Jo Mar 12, 2025
At present, fabrication of micro-scale components and devices is one of the major technologies with considerable potential, and it is of great importance to make manufacturing processes suitable for their medium and large-scale production.
In the last decade, there has been an increasing demand for micro-sized components and their microstructures, which has led to the introduction of micro-injection molding technology to fluid control techniques and medical tools. The most promising process of this technology is micro powder injection molding (μPIM), a product manufacturing technology for producing small size components of complex shapes in large quantities.
However, the μPIM process suffers from several difficulties, unlike the PIM process. In the μPIM process, there is a high demand for powder. For example, the fluidity of raw material depends on the type and size distribution of powder, and the size change after debinding depends on the friction force between particles. In addition, the lubricity of the binder depends on the particle surface conditions, and the debinding rate also depends on the particle morphology, particle size, etc. Raw material powder should be less than 5㎛ in size. The composition of the binder used for mixing raw materials has a great influence on the product's molding and demolding. That is, it needs to have high viscosity. The temperature should be well controlled at the time of debinding of various mixed binders to eliminate cracking during sintering of products and to ensure dimensional accuracy after sintering.
Ri Un Sim, a researcher at the Faculty of Materials Science and Technology, while preparing a 800㎛ micro-gear from 1Cr18Ni9 stainless steel spray powder using μPIM technique, has analyzed the effects of injection temperature, injection pressure and injection speed on the formation of components.
As a result, she has found that injection molding is best at the injection temperature of 130℃, scanning pressure of 70㎫ and scanning rate of 60mm/s.
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Jo Mar 11, 2025
In recent years, it has become a pressing issue in practice to modernize the fish quick-freezing process and increase its productivity in keeping with the huge increase in the catch. The main objective of increasing the amount of quick-freezing production is to automate, streamline and control the quick-freezing process on a high level, along with the use of high-performance quick-freezing equipment. For this purpose, it is necessary to determine appropriate design parameters of a lifting up-down machine (LUDM) for quick-freezing.
So far, there have been many studies on LUDM. At present, machines for transshipping mushroom substrate cases are in use in mushroom farms and LUDMs are used for tiles and roofing tiles in the building materials industry. LUDM for fish quick-freezing has two guide pillars, which involves tipping risk during operation.
Pak Myong Nam, a researcher at the Robotics Institute, has modeled LUDM for fish quick-freezing on SolidWorks, carried out a stability analysis by ADAMS, and determined the design parameters by the quality engineering technique.
Thus, he ensured high accuracy and automation of LUDM, which improved the quality and hygienic safety of fish quick-freezing, saved a lot of labor and realized the automation of the overall fish quick-freezing process.
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Jo Mar 9, 2025
In enhancing the role of the logistics enterprises, evaluation of the ability of enterprises in a scientific and effective way is of great importance. Accurate assessment of the ability of logistics enterprises can help to find the right way to ensure their development.
There are several methods for logistics performance measurement including AHP (analytic hierarchy process), multivariate statistical analysis (principal component analysis, factor analysis, etc.), etc., which have their own advantages and disadvantages for their application.
Fuzzy comprehensive evaluation is a comprehensive evaluation method that applies fuzzy mathematical methods when fuzziness is involved in the process of comprehensive evaluation of objects, and thus it is regarded as a practical analytical method for evaluating the capabilities of logistics enterprises.
Song Kwang Hyok, a section head at the Faculty of Management of Industrial Economy, has set the weight of indexes like management level, technical strength, transport capacity, informatization level, competitive power and customer service capacity by AHP, and proposed a method of evaluating the capacity of logistics enterprises by fuzzy comprehensive evaluation using M (1, 2, 3).
The proposed approach allows enterprises to understand their own capabilities and to take necessary measures to improve their business performance.
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Jo Mar 8, 2025
There are two small pools called Ryonju Pools in Okryu Valley in the section of Kuryong Pool of Outer Kumgang of Mt. Kumgang, a noted mountain of the DPRK. There is a high cliff in the north of the pools and 400 meters away to the southwest of them is Kuryong Pool.
Ryonju Pools are two ponds formed by the abrasion of glacier and water flowing down the valley for a long period of time.
The upper pond is small and the lower one is big.
The upper one is ten meters long, five to six meters wide and six meters deep while the lower one is twenty meters long, eight to nine meters wide and nine meters deep.
The waterfall between the two ponds is three to four meters high.
Ryonju Pools make Okryu Valley particularly attractive.
The pools have the name Ryonju as they are adjacent to each other like two threaded blue beads.
Ryonju Pools blend perfectly with the geographical features of the surrounding mountains, adding beauty to the mountainscape.
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Jo Mar 7, 2025
Recently, there have been many studies on the wide use of MOS-FET pH sensors modified with functionalized carbon nanotubes. However, no comprehensive and detailed study on the OH and N functionalization and pH sensing properties of multi-walled carbon nanotubes (MWCNT) has been found in the literature.
Pak Il Man, a section head at the General Assay Office, has studied the OH and N functionalization of MWCNTs and investigated their pH-sensing properties by modifying functionalized carbon nanotubes onto MOS-FETs.
First, he boiled MWCNTs in 63% HNO3 (analytically pure) at 120℃ for 40h, and filtered and washed them with deionized water to perform OH functionalization. Then, he carried out treatments by boiling them in 20% liquid ammonia and 0.1% gelatin solution, respectively, and by applying ultrasonic dispersion to the samples boiled in gelatin solution and conducting ultrasonic dispersion in 0.1% gelatin solution, respectively, to investigate the N functionalization properties.
He investigated the pH characteristics by modifying the MOS-FET drain with functionalized carbon nanotubes, and found that the pH-sensitive linear range of MOS-FET modified with N-functionalized carbon nanotubes was longer than that of MOS-FET modified with OH-functionalized carbon nanotubes.
As the pH sensor based on this is a strike and temperature resistant integral solid, it is possible to measure pH accurately in a coarse suspension that is stirred in a closed container or in a high temperature solution.
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Jo Mar 6, 2025
Zeolites have been widely used in various industrial fields including the chemical industry due to their unique catalytic properties and excellent adsorption and ion exchange capabilities, and there is a constant interest in developing zeolites with different performances, reducing their production costs and making their synthesis easier.
ZSM-5 zeolite, synthesized in the early 1970s, has a large specific area and high thermal and mechanic stability, and it has a porous structure consisting of alternating three-dimensional straight pore channels and Z-type pore channels, which makes it widely used in various fields, such as the industry of fine chemicals, oil chemistry, environmental protection, etc. Especially, it has been used as a catalyst, a molecular sieve and an adsorbent in the chemical industry.
ZSM-5 zeolite is usually synthesized by hydrothermal synthesis using silica raw materials, alumina raw materials and organic templates as synthetic materials. Aluminum sulfate, aluminum nitrate and sodium aluminate are widely used as raw materials of alumina source for ZSM-5 zeolite synthesis, while silica sol, water glass, etc. are widely used as silica source. In addition, quaternary ammonium salts, alcohols, amines and amino alcohols are used as organic templates. The choice of an organic template will determine the cost of ZSM-5 zeolite, which limits the industrial production of ZSM-5 zeolite.
Sin Hyok, a researcher at the Faculty of Chemical Engineering, has proposed a method of synthesizing ZSM-5 zeolite using water glass, aluminum sulfate and triethylamine as a silica source, an alumina source and a template, respectively, and determined the optimum crystallization condition for synthesizing ZSM-5 zeolite using such materials as mentioned above.
He defined the molar ratio of raw materials in aluminosilicate gel as 6Na2O:50SiO2:1Al2O3:1 300H2O:10C6H15N and performed hydrothermal crystallization at 100-150℃ for 30-42 hours. Then, he determined the optimum crystallization temperature and time, with relative crystallinity of 95% and solid product yield of more than 0.9.
He found that in a certain temperature range, the relative crystallinity and solid product yield increased with increasing crystallization time.
The proposed method is a new approach to prepare ZSM-5 zeolite from commercially accessible and relatively inexpensive raw materials.
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