Jo Nov 17, 2023
Practical application of manipulators needs determination of their dynamic errors to guarantee positioning accuracy.
Many researchers determined kinematic errors of Delta parallel manipulators, but not dynamic errors.
Pang Thae Jin, a researcher at the Robotics Institute, has established a new method for dynamic error determination of a Delta parallel manipulator with three actuators using a deformation model.
He wrote an algorithm based on the kinematic and dynamic models and developed a program for obtaining dynamic errors of a Delta parallel robot, using MATLAB software.
His method can be applied to construction of control systems for error compensation of complicated manipulators of different shapes.
Jo Nov 15, 2023
Among the valuable cultural legacies created by our nation is Sungryong Hall in Central District, Pyongyang City.
Sungryong Hall is a shrine first built in the fifteenth century during the feudal Joson dynasty. It was originally used for a memorial service for King Tangun, the founder of Ancient Joson, which was the first ancient state in our country’s history. Later, memorial services for King Tongmyong were also held here. The present building was rebuilt in the eighteenth century.
The original hall was made up of a main hall, two-kan servant’s quarters to the east and west with two one-kan doors each and a three-kan gate. Most of them were destroyed by the Japanese imperialist aggressors, with only the main hall and the gate survived. During the Fatherland Liberation War, they were badly damaged by the US imperialists’ barbarous bombing raids. Sungryong Hall is now restored to its original state. It is a valuable architectural legacy reflecting the architecture of the days of feudal Joson dynasty.
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.
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.
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.
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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