Jo Feb 18, 2025
Chlorine is widely used in industry as a strong oxidizing agent. One of its most important features is that it can be used as a disinfectant in water treatment and purification. When it is used for disinfection, disinfection gets faster due to the rapid attack to microorganisms by its active chlorine species. Such chlorine is generated during the reaction of chlorine ion with ozone at the time of ozone disinfection of seawater.
Recently, ozone has often been used for water disinfection in swimming pools and aquariums that use seawater. When seawater undergoes ozone disinfection, ozone as a stronger oxidizing agent oxidizes chlorine ion in the seawater, thus generating free chlorine. However, too much consumption of ozone results in the higher amount of free chlorine, which is harmful to the fish and the human body.
The amount of free chlorine in various kinds of aqueous solutions can be determined by several methods including titration, spectrophotometry and electrochemical analysis. The quantification of free chlorine by electrochemical analysis is accepted as an economical and reliable method with high selectivity since it employs oxidation and reduction properties of free chlorine.
It is an innovative analysis that determines the amount of free chlorine by using the oxidation peak of the hydrogen generated by water analysis during the cyclic voltammetry (CV) with a bare platinum electrode with no addition of any supporting electrolyte to the seawater.
However, since the peak potential of the oxidation peak of the hydrogen generated through water electrolysis in CV of seawater using a bare platinum electrode ranges from -0.8 V to -0.9 V, it could be overlapped with the peaks of some components essentially coexisting in the sample. Furthermore, as platinum has excellent electrochemical characteristics, it has a defect of exhibiting the low selectivity for indirect determination of free chlorine.
Ko Kye Hak, a researcher at the Faculty of Chemical Engineering, has proposed a new possibility of indirect determination of free chlorine using a graphite-epoxy composite (GEC) electrode instead of Pt disk electrode by interpreting the relationship between the peak current of the oxidation peak for hydrogen generated through water electrolysis in CV and the amount of free chlorine.
According to the quantitative analysis, the sensitivity for the GEC electrode is one third of that for the bare platinum disk electrode, but better results can be obtained without any effect of interferences.
You can find more information in his paper “Indirect determination of free chlorine in seawater by cyclic voltammetry using graphite-epoxy composite electrode: Hydrogen adsorption capacity of graphite-epoxy composite is one-third of that of platinum” in “Sensing and Bio-Sensing Research” (SCI).
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Jo Feb 17, 2025
A frequent problem in the field of image processing nowadays is to obtain images close to ideal images from noisy ones.
In particular, the inefficiency of detectors in the field of diagnosis based on images has made this problem even more serious. The most common feature of noise in medical images is two: the probability distribution is iterative, and the noise is non-linearly changed through the reconstruction process, resulting in a lower resolution of the resulting image data.
The edge-preserving filter does not degrade the image resolution as it does not smooth the image data, but removes noise by suppressing only noise signals. Therefore, it is widely used in image diagnosis with high accuracy for tumors or patient organs. In these applications, filters that smooth the boundaries and displacements lose diagnostic significance because they increase the ambiguity between the critical parts of diagnostic significance and reduce the accuracy of images.
There are two problems with using a boundary-preserving filter.
First, almost all edge-preserving filters can be applied only to typical Gaussian noise filters. Therefore, these types of filters cannot be applied to image data such as low-dose CT image noise. Because the pixel values in these images follow the Poisson distribution, noise variance is not the same throughout the image.
Second, when using these types of filters, certain information about the noise variance at any location should be available for local or global parts of the image.
On the basis of the analysis of the path characteristics rather than noise, Ri Hwi Song, a researcher at the Faculty of Biology and Medicine Engineering, has proposed a sinogram estimation method based on various optimization methods and a corresponding algorithm to recover the ideal image by maximally preserving information only in the sinogram data distorted by various factors and removing noise.
First, he analyzed the path characteristics of the sinograms in low-dose CT images and used optimization methods to optimize the information content of the sinograms in low-dose CT images. On this basis, he proposed a method to remove the noise components and a corresponding algorithm for their implementation. Then, he analyzed the results of sinogram refinement using the optimization method, comparing the image obtained through image reconstruction with the ideal CT image data, and proposed some methodologies to speed up the algorithm.
Qualitative analysis of this image quality improvement method shows that the sinogram estimation algorithm for low-dose CT using the optimization method can effectively remove noise while preserving both image structure and boundary even in the presence of large noise and non-stationary noise as in low-dose CT. He has also confirmed that decreasing the operation time of the sinogram estimation algorithm using the optimization method could lead to the possibility of drastically decreasing the dose in CT.
You can find the details in his paper “Sinogram restoration based on shape property in computed tomography” in “Informatics in Medicine Unlocked” (SCI).
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Jo Feb 16, 2025
Due to their remarkable characteristics, laminated composite shells and plates are commonly found in various engineering fields such as mechanical, civil, aerospace, marine, and automotive applications. Composite shells and plates of varying thickness are widely used in different industries due to their light weight and compact design.
Recent studies have focused on the dynamic characteristics of these materials, and meshfree methods have attracted significant attention from researchers.
Kwak Song Hun, a researcher at the Faculty of Mechanical Science and Technology, has proposed a meshfree Jacobi point interpolation (MJPI) approach for the dynamic analysis of sandwich laminated conical and cylindrical shells with varying thickness.
First, he established theoretical formulations for sandwich laminated shells with varying thickness using the modified variational principle within the framework of first-order shear deformation theory (FSDT). Then, he expanded the displacement components of the sandwich shell using the MJPI shape function and Fourier series in the meridional and circumferential directions, respectively.
He verified the accuracy and reliability of the proposed MJPI shape function through the comparison with the numerical results from published literature and the commercial simulation tool Abaqus. Finally, he investigated the effects of different parameters such as thickness gradient, thickness power index and boundary condition on the free vibration and dynamic response of the sandwich laminated shell.
For more information, you can refer to his paper “A Meshfree Approach for Dynamic Analysis of Sandwich Conical and Cylindrical Shells with Varying Thicknesses” in “Acta Mechanica Solida Sinica” (SCI).
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Jo Feb 14, 2025
Rapid development of information technology has greatly changed the pattern of teaching and learning in education, and e-learning is the most widely used mode of learning nowadays. In e-learning systems, some cheating phenomena can occur because the teacher cannot see the students' learning process. User authentication by user names and passwords only when logging on in most e-learning systems might cause cheating. In other words, someone else may substitute for learners, and the learner may leave before the lecture is over.
If a student enrolled in e-learning system is able to complete a course without actually learning, the reliability of the course and e-learning system is diminished, and since lectures or learning materials are intellectual assets, such deception should be prevented. Therefore, in e-learning systems, it is necessary to identify the learner during the learning activities as well. To detect spoofing in e-learning is of great significance in enhancing the reliability of e-learning systems and protecting the copyright of learning content.
Therefore, biometric authentication techniques such as face recognition, fingerprint recognition and speech recognition have been introduced into user identification in e-learning systems, and prevention of spoofing of learning by face recognition in e-learning process is in active use. However, face recognition is usually conducted at the beginning of user engagement, lectures and tests, and there has been no intense research to prevent spoofing of learning in the learning process.
Ryu Chang Sik, a section head at the Faculty of Distance Education, has proposed a new method to prevent spoofing, based on implicit face matching at randomly selected time intervals during online learning.
In the proposed method, face-matching identification is performed at the time of system login and the beginning of learning, and in each learning process (e.g., learning a section). In addition, implicit face-matching is performed several times without interaction with students at random time intervals to calculate the similarity value and detect the impostor. If not detected in the random check, explicit user identification would be required.
The proposed method has been applied to an e-learning system that provides a graduate qualification. The result shows that the system can effectively distribute the server load and prevent the spoofing of learning, while significantly reducing the number of stoppage of learning due to face contrasts.
You can find more information in his paper “Identification of Spoofing in e-Learning system with the implicit face recognition” in “INFORMATICA”.
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Jo Feb 13, 2025
At present, since energy depletion and environmental pollution are global issues, many attempts have been made to produce light olefins by low energy consumption, low carbon dioxide emission and environment-friendly methods from coal and natural gas which is more abundant than petroleum or from sustainable biomass resources. One of these methods is the methanol to olefins (MTO) process using a microporous catalyst.
Dimethyl ether (DME) is an intermediate of MTO, and it is easily converted to olefins by catalysis, a surface phenomenon. The key of DTO technology is to synthesize catalysts with high light olefins selectivity and long lifetime. SAPO-18 structure that is extensively used in MTO, DTO, CO2/CH4 separation and SCR of NOx processes, and is structurally similar to SAPO-34 (with CHA framework).
Many attempts have been made to enhance the catalytic performance and lifetime of SAPO-18 catalysts, such as synthesis of catalysts with different organic structure directing agent (OSDA), incorporation of nonmetallic and metallic elements into the framework, and the mechanism of coke formation, but the role of post-acid treatment on DTO performance of SAPO-18 has been barely addressed.
Jong Song Chol, a researcher at the Faculty of Chemical Engineering, has proposed post-HCl treatment as a method to promote DTO performance of SAPO-18, and compared with S-0 and NiS-0 the catalytic performance of acid-treated catalysts such as crystalline structure, morphology, specific surface area, textural properties, acidity and DTO performance.
He has found that the optimum HCl concentration and treating time of SAPO-18 catalyst for the catalytic performance enhancement in DTO are 0.1M and 3h, respectively.
You can find the details in his paper “Efficient post-HCl treatment for promoting DTO performance of SAPO-18 and Ni-substituted SAPO-18” in “Journal of Saudi Chemical Society” (SCI).
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Jo Feb 12, 2025
IGBT, a high-voltage high-power integrated circuit device, has a wide range of high-power switching applications such as mobile driving, power supply, railway transportation, industry control, etc. NPT-IGBT is a composite device of MOSFET and BJT.
Since NPT-IGBT usually operates at high voltage and high current, hot-carrier-induced degradation will be generated inside the device. Hot carriers with high energy will damage the oxide region of the device and the interface between silicon and silicon-dioxide, and increase the trap charge of the interface and the oxide region.
Although many researchers have described the issues on hot carriers of IGBT device, little literature is on the reliability of hot carrier of NPT-IGBT.
Kim Hak Bong, a section head at the Semiconductor Institute, has analyzed the degradation mechanisms due to the hot carrier effect in NPT-IGBT through the voltage stress measurement, TCAD simulation and charge pumping measurement.
He has concluded the following from the results. First, the device might have different degradation mechanisms under different gate voltage conditions. Second, when the gate voltage is relatively high, degradation is caused in three regions. The boundary state is generated in the body region, while the oxide layer trap charge is caused in the accumulation region, the field-oxide region and the drift region. Third, when the gate voltage is relatively low, the boundary state and the oxide layer trap charge are formed in the drift region and the degradation in the body region is relatively small.
If more information is needed, please refer to his paper “Analysis on Effect of Hot-Carrier-Induced Degradation of NPT-IGBT” in “Solid-State Electronics” (SCI).
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