• Bulletin of the Korean Chemical Society
• /
• v.9 no.4
• /
• pp.213-217
• /
• 1988

A new paradigm for the viscosity of fluid is presented by considering the fact that the viscosity is equal to the shear stress divided by the shear rate. The shear stress is obtained from the sum of kinetic and internal pressures of fluid, and the shear rate is found from the phonon velocity divided by the mean free path of the phonon. The calculated viscosities for various simple substances are in excellent agreements with those of the observed data through the wide temperature range covered both of liquid and gas phase.

• Bulletin of the Korean Chemical Society
• /
• v.22 no.5
• /
• pp.514-518
• /
• 2001

We have explored the importance of two ATP binding domains of Hsp104 protein in protection of yeast cells from cadmium exposure. In the previous study we have discovered that the presence of two ATP binding sites was essential in providing heat sh ock protection as well as rescuing cells from oxidative stress. In this paper we first report wild type cell with functional hsp104 gene is more resistant to cadmium stress than hsp104-deleted mutant cell, judging from decrease in survival rates as a result of cadmium exposure. In order to demonstrate functional role of two ATP binding sites in cadmium defense, we have transformed both wild type (SP1) and hyperactivated ras mutant (IR2.5) strains with several plasmids differing in the presence of ATP binding sites. When an extra copy of functional hsp104 gene with both ATP binding sites was overexpressed with GPD-promoter, cells showed increased survival rate against cadmium stress than mutants with ATP binding sites changed. The degree of protection in the presence of two ATP binding sites was similarly observed in ira2-deleted hyperactivated ras mutant, which was more sensitive to oxidative stress than wild type cell. We have concluded that the greater sensitivity to cadmium stress in the absence of two ATP binding sites is attributed to the higher concentration of reactive oxygen species (ROS) produced by cadmium exposure based on the fluorescence tests. These findings, taken all together, imply that the mechanism by which cadmium put forth toxic effects may be closely associated with the oxidative stress, which is regulated independently of the Ras-cAMP pathway. Our study provides a better understanding of cadmium defense itself and cross-talks between oxidative stress and metal stress, which can be applied to control human diseases due to similar toxic environments.

• Journal of the Korean Chemical Society
• /
• v.67 no.6
• /
• pp.462-474
• /
• 2023

The purpose of this study is to analyze the stress experienced by pre-service chemistry teachers during their teaching practice. To do this, a stress test tool for pre-service science teachers was developed, and a survey was conducted with 19 pre-service chemistry teachers to investigate their anticipated stress before the practice and the stress experienced after the practice. The survey, conducted online before and after the teaching practice, was analyzed using descriptive statistics. The interpretation of the stress test results for pre-service chemistry teachers was based on teaching portfolios and interview data compiled during the teaching practice. The research findings are as follows: First, pre-service chemistry teachers anticipated various stresses before the teaching practice, but the number of stress factors and the number of pre-service teachers experiencing stress were generally lower during the practice. Second, there are a difference in the factors and percentage of anticipated and experienced stress before and during the teaching practice depending on the school level where pre-service chemistry teachers gained their practice. Third, there was no gender difference in the stress experienced by pre-service chemistry teachers during the teaching practice.

• Korea-Australia Rheology Journal
• /
• v.21 no.2
• /
• pp.83-89
• /
• 2009

Coating process plays an important role in information technology such as display, battery, chip manufacturing and so on. However, due to complexity of coating material and fast deformation of the coating flow, the process is hard to control and it is difficult to maintain the desired quality of the products. Moreover, it is hard to measure the coating process because of severe processing conditions such as high drying temperature, high deformation coating flow, and sensitivity to the processing variables etc. In this article, the coating process is to be re-illuminated from the rheological perspectives. The practical approach to analyze and quantify the coating process is discussed with respect to coating materials, coating flow and drying process. The ideas on the rheology control of coating materials, pressure and wet thickness control in patch coating process, and stress measurement during drying process will be discussed.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.04a
• /
• pp.180-183
• /
• 2003

In this work. a potential inexpensive epoxy resin. epoxidized soybean oil (ESO) was synthesized and applied as a toughening agent for 4.4'-tetradiglycidyl diaminodiphenyl methane (TGDDM). The chemical structure of ESO was characterized by FT-IR, $^1H NMR, and ^{13}C NMR$ spectroscopy. The curing behaviors. thermal stabilities. fracture toughness. and flexural strength of TGDDM/ESO blend systems were investigated by using the dynamic DSC. thermogravimetric analysis (TGA). and flexural tests. The thermal stabilities of TGDDM/ESO blend systems were decreased with increasing ESO contents. whereas the critical stress intensity factor ($K_{IC}$) and flexural strength ($\sigma_f$) were increased with ESO contents up to 10 wt% ESO.

• Proceedings of the KIEE Conference
• /
• 2005.07c
• /
• pp.1912-1914
• /
• 2005

The electrical, chemical and mechanical characteristics in transformer insulations are changed due to thermal stress. It is known that characteristics of transformer insulations is deteriorated such as decrease of dielectric strength, deterioration of dielectric constant and tensile strength of paper as transformer oil and paper are aged by thermal stress. Furthermore, chemical characteristics of them are deteriorated as like increment of moisture contents and dissolved by-products in oil, etc. In this paper we have been investigated chemical characteristics of transformer by accelerated thermal aging. For this working we have made experimental test cell and aged at a temperature up to $140^{\circ}C$ for 500 hours. The oil-paper insulation samples have been measured at intervals of 100 hours. For analysis we used Karl-Fisher titration method and high performance liquid chromatography (HPLC).

• Proceedings of the Korean Geotechical Society Conference
• /
• 1996.12a
• /
• pp.67-78
• /
• 1996

• Proceedings of the Korean Society of Rheology Conference
• /
• 2001.09a
• /
• pp.154.1-154
• /
• 2001

(No abstract, see full-text)

• Proceedings of the Korean Society of Rheology Conference
• /
• 2001.09a
• /
• pp.154.3-154
• /
• 2001

(No abstract, see full-text)

• Bulletin of the Korean Chemical Society
• /
• v.22 no.11
• /
• pp.1175-1176
• /
• 2001