Jo Sep 8, 2026
Running accuracy and stiffness of spindle units in a machine tool have a crucial influence on the accuracy and reliability of the whole machine. Fatigue life calculation of bearings in spindle units is important to ensure the good performance of spindle units and to design machine tools scientifically.
In order to predict the fatigue life of rolling bearings used in machine tools, the stresses generated at the contact surface of interface are needed. This stress distribution is mainly determined by the pressure acting on the contact surface. Accurate calculation of pressure distribution can be done by FEM, which considers not only the generator shape but also the length in the contact state. The calculation of pressure distribution requires great computational efforts, which is more important in the case of repeating the calculation of many contacts in complex rolling pairs than in the case of simple contacts.
In the previous studies, several methods were used for the fatigue life of bearings, but they failed to analyze the effect of the roll profile and ring misalignment on the bearing fatigue life in a direct way.
Having developed a mathematical model for the fatigue life calculation of cylindrical roller bearings widely used in machine tool spindles, Kim Myong Il, a researcher at the Faculty of Mechanical Science and Technology, proposed a reasonable roller profile by calculating the fatigue life of bearings of three roller profiles and comparing them by FEM.
The results showed that the stress distribution is significantly lower for circular or logarithmic correction than for rectilinear roller generators, but the stress distribution is higher for circular correction, and the overall logarithmic correction significantly improves the fatigue life by 4.5 times.
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Jo Sep 7, 2026
High-grade copper-bearing ores have been increasingly depleted and instead, low-grade and complex ores have now become dominant in copper production. The existing production process for low-grade copper molybdenum ore has the disadvantage of high cost and high energy consumption. Therefore, a great deal of attention is being paid to the simple and environmentally-friendly bioleaching. Without proper heap bioleaching technology, millions of tonnes of low-grade copper ore might be left as waste.
While many studies have been carried out on the bioleaching of chalcopyrite, which is the main copper-bearing material, few studies have been reported on the direct bioleaching of complex minerals containing chalcopyrite.
Cha Kwang Chon, a post-graduate student at the Faculty of Mining Engineering, investigated the feasibility of bioleaching for copper recovery from low-grade, complex chalcopyrite in a column reactor.
The ore mainly contains pyrite and chalcopyrite as sulphide minerals and quartz as the main gangue minerals.
He carried out the tests in a column reactor using a mixture of inoculums used for bioleaching of pyrite.
The results showed that the dissolution of copper reached 85% after 120 days at 35-45℃.
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Jo Sep 6, 2026
The Taedong Gate is the eastern gate of the Walled City of Pyongyang of Koguryo Kingdom (277 BC-668 AD) on the banks of the Taedong River in Taedongmun-dong in Central District of Pyongyang.
It was originally built as the eastern gate of the keep of the Walled City of Pyongyang, the capital of Koguryo, in the mid-6th century, and was rebuilt in 947 and 1392, the initial periods of the Koryo dynasty and the feudal Joson dynasty. The present structure was built in 1635.
It was the most important and biggest one among six gates of Pyongyang. It is 19 metres high. The embankment is 26.3 metres long, 14.25 metres wide and 6.5 metres high. In the middle of the embankment is an arch-shaped gateway whose four corners gradually widen outwards on the plane surface so that it can bear the weight of the structure.
The gate is considered as a typical example of gate construction of the feudal Joson dynasty embodying magnificence, beauty and airiness, as it has the architectural style and structural features of the early period of the feudal Joson dynasty, which inherited and developed the architectural art of Koryo.
Today, the gate serves as a recreational ground for the working people, youth and schoolchildren as it goes well with the Pyongyang Bell House, Ryongwang Pavilion and the Taedong River promenade’s flower bed facilities while boasting the long history of Pyongyang, which turned into a magnificent modern capital city.
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Jo Sep 4, 2026
The water electrolysis technology using proton exchange membranes (PEM) has now become more widespread in its use due to its simple operation and maintenance and high productivity per unit volume as an intensive and high-efficiency water electrolysis technology that can directly produce high-purity, high-pressure hydrogen without special ancillary devices. Despite these advantages over alkali water electrolysis technology, which is widely industrialized across the world now, its disadvantage is high cost. It is attributable to the high cost of proton exchange membranes and electrode catalysts for them.
Ho Kuk Chol, a post-graduate student at the Institute of Nano Science and Technology, prepared ATO-supported IrO2-RuO2 composite catalysts as anodic catalysts in PEMWE by using the Adams method and investigated their electrochemical and water electrolytic properties.
When the Ir content was 30% for the IrO2-RuO2 composite catalyst and 80% for the supported catalyst, the catalysts had current density of 77.5mA/cm2 at the voltage of 1.5V in 0.5mol/L H2SO4 solution. The stability experiments in the same solution showed that the supported composite catalyst had almost the same stability as IrO2. It was concluded that the prepared catalyst showed almost the same performance with 60% reduction in cost compared to IrO2 catalysts.
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Jo Sep 3, 2026
In September there are seasonal subdivisions of Paengno and Chubun.
Paengno means the time when clear dew falls with a sign of autumn. Chubun means that summer completely gives way to autumn. On the day of Chubun the length of day and night is almost the same and afterwards days gradually get shorter than nights.
This year’s Paengno and Chubun fall on September 7 and September 23 respectively.
From olden times, the Korean people gathered foxtail millet and other crops and sowed wheat and barley and they picked cotton in some regions in that period.
Medicinal herbs and wild fruits were gathered in mountainous regions.
Around Chubun, rice was harvested in paddy fields, soybean and other crops were gathered from dry fields and wheat and barley were planted in real earnest.
September 25 this year is Chusok (Harvest Moon Day), one of the greatest folk holidays of the Korean people.
Chusok means autumn evening and the Korean people enjoyed the folk holiday viewing the full moon in autumn when all kinds of cereals ripen. On the holiday, they first visited their forefathers’ graves to cut grass of them and hold memorial services arranging offerings made of new crops of the year. This was a reflection of the ennobling good manners and customs of the Korean people who always respect seniors and are polite and faithful to duty.
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Jo Aug 28, 2026
UN and many countries are calling for urgent measures because air pollution caused by air pollutants seriously threatens human health and causes premature death. Many investigations and studies have revealed that PM2.5 is a main pollutant that destroys the environment of ecosystems and harms human health, and that air pollutants containing PM 2.5 cause various diseases such as respiratory, lung and heart diseases.
In the air pollution concentration prediction task, it was reported that the artificial neural network (ANN) model improves prediction performance while avoiding the complexity and annoyance of modeling, compared to the deterministic method which has lack in representing the heterogeneity and nonlinearity of many factors related to pollutant formation.
Therefore, many researchers have begun to apply artificial neural networks extensively to air pollution prediction, and since then they have ensured the accurate prediction performance by combining deep neural networks with several other optimization techniques that have shown dramatic effectiveness in the prediction of large time series data. In a word, their research results show that deep learning models significantly improve their performance when combined with several other effective analytical methods on time series data rather than being used as a single model.
Based on this analysis, Pak Un Jin, a researcher at the Faculty of Automatics, proposed a hybrid model consisting of convolutional neural network (CNN)-long short-term (LSTM) with multifractal detrended fluctuation analysis (MF-DFA) for air pollution and meteorological time series data, and used it to predict the next day’s 24-h average PM2.5 concentration in Beijing City.
The comparison of the performance indexes of the proposed model with MLP and LSTM models showed that the proposed model provides higher prediction accuracy.
For further details, please refer to his paper “A deep learning approach via multifractal detrended fluctuation analysis for PM2.5 prediction” in “Journal of Atmospheric and Solar-Terrestrial Physics” (SCI).
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