Jo Jul 5, 2024
Flexibility is a key concept in the management of modern manufacturing systems. The principal motivation is to achieve rapid response to manager’s demands by improving the efficiency of a job-shop while retaining its flexibility. To achieve this goal, the term flexible manufacturing system (FMS) is defined. FMS is an integrated computer controlled complex of automated material handling devices and numerically controlled machine tools that can process medium-sized volumes of a variety of part types. Flexible manufacturing systems have many potential advantages including high flexibility and high machine utilization rate.
As scheduling is the core of this control system, it plays a decisive role in achieving a goal. FMS scheduling problems are more difficult than those of conventional production systems because of a number of reasons such as machine setup times, part routing and operations scheduling. Flexible manufacturing system scheduling problems are very difficult, so mathematical modeling methods need to be improved to solve them.
Pak Myong Chol, a researcher at the Robotics Institute, designed a scheduler based on a self-adaptive genetic algorithm and obtained the optimal solution for the job-shop schedule. Then, he constructed a flexible production simulation system with the scheduling module and Flexsim and conducted a simulation based on the optimized part scheduling.
The simulation results verified that it is possible to reduce the total machining completion time, increase machine utilization and realize process optimization.
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Jo Jul 3, 2024
Korean parents have a traditional custom of giving a special party to their children celebrating their first birthday.
Traditionally, rice cakes such as steamed rice cake, sorghum cake coated with red-bean jam and five-colored half-moon-shaped rice cake stuffed with beans and flavored with pine needles and fruits of the season including dates, apples, pears, persimmons, etc. were prepared on the table, and things like rice, thread, brush, book and bow were placed in front. Grown-ups, watching the baby’s cute tricks at the table, wished them normal growth, future happiness, great talents and good fortune.
Dishes prepared for first birthday were the same for both sexes, but objects were different.
For boys, a bow and arrow and a book and brush were prepared to the effect that parents wanted them to be a brave warrior or a scholar.
For girls, a reel of thread, a ruler, a pair of scissors, etc. were prepared. These show the desire of parents for their daughters to be good at needle work.
The custom of giving a first-birthday party reflects the love and desire of our people for their children to be excellent persons who defend the country and promote the happiness of their families.
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Jo Jul 2, 2024
ASPEN PLUS, a chemical process design system, is widely used for solving scientific and technological problems arising in the process, device design and process operation, for production of chemicals.
Process simulation techniques have been widely used in the development of new processes because of their high economic effectiveness and scientific accuracy. So far, many researchers have used ASPEN PLUS to simulate gasification processes.
Choe Hyon Il, a researcher at the Faculty of Metal Engineering, has developed an entrained-flow gasification compartment model, which consists of sub-models of pyrolysis, combustion and gasification, by combining the modules provided by Aspen Plus, and analyzed the effects of operating conditions, i.e., oxygen to coal ratio, steam to coal ratio and pressure, on the composition of coal gas.
The results are as follows.
As the oxygen to coal ratio increases from 0.7 to 0.9, the CO content increases by 16% in the outlet gas and the H2 content decreases by about 20%. The CO2 content starts to increase when the oxygen to coal ratio is greater than 0.85. When the steam to coal ratio varies from 0.12 to 0.6, the CO content in the outlet coal gas is reduced by 50% and the H2 content by 29%. As the pressure increases, the effective content in the outlet coal gas decreases, but it is not very large, and especially the effect becomes weaker above 300kPa.
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Jo Jul 1, 2024
Ryonggok School is located at the southern foot of Mt Ryongak in Pyongyang.
It was a private institution of the feudal Joson dynasty for educating rising generations.
The school was first built in 1656 and rebuilt in 1713, which is still preserved.
In line with the general requirements of private schools, it is divided into two zones ― lecture halls and temple.
If you go through the outer gate into the yard, you will find an eastern lecture hall on the right and a western lecture hall on the left. A flight of steps in the north of the yard leads up to the inner gate. If you walk through the inner gate, you will see a temple. To the northwest of the temple is a pavilion for a monument.
Ryonggok School, one of the typical private schools of the country, is a precious cultural legacy that shows the appearance and architecture of educational institutions in the years of the feudal Joson dynasty.
President
Thanks to the policy of the Workers’ Party of Korea on protecting national heritage, Ryonggok School is in good preservation and maintenance.
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Jo Jun 30, 2024
The transient electromagnetic method (TEM) is an efficient geophysical prospecting method widely used in mineral exploration, groundwater detection, etc.
When working by TEM, firstly, the transmitter injects the current into the transmitter loop, which will excite the primary magnetic field in the ground. When the transmitter current is abruptly turned off, then the receiver measures the changing rate of the secondary magnetic field using the receiver loop. Ideally, the primary field is therefore absent while measuring. The transmitter loop of TEM system has large inductance and small resistance. Its power supply utilizes rechargeable batteries and the H-bridge inverter is used to generate bipolar pulse current. In most TEM systems, the typical waveform of transmitter current is referred to as a bipolar square pulse. However, in practice, the real current waveform is often distorted and different from an ideal square pulse because of the dynamic characteristics resulting from the inductive load (the transmitter loop), the energy-storage components and the parasitic parameters of circuit elements. The waveform quality of the transmitter current affects the measuring accuracy.
Therefore, there has been a lot of research to further shorten the fall time of current pulse and improve the linearity of falling-edge.
Jang Chol Jin, a researcher at the Nano Physics Engineering Institute, has proposed a TEM transmitter topology using the passive voltage clamp circuit and the divided transmitter loop. The proposed scheme can greatly shorten the fall time of current pulse and improve the linearity of falling-edge, which is of great significance in mine TEM surveys or shallow TEM detections. Besides, it has simple circuit structure.
The details are found in his paper “Fast Turn-off of Pulse Current using the Clamping Circuit and Divided Loop in TEM Transmitter” in “Informatica” (SCI).
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Jo Jun 29, 2024
Accurate evaluation of ozone saturation property in bulk grains is very important for evaluating the effectiveness of ozone treatment on them.
Kim Su Gil, a researcher at the Nano Physics Engineering Institute, has proposed a model of ozone deposition during ozone treatment on bulk grains and evaluated ozone saturation property with the saturation time determined by the model.
First, he built a model of ozone deposition on bulk grains based on a material balance of ozone.
Second, he applied the model to calculate the time-dependent deposition velocities of ozone at various flow rates and depths in columns of wheat grains.
Third, he analyzed the saturation property of ozone in bulk grains based on the deposition velocities and compared it with previous works.
Finally, he determined the surface reaction probability of wheat grains.
You can find the details in his paper “Modeling ozone deposition on bulk grains and ozone deposition in columns of wheat grains” in “Journal of Stored Products Research” (SCI).
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