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 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 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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Jo Jun 25, 2024
The genus Sinamia currently comprises about 8 species, all recorded in China.
Sinamia zdanskyi was first described by Stensiö, and subsequently, a great number of Sinamia were found in Gansu, Shannxi, Ningxia and Inner Mongolia around the Ordos Plateau.
A new specimen of Sinamiidae was collected from the Upper Cretaceous Seson Formation, the Democratic People’s Republic of Korea. It is similar to Sinamia liaoningensis in the shape of the more arched preopercle, relatively smaller size of the infraorbitals, more caudal fin rays, more scale rows between the origin of the anal fin and the dorsal margin of the body, and lack of serrated scales.
This discovery not only extends the geographic distribution of sinamiids, but also fills a blank in the sinamiid study in the DPRK.
You can find more information in the essay by Kim Pyong Song, an institute head at the Faculty of Earth Science and Technology, “First Occurrence of Sinamia (Amiiformes, Sinamiidae) from the Upper Cretaceous Seson Formation, Democratic People’s Republic of Korea” in “Cretaceous Research” (SCI).
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Jo Jun 23, 2024
All the digital data stored, copied and distributed on the network have their own unique information, and especially, digital images, as one of the fastest multimedia formats that can deliver their information in visual way, have a lot of information.
Most of the digital images transmitted through the network are private and, especially, digital images with sensitive information, such as medical diagnostic images, can lead to irrevocable disaster when they are disclosed to be abused. Therefore, it is very important for digital images to be digitally secured.
In general, digital images, when compared to text data, have characteristics of very large capacity, high overlap and strong correlation between adjacent pixels. In the meanwhile, digital image data require strong real-time property in communication, storage and distribution. Hence, it requires fast and secure image encryption algorithms. From this necessity, many previous researchers have proposed improved chaotic maps and applied them to various image encryption algorithms.
Chaotic map is generally classified into one-dimensional and high-dimensional ones. The former has advantages of simple structure, easy hardware and software implementation and low computational cost, while it has disadvantages of narrow chaotic behavior and non-uniform distribution of output chaotic sequences. The latter is difficult to implement in hardware and software due to its complex structure and multi-control parameters, and it also has computational complexity. In recent years, one-dimensional or multidimensional chaotic maps with good chaotic characteristics are proposed by combining the existing 1D chaotic maps that are fast and easy to implement in software and hardware.
Based on the analysis of the prior works, Pak Chan Il, a section head at the IT Institute, has designed a two-dimensional chaotic map with better chaotic performance than the prior ones and built a simple and fast pixel-level image encryption algorithm.
To start with, he configured a new 2D-ICCM (2D Infinite Collapse Coupling Map) with better chaotic performance by combining two 1D infinite collapse maps which have the best chaotic characteristics of all previous 1D chaotic maps. He confirmed through various experiments that the proposed 2D-ICCM has better chaotic performance than previous 2D chaotic maps.
Next, he proposed a new pixel-level image encryption algorithm which combined simple-structured pixel-level permutation and diffusion, and tested the performance by applying the proposed 2D-ICCM. The simulation and experimental results showed that the proposed image encryption scheme has excellent performance against various cyberattacks.
If further information is needed, please refer to his paper “A new image encryption algorithm using 2D infinite collapse coupling map” in “Multimedia Tools and Applications” (SCI).
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