Jo Dec 23, 2022
Ozone is one of the strongest oxidizers and disinfectants, and it does not leave any residual toxin as it is decomposed into oxygen. That is why it has been widely used in domestic and industrial areas such as disinfection of drinking water and air, wastewater treatment, pulp bleaching, food processing, decolorization and deodorization.
A research team led by Kim Jong Guk, a researcher at the Nano Physics Engineering Institute, has developed enamel ozone tubes and different types of DBD ozone generators. The most effective and practical one of all ozone generation methods is dielectic barrier discharge (DBD), which generates non-thermal equilibrium plasma.
A DBD ozone generator consists of an ozone tube and high-frequency high-voltage power supply. The ozone tube has an enameled steel tube as an internal electrode and a stainless steel tube as an external electrode. It shows stronger resistance to thermal shock and better heat dissipation than glass or ceramic material.
Addition of nano-powders as mill additive increases adhesive strength, dielectric constant and dielectric strength, which ensures a long lifespan of the generator and produces high efficiency of ozone generation. Water cooling for internal and external electrodes effectively prevents temperature rise when the ozone tube discharges, thus ensuring safe operation and high ozone concentration output. By using high-frequency power supply and intelligent control system, ozone output can be changed on demand.
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Jo Dec 22, 2022
Apatite is an important mineral resource that plays an important role in many fields such as production of phosphoric acid and phosphate fertilizer.
Flotation technology is the most important method for beneficiation of apatite, and anionic fatty acid and their salt collectors are most-commonly used collectors in the direct flotation of phosphate ores.
Anionic fatty acid collectors have been proven both theoretically and in plant practice to be highly efficient in the flotation of apatite. Under basic conditions (pH10), fatty acid is saponified, which results in a negatively charged carboxylate ion. The negatively charged carboxylate ion then reacts with calcium on the apatite surface to form calcium carboxylate. This chemisorption method is generally considered to be the primary method of fatty acid adsorption onto the apatite surface in alkaline conditions.
Although a flotation mechanism of apatite using sodium oleate as a collector has been studied by several investigators, the flotation mechanism, reaction processes and associated surface reaction products still remain controversial.
Jong Kwang Sok, a researcher at the Faculty of Mining Engineering, synthesized a new collector for apatite flotation by a series of reactions including sulfation and amidation, using sodium oleate as raw material. Then, he carried out an investigation on the flotation behavior and mechanism of oleic acid amide onto apatite by micro flotation tests, zeta potential measurements, and XPS analysis.
The flotation results showed that mixing sodium oleate and oleic acid amide could float apatite well in a pH range of 7.5–9.5 even at the acid number of 120 mgKOH/g and it exhibited better collecting capacity on apatite than a sodium oleate collector. The XPS analysis data correlated with zeta potential showed that the zeta potential of apatite became more negatively charged at around pH8.5 and the oleic ions (C17H33COO−, (C17H33COO)22− and C17H33CONH−) in the mixing collector suspension could get chemisorbed by Ca-O bond formation on the apatite surface, and that the molecular (C17H33CONH2) and micelles ((C17H33CONH2)m) in oleic acid amide could get chemisorbed on the apatite surface by Ca-O or Ca-N bond formation.
You can find more information about this in his paper “Flotation mechanism of oleic acid amide on apatite” published in the SCI Journal “Colloids and Surfaces A: Physicochemical and Engineering Aspects”.
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Jo Dec 20, 2022
Kim Jang Hak, a section head at the Faculty of Distance Education, has proposed a new learning content model and a communication interface with interactivity and feedback structure considering the requirements and levels of learners while meeting the pedagogical requirements for distance education.
Generally, distance education system consists of three components, namely, learner, learning content and learning management system.
Learning-based interaction is mainly of three types, i.e. learner-content, content-management system and learner-management system.
Learning content consists of a content object and an interaction object with communication interface. The content object is Sharable Content Object (SCO) for teaching activities like lecture, experiment, practice, etc. The interface object is for interaction with learners through the communication interface and standardized communication with the management system.
If the structure of content is properly defined and standardized for interaction and feedback control, the reusability, extension and inter-operability of content can be ensured and it can be used in other management systems. The design of the content in hierarchical structure allows reuse of some of the content object in other contents.
On the basis of SCORM, the content model and learning object metadata are defined in the figure above. In the figure, “organization” is a learning unit and “item” is learning resources. “Resource” is a reference set, that is, SCO or asset of minimum unit. The root folder of the content has index.html, imsmanifest.xml, XSD and DTD, metadata.xml and resources. The content model is in imsmanifest.xml and metadata files.
Finally, he managed to form the content by adding communication interface with four control objects for interactivity and feedback control to the content model in hierarchical structure. The communication interface is made up of display control object, learning control object, communication control object and evaluation control object.
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Jo Dec 16, 2022
A research team led by Kim Tok Su, head of the Electric Power System Institute, and Mun Yong Guk, a section head at the same institute, has developed a flow meter which measures flow in real time in hydropower plants by using Winter Kennedy method.
Winter-Kennedy method utilizes a static pressure difference between the outside and the inside of a turbine spiral due to the centrifugal force acting on the curved streams of liquid in the spiral case.
The flow calculation formula in the flow meter using Winter Kennedy is Q=khn, where K is a constant coefficient and n is a power exponent which is theoretically equal to 0.5, but could be chosen between 0.48~0.51.
Generally, the values of the constant K can be determined experimentally by using flow Q measured by other standard flow meter. However, they have established a method of determining the coefficient K through FLUENT simulation.
They have introduced and examined the proposed flow meter in a generator. The result was n=0.497 9, K=0.057 and the maximum error compared with a standard flow meter was 0.616%.
As this simulation method is helpful to estimate power exponents and flow coefficients for any spiral cases, the flow meter can be used for all hydro power plants with a spiral case. It is simple in installation and it does not disturb fluid flow. Moreover, real-time measurement is possible with low cost but high accuracy.
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Jo Dec 15, 2022
Production systems operated in practice consist of repairable components and such systems may mostly be modeled as a direct-parallel system. Thus, analysis of the reliability characteristics of a direct-cold standby system is important in the reliability analysis of the system.
Most of the components for a repairable system are not the same after repair as new ones and component’s lifetime decreases with the increase in the time of use. What is more, the time for repair increases more and more once they stop working, which finally leads to complete failure.
On the assumption that the lifetime and repair time of components follow a geometric process, Kim Man Su, a lecturer at the Faculty of Applied Mathematics, has studied the reliability of several dual series direct-parallel systems in consideration of such decrepitude.
The figure above shows a state transition graph of a system, where a circle stands for in operation and a square means break down.
It is assumed that the system consists of components 1, 2 and 3, and components 2 and 3 make up a dual cold standby system, which is then connected with component 1 directly. Here, component 1 gets priority in repair. There is a repairman. Components 2 and 3 are repaired in order of failure.
The system is a unidirectional closed dual series cold standby system. It means if component 1 fails, the system breaks down.
At the beginning, three components are all new, and components 1 and 2 are in operation and component 3 is under cold standby. When the three components in the system are in good condition, two are in operation and one is under cold standby. The repairman sets to work once one of them fails. At the same time, the standby one begins to work. When the failed one has been repaired, it is put on cold standby until the next failure. If one fails while the other is still under repair, it must wait for repair and the system breaks down. It is assumed that each component after repair is not ‘as good as a new one’.
A deteriorative repairable system will not support constant repair of its components. For a deteriorative repairable system, it seems more reasonable to assume that the successive working time of the system after repair will become shorter and shorter while the consecutive repair time of the system after failure will get longer and longer. Ultimately, it cannot work any longer, nor can it be repaired.
In a dual series cold standby system, after N cycle of component 2, when it finishes working, a plan to replace it with a new one (the same as the first dual series cold standby system) is called N replacement policy.
If the lifetime and repair time of components follow a geometric process in a unidirectional closed dual series cold standby system, the solution of state probability (density) is difficult to present analytically, so replacement cycle N needs to be defined and the characteristics of the system be analyzed.
In order to determine an effective replacement cycle, he studied the stationary conditions of the unidirectional closed system using the transitive property of the Markov chain assuming every state in all possible cases in the system.
The results showed that the proposed mathematical method could be effectively used in different pieces of research of other kinds of queuing models.
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Jo Dec 8, 2022
Humidity is an important physical quantity in all fields of human life. In recent years, fiber-optic humidity sensors with compact size, high sensitivity and good resistance to chemical corrosion and insusceptibility to electromagnetic interference have been widely studied.
Yu Hyong Su, a researcher at the Semiconductor Institute, has proposed a novel optical humidity sensor which is simple in structure, easy to make and cost-effective with high sensitivity, a wide range of operation, and good safety and reproductivity. It consists of light source, a gap and an acrylic resin film coated on PSD.
Experimental results verified very satisfactory performance of the humidity sensor in terms of its sensitivity, hysteresis, linear response to the humidity and long-term stability.
You can find more information about it in his paper “Widely sensitive optical humidity module by using acrylic resin and a position sensitivity detector” published in the SCI Journal “Optical and Quantum Electronics”.
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