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.

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℃.

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.