Indirect Determination of Free Chlorine in Seawater...

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).

Sinogram Restoration based on Shape Property

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).

Dynamic Analysis of Sandwich Shells with Varying Th...

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).