Jo Mar 17, 2023
Measurement of low concentration oxygen gas is very important in chemical processes where several kinds of material gas and fuel gas are used. If the concentration of combustible oxygen gas gets high, it might cause explosion, which will have vicious influence upon the whole process. So, real-time measurement of oxygen at low concentration is essential for taking proper measures.
Two common techniques for sensing oxygen at low concentration are luminescent optical sensing and electrochemical sensing. Both demonstrate high sensitivity to low concentration oxygen. Fluorescent oxygen sensing has seen widespread adoption thanks to its inherent stability. However, application of this technique is limited due to complicated fabrication and short life time. On the other hand, electrochemical sensors are widely used and available in different forms according to the demands of users.
A research team led by Choe Chol Man, an institute head at the Faculty of Electronics, made an amperometric oxygen sensor based on the electrochemical method to manufacture an oxygen concentration measuring instrument, and introduced a refrigerator and a gas cleaning instrument for removing the effect of interference elements, thus completing a system of measuring low concentration oxygen gas.
The left picture shows the construction of the oxygen sensor incorporating a cathode, an anode, an electrolyte solution and a gas permeable membrane, all of which affect the characteristics of the sensor. They used silver with good oxygen reduction characteristics as a cathode, and silver/silver chloride electrode as an anode. KCl saturation solution and PTFE thin film were selected as an electrolyte and a gas permeable membrane, respectively.
They introduced digital signal processing technology to remove atmospheric noises so that the instrument could work properly in any operation environment, thus ensuring the stability and reliability of the instrument. The right picture shows the installation of the system.
The specification of the system is as follows.
Measurable band: 0~10%
Response time: 30s
Accuracy: 0.1%
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Jo Mar 14, 2023
A research team led by Kim Thae Ung, a section head at the Faculty of Automation Engineering, has established an integrated automation system of the ore dressing process for the production of apatite concentrate.
The system supports comprehensive monitoring and operation of a whole process by displaying process data including the information of operation state of motors in crushing processes, grinding processes and flotation processes, pulp density, flotation temperature, pH value, amount of reagent consumption and level of industrial water numerically and graphically. It saves data of process variables of the subprocesses in the corresponding data base.
The process interface consists of process monitoring, grinding process, flotation process, reagent supplier, operation mode and process history.
The system shows several advantages. The ore dressing recovery and the concentrate grade are guaranteed at over 80% and 30% respectively. The reagent consumption is reduced by more than 10% and the labor is economized by 15%.
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Jo Mar 10, 2023
Jang Rim Chol, a researcher at the Faculty of Mechanical Science and Technology, has developed a CNC engraving machine for cutting an EPS model.
The machine ensures high geometric accuracy and surface finish in cutting EPS models for lost form casting.
It consists of a computer, a control device, a mechanical system, an exhaust fan, etc.
What is new about it is the development of a spindle unit for EPS cutting and a rolling guide using ball bearings. Also, it has a rotary table that can change its rotating axis vertically and horizontally, so the machine offers satisfactory cutting of the EPS model of a spur gear whose diameter is 2 meters. The machine is also applicable to complex and large EPS models such as large bevel gears, housings and manikins.
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Jo Feb 28, 2023
Fast constructions from the Brownian motion and Brownian bridge are required in many applications such as Quasi-Monte Carlo simulations and statistical inferences on stochastic processes. A simple method for construction of discrete Brownian motion is a step-by-step method of computing the cumulative sum of i.i.d. normal variables.
The construction of N dimensional discrete Brownian motion (or a N-1 dimensional discrete Brownian bridge) that requires at most O(NlogN) floating point operations (flops) is called fast construction. Discrete Brownian motion can also be constructed using decompositions of its covariance matrix, and the method based on eigenvalue decomposition not only shows superior performances in many simulations over the step-by-step method but also becomes a fast construction. Usually the discrete Brownian bridge can be constructed from the discrete Brownian motion using the linear relationship between them. The inserting method using a decomposition of covariance matrix of discrete Brownian bridge gives another decomposition of covariance matrix for high dimensional discrete Brownian motion and it is very significant in Quasi-Monte Carlo simulations for financial derivatives.
Ri Sung Hyon, a section head at the Faculty of Applied Mathematics, has obtained eigenvalue decomposition of covariance matrix for discrete Brownian bridge and LDU (Lower-Diagonal-Upper) decompositions for covariance matrices of discrete Brownian motion and bridge newly and then proposed new fast construction methods on the basis of them. He has also proposed an inserting method for construction of discrete Brownian motion using eigenvalue decompositions which requires O(Nlog(logN)) flops.
The proposed new construction methods might be used effectively in simulations using Brownian motion and Brownian bridge. In addition, the construction algorithms would be used in analytical study for Brownian motion and Brownian bridge.
You can find more information about this in his paper “Decompositions of the Covariance Matrix of the Discrete Brownian Bridge: New Fast Constructions of Discrete Brownian Motions and Brownian Bridges” published in “American Journal of Applied Mathematics”.
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Jo Feb 27, 2023
One of the important problems for structure calculation of a tunnel is to estimate the stability of rock mass surrounding the tunnel.
A safety factor of rock mass surrounding the tunnel can be determined by strength reduction method (SRM). Here, the most important is to solve the criterion of critical state.
Recently, several researchers have conducted studies to apply SRM, which has already been in use for estimation of slope stability, in order to estimate the stability of rock mass surrounding the tunnel. Many researchers have compared the various criteria of the critical state of a slope, which is the most important in the estimation of slope stability by SRM. Although various criteria were developed, there were mainly 3 methods: penetration of equivalent plastic strain, non-convergence of numerical calculation and sudden change of horizontal displacement at a specific point.
Jong Tok Yong, a section head at the Faculty of Earth Science and Technology, has proposed a new method for determination of a safety factor by sudden change of equivalent plastic strain in the relationship between a reduction coefficient of strength parameter and equivalent plastic strain.
This method is based on elasto-plastic FEM and SRM by ABAQUS and Mohr-Coulomb yield criterion.
Simulations in circular and square tunnels showed how a safety factor varies with geometries, friction angles and cohesions and how it varies with quality change of rock mass, pore water pressure and tunnel depth.
If further information is needed, please refer to “Determination of safety factor for rock mass surrounding tunnel by sudden change of equivalent plastic strain in strength reduction method” published in the EI Journal “Geotechnology and Geological Engineering”.
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Jo Feb 26, 2023
Forward voltage drop of fast p+nn+ structure is affected strongly by the high-level carrier lifetime, reverse recovery time current by the low-level carrier lifetime, and reverse current by the space-charge generation lifetime. These 3 carrier lifetimes influence 3 main parameters of p+nn+ structure differently. When the low-level carrier lifetime is decreased in order to decrease the reverse recovery time, the forward voltage drop increases, and when the high-level carrier lifetime is increased for reducing the forward voltage drop, the reverse recovery time increases.
It is unknown how to adjust rationally the 3 main parameters of fast p+nn+ structure － forward voltage drop, reverse recovery time and reverse current.
In order to control these conflicting relations, Pak Pyong Su, a section head at the Semiconductor Institute, has illuminated the recombination center level formed on the basic floor of p+nn+ structure. Then, to determine the recombination center level coincided with the practical recombination center level, he has suggested an analytic method of determining the recombination center level formed by 2 carrier lifetime regulation sources.
First, he suggested main relative equations to determine the optimal recombination center level with numerical solutions. Second, he found the practical recombination center level which is irrelevant to the doping agent concentration and working temperature. Finally, he proposed an analytic method to determine the co-additive recombination center level coincident with the practical recombination center level by adding any 2 types of carrier lifetime regulation sources.
To illustrate the effectiveness, he used an analytic method to calculate the recombination center level formed in the silicon semiconductor material with addition of gold and iridium at the same time.
The proposed method demonstrates that it is effective in the determination of the co-additive recombination center level when any 2 carrier lifetime control sources are added and that it can be applied to the rational regulation of the 3 parameters of a fast diode in the random doping agent kinds and co-additive concentration and the other intervals of working temperature.
The details of this are found in his paper “Analysis of the optimal recombination center level to adjust rationally the 3 main parameters of p+nn+ structure” in the EI Journal “Journal of Power Electronics and Devices”.
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