density and at the same time guide them to give a full play to their abilities for enquiry, design and creation.
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Jo Dec 9, 2022
Ryang Song Ji, the main compiler of “Tonggukyojisungnam” (50 volumes), which was an important part of the geography book of our country, was a well-known scholar who made great achievements in several fields. He started learning at the age of six. From a very early age, he was so clever and good at composing poems that he attracted everybody’s attention. He thought that it was of utmost importance for everyone to be well aware of the geography of their native places and homeland, and that learning and technical research should be focused on both the prosperity of their country and making the lives of common people better.
Possessed of many-sided knowledge including history and geography, he was involved in compiling and publishing several books in the fifteenth century. In fact, almost all the geography books and maps of that time were related to him. Among them, geography part of “Sejong Sillok” (Chronicles of King Sejong) and “Tonggukyojisungnam” played very important parts in writing the geography book in the feudal age of our country. Together with 23 scholars including Ro Sa Sin and Kang Hui Maeng, Ryang Song Ji completed “Tonggukyojisungnam” (50 volumes) in 1481 on the basis of “Geography of Eight Provinces” compiled in 1432, geography part of “Sejong Sillok” compiled in 1454 by amending “Geography of Eight Provinces”, “Sinchan Geography” and “Tongmunson” compiled in 1477. With rich and detailed contents, “Tonggukyojisungnam” is a priceless classic of great value in the historical and geographical study of several fields of our country including society, economy, military affairs, culture, etc. around the fifteenth century.
In addition to it, Ryang Song Ji made several maps that demonstrated the level of the Korean cartology of that time.
As a scholar of noble birth, he presented to the feudal government a “reform plan” several times that reflected his creative opinion on making some changes to the affairs in several fields of the feudal system including military affairs and economy for building up the national power and defending the security of the country.
His exploits for the development of geography performed in those days are being conveyed through generations together with “Tonggukyojisungnam”.
Kim Kwang Jo, researcher at the Academy of Social Sciences
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Jo Dec 8, 2022
Humidity is an important physical quantity in all fields of human life. In recent years, fiber-optic humidity sensors with compact size, high sensitivity and good resistance to chemical corrosion and insusceptibility to electromagnetic interference have been widely studied.
Yu Hyong Su, a researcher at the Semiconductor Institute, has proposed a novel optical humidity sensor which is simple in structure, easy to make and cost-effective with high sensitivity, a wide range of operation, and good safety and reproductivity. It consists of light source, a gap and an acrylic resin film coated on PSD.
Experimental results verified very satisfactory performance of the humidity sensor in terms of its sensitivity, hysteresis, linear response to the humidity and long-term stability.
You can find more information about it in his paper “Widely sensitive optical humidity module by using acrylic resin and a position sensitivity detector” published in the SCI Journal “Optical and Quantum Electronics”.
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Jo Dec 7, 2022
Ri Kwang Su, a researcher at the Faculty of Earth Science and Technology, studied an evaluation method by real problem solution and applied it to “geology information processing” to evaluate the real ability of students scientifically, objectively and quantitatively by combining theory and practice, knowledge and intelligence.
The aim of this method is to improve the creative power, application ability and zeal for study of students and to ensure generalization, objectivity, fairness and quantitativeness of evaluation by combining theory and practice, subject examination and ability test.
This method belongs to objective and open testing methods that can be applied to classroom-teaching and it is the one that estimates students' ability quantitatively and absolutely from the viewpoint of the evaluation type of studying processes.
The gist of this method is to compose test problems and essay tasks so that students' ability can be estimated quantitatively, objectively and scientifically.
To apply this new method, he tried to give lectures upon the principle of improving their application faculties and make test questions and essay tasks on the subject in line with the contents of the subject.
It is an effective method that ensures the attainment of evaluation aim and the consistency of teaching contents and evaluation results thanks to the rational relationships between the contents and forms, evaluation modes and marking of tests and essays, teaching contents and process.
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