Jo Feb 21, 2025
Microbubbles are widely used in various fields including fishing industry, agriculture, chemical industry and light industry in the world and brisk researches have been conducted to improve their performance.
There are several methods for generating microbubbles, depending on their principles and applications. They are largely divided into two modes―one is liquid flow accompanying and the other is non-liquid flow accompanying. Liquid flow accompanying includes swirl jet, mechanical high-speed cutting, pressurized melting and Venturi, and non-liquid flow accompanying includes fluid oscillation, ultrasonic, electrolytic, etc.
Compared with the methods described above, the pressurized-dissolved microbubble generator has the advantage of high bubble generation and relatively small and uniform size distribution.
Han Il Song, a researcher at the Nano Science and Technology Institute, has manufactured a large microbubble generator that can be widely applied in various fields including wastewater treatment, sewage treatment and fishery by generating relatively small and uniform microbubbles at high density by means of a pressurized solution method.
The pressurized-dissolved microbubble generator used for pulp mill effluent treatment has the advantage of low cost and operating cost but very high efficiency of microbubble generation.
The new-type microbubble generator consists of a mixing tank, a circulating water pump, a Venturi air inlet, a pressurized tank, and a swirl jet nozzle.
The Venturi air intake unit, which is located at the inlet of the circulating water pump, is equipped with a flow control valve to provide a flow rate of 45-50L/min of air to be sucked.
The application of a pressurized-dissolved microbubble generator to pulp effluent treatment resulted in pulp recovery of more than 92% and the residual pulp content in the wastewater discharged after treatment of less than 0.002%.
At present, a large pressurized-dissolved microbubble generator has been introduced into pulp wastewater treatment to recover residual pulp in wastewater with higher efficiency than 92%, thus contributing greatly to recycling pulp and protecting the ecological environment.
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Jo Feb 20, 2025
It is very important to improve the quality of communication lines.
Communication lines, that is, telephone lines should have not only high electrical conductivity but also high strength.
The use of copper-coated wires with low resistivity as communication wires has become a worldwide trend.
The wire used for communication should have a low wire resistance, as well as a good current flow, and a limited diameter wire should be coated with a copper deposit of a certain thickness.
Therefore, the crystal should be compact and the thickness should be uniform.
The wire used as a telephone wire is very thin with the diameter of 0.235-0.24 mm, so it cannot be used at high temperatures and it must have a certain thickness to obtain appropriate resistivity. If it is too thin or too thick, its resistivity increases.
Kim Kyong Chol, a section head at the Faculty of Chemical Engineering Faculty, has designed and established a high-speed continuous copper coating process for producing wire by depositing copper of uniform thickness on the surface of a steel wire by the electroplating method at the time of continuous draw of steel wire.
To ensure the copper plating layer thickness of 0.015mm on the steel wire, he set the plating process in two stages and fixed the anode contact at 2m intervals, and carried out degreasing, neutralization, plating and passivation continuously.
For constant immersion length in the plating solution, he set the reciprocating of wire to be 1.5 times.
When the number of outgoing wires is 6 and the outgoing speed is 10~15m/min, the resistance value of the steel wire copper coating is 1.6~2Ω/m, and the resistivity is 0.08~0.1Ω·mm2/m.
The proposed method is widely used in the units for copper plating of 0.2-0.5mm steel wire, especially in the plants for producing copper coating steel wire for communication.
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Jo Feb 19, 2025
Fractional calculus is a branch of mathematics that deals with the differentiation and integration of any arbitrary order. Fractional differential equations have been widely applied to the analysis of complex systems such as material mechanics, anomalous diffusion, wave propagation and turbulence analysis, and researches on this field have attracted more and more attention in recent years. The variable order fractional calculus is the extension of the constant order fractional calculus. Here, fractional order is expressed not as a constant but in the form of a function of time or space variables.
Variable order fractional derivatives have significant advantages over constant order fractional derivatives in analyzing and controlling various physical systems including a nonlinear viscoelasticity oscillator.
Since numerical schemes with high degree of accuracy for variable order fractional derivatives can improve the accuracy of calculations and reduce computational cost, developing these numerical schemes is of great practical importance.
O Chol Won, a researcher at the Faculty of Applied Mathematics, has presented an explicit finite difference method for a space-time Riesz-Caputo variable order fractional wave equation.
He has proved that the explicit finite difference scheme is stable under certain constraints and estimated global truncation error. The numerical example shows the efficiency of the proposed finite difference scheme.
For further details, you can refer to his paper “An Explicit Finite Difference Approximation for Space-Time Riesz–Caputo Variable Order Fractional Wave Equation Using Hermitian Interpolation” in “NUMERICAL ANALYSIS AND APPLICATIONS” (SCI).
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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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