Jo Nov 14, 2023
Al-Si alloys are widely used in producing precise wear-resistant parts, such as air condition compressors, automobile engine pistons and cylinder bodies in automotive industry and machine-building industry due to the best cast ability among cast aluminum alloys. Especially, hypereutectic Al-Si alloys are rich in silicon. Therefore, they have some advantages such as small coefficient of heat expansion, good resistance to wear, high dimensional stability and lower casting cost.
At the same time, they have some disadvantages of lowering mechanical properties by primary crystal silicon as rough polygon or piece layers unless modified treatment is not enough in crystallization process because of high content of silicon.
Al alloys containing a trace of rare earth metal have high strength, hardness, wear resistance, corrosion resistance and electrical conductivity.
Preceding researches were mainly conducted on the effects of rare earth metal on the mechanical properties of Al-Si alloys.
Ri Hyon Mo, a researcher at the Faculty of Metal Engineering, has investigated the effects of Al-10RE master alloy as grain finer on the tensile strength, elongation percentage and resistance to wear of AiSi19Cu2주. Al-10RE master alloy was used as grain finer of AiSi19Cu2주.
The tensile strength, elongation percentage and resistance to wear of Al-Si hypereutectic cast alloy increase with increase in additive amount of Al-10RE master alloy up to 5%, but they decrease over 5%. After heat treatment, the tensile strength and elongation were 296MPa and 0.84%, respectively, when the additive amount of Al-10RE master alloy was 5%. They increase by 24.4% and 44.8% respectively more than AiSi19Cu2주 without addition of Al-10RE master alloy.
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Jo Nov 11, 2023
A changsaenap is a peculiar woodwind instrument based on a saenap (a Korean brass wind instrument). It was born in the course of development of national instruments under the wise leadership of our Party.
It satisfactorily preserves the features of a saenap in terms of shape and sound quality, supporting the characteristics peculiar to our national instruments.
On the pipe are some finger holes for whole tones and half tones, and some keys.
Compared to a saenap, a changsaenap makes a wider range of and softer sounds.
Such characteristics make execution of folk trills, staccatos, vibratos, etc. successful. It is widely used as a solo instrument.
In addition, it highlights national characteristics in orchestral music and ensembles, and it is effective in playing appealing pieces.
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Jo Nov 10, 2023
Core and Weber set are the most important set-valued solution concepts in TU-games. The core is a set of efficient payoff vectors that satisfy coalitional rationality i.e., a coalition receives at least its own worth, while the Weber set is a convex hull of all marginal vectors. In TU-games, core is always contained in Weber set. Furthermore, a game is convex if and only if its core coincides with its Weber set.
Inclusion of Weber set into core plays an important role in studies of stability of the Shapley value (inclusion of the Shapley value into the core) because the Shapley value is defined as a mean value of all marginal vectors.
O Un Suk, a lecturer at the Faculty of Applied Mathematics, has proved the stability of the extent/intent Shapley value using the inclusion of the extent/intent Weber set into the extent/intent core in games on concept lattices.
In games on extents, she introduced extent Weber set, newly defined strong convexity, and proved the inclusion of the extent Weber set into the extent core under this condition. Similarly, she proved that the intent Weber set is included into the intent core under the weak concavity in games on intents. Finally, she studied the relation between the game on extents and the game on intents, and derived a sufficient condition for stability of two Shapley values.
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Jo Nov 9, 2023
“Taedongjiji”, also called “Taedongbangyogo”, is a geography book of our country. It was written in the middle of the nineteenth century by Kim Jong Ho, a geographer and cartographer of those days. It is in 32 volumes and 15 books.
It was written at the same time as his republication of “Taedongyo Map” in 1864 reflecting the demand of the times concerning the development of commerce and transportation in our country in the nineteenth century.
The book contains a detailed description of about 40 items by counties and districts such as the statistics of population, disposition and power of army, kind and number of ships, customs, taxes, etc., all of which were impossible to show on the map.
The first part of the book shows a table of contents and a list of 65 references. Volume 1 is about the capital. Volumes 2 to 24 deal with the geography of 8 provinces of the country. Volume 25 covers mountains and streams and Volume 26 is about national defence. Volumes 27 and 28 are on transportation and communication each. Volumes from 29 to 32 give the historical geography of territory changed over the period from the ancient times to the Koryo dynasty.
The book is organized in a new system on the basis of the new practical data the author obtained from his field surveys over a long period of time and a great number of references.
In terms of system and description, “Taedongjiji” could not pass the limit of feudal stereotype and facts enumeration but it still serves as one of our country’s geographical legacies with its own characteristics as a modern geography book.
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Jo Nov 7, 2023
Game theory is a set of algebraic models to investigate behavior conflicting with each other. In practice, event players often have a game in uncertain conditions with lack of opponents’ strategies.
Especially, in such games as two-person zero-sum games, the payoff value of each player’s strategy is imperfect, so high accuracy of player modeling cannot be guaranteed. In general, statistical method processes uncertainty mathematically with lots of observed numerical value data, but observed data usually contain occasional fluctuation caused instantly by various reasons as well as essential information about opponents.
Being used as a technology of several variables which identifies common characteristic factors in an invariable set, statistical factor analysis uses probability methods for factor analysis. However, these methods include invariable assumptions about probability distribution so the results may not always be right. Also, there are some cases where modeling is not suitable in practice. Though modeling is not correct strictly, we can draw nearly right conclusions from those hypotheses if it is approximately suitable.
Game theoretical decision adoption is a decision-making problem which determines how the best result can be obtained when the result depends both on its own and on the opponent’s actions.
Some decision-making problems like a zero-sum game are inflexible in target weight according to the structure, so they are changed and affected by opponents. Information analysis methods used in the past are not sufficient to deal with these problems.
Kim Ok, a researcher at the Faculty of Information Science and Technology, has proposed an algorithm where a player’s model can be estimated by a small amount of game data in a two-person zero-sum game characterized by a monotonically decreasing function.
The algorithm is based on the analysis of game process profiles. First, she introduced ordered weight operators to the strategic sequence determination of players and defined a compensation function considering monotonically decreasing character of a two-person zero-sum game. Then, she evaluated the game payoff value of the strategy and conducted player modeling.
The proposed algorithm will contribute to enhancing the accuracy of player modeling in two-person zero-sum games.
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Jo Nov 4, 2023
“Chronicles of the Feudal Joson Dynasty” is a “government journal” where the 500-odd-year history of the feudal Joson dynasty from 1392 to 1910 is recorded in order of year, month and date classified by the kings.
It is in 1 763 volumes and over 900 books.
“Chronicles of the Feudal Joson Dynasty” is classified by the kings into “Thaejo Sillok” (Chronicles of Thaejo), “Jongjong Sillok” (Chronicles of Jongjong), “Thaejong Sillok” (Chronicles of Thaejong), “Sejong Sillok” (Chronicles of Sejong), etc.
With huge amount and rich contents that could hardly be found in the world, “Chronicles of the Feudal Joson Dynasty” is a precious treasure of our nation.
During the hard-fought Fatherland Liberation War decisive of the destiny of the country, President
Under the wise leadership of the great leaders possessed of ardent love for the nation, all the contents were translated into Korean, thus widely used these days for historical studies.
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