• Journal of Environmental Health Sciences
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• v.35 no.5
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• pp.376-385
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• 2009

The characteristics of Lake Cheonhoji water and sediment were investigated in oder to utilize these as fundamental materials for the management of lake water quality. The hydrographic properties of Lake Cheonhoji which are relatively low chance of nutrients loading from the watershed and a long retention time of lake water, lead to the probability of high lake productivity. It was also observed that lake water showed stratification during summer and complete mixing during fall, even though water depth was relatively shallow. The trophic state was eutrophic to hypertrophic from summer to late fall. The overall properties of the sediment were oligohumic, high ignition loss and high composition of NAIP and Resid.-P, which might serve as potential pollution sources of lake water quality. In laboratory scale experiments, it was observed that leaching potential of nutrients in the sediment was greatly dependant upon water temperature and dissolved oxygen. Finally, water pollution in Lake Cheonhoji was considered to be largely due to the adverse cycle of uncontrollable eutrophication, which resulted in the subsequent occurrence of dead algae and animal plankton, organic sedimentation, reduction of dissolved oxygen and nutrients leaching, which again reinforced the cycle of eutrophication in the lake.

• Environmental Analysis Health and Toxicology
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• v.24 no.1
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• pp.33-41
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• 2009

Among the toxicants in the environment dioxin-like compounds, including TCDD(2,3,7,8-Tetrachlorodibenzo-p-Dioxin), are well known as carcinogen and teratogen. TCDD the most toxic of these compounds, may result in a wide variety of adverse health effects in humans and environment, including carconogenesis, hepatotoxicity, teratogenesis, and immunotoxicity. Also TCDD increases superoxide, peroxide radicals and induces oxidative stress that leads to breakage of DNA single-strand and mitochondrial dysfunction. Recently, there have been reports that persistent organic pollutants(POPs) may be causing metabolic disease through mitochondrial toxicity. In order to examine if dioxin brings about toxicity on mitochondria directly, we measured the change of the mitochondrial membrane potential after exposure to TCDD using JC-1 dye. After short time exposure of dioxin, mitochondrial depolarization was observed but it recovered to the control level immediately. This TCDD effect on mitochondrial membrane potential was not correlated either to the production of reactive oxygen species(ROS) or extracellular $Ca^{2+}$ by TCDD. Less than 2 hours exposure of TCDD did not show any change in ROS production but 0.25 nM TCDD for 48 hours or 0.5 nM TCDD for 12 hours exposure did increase in ROS production. Under these conditions of ROS production by TCDD, no changes in the mitochondrial membrane potential by TCDD was observed.

• Corrosion Science and Technology
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• v.2 no.4
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• pp.178-182
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• 2003

Slow Strain Rate Tests (SSRT) were carried out to investigate the effect of environmental factors on the Stress Corrosion Cracking (SCC) susceptibility of 3.5NiCrMoV steels used in discs for Low-Pressure (LP) steam turbines in electric power generating plants. The influences of dissolved oxygen on the stress corrosion cracking of turbine steel were studied, For this purpose, specimens were strained at variously oxygenated conditions at $150^{\circ}C$ in pure water. When the specimen was strained with $1{\times}10^{-7}s^{-1}$ at $150^{\circ}C$ in pure water, increasing concentration of dissolved oxygen decreased the elongation and the UTS. The corrosion potential and the corrosion rare increased as the amounts of dissolved oxygen increased. The increase of the SCC susceptibility of the turbine steel in a highly dissolved oxygen environment is due to the non protectiveness of the oxide layer on the turbine steel surface and the increase of the corrosion current. These results clearly indicate that oxygen concentration increases Stress Corrosion Cracking susceptibility in turbine steel at $150^{\circ}C$.

• Journal of the Korean Electrochemical Society
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• v.3 no.4
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• pp.191-195
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• 2000

Electrochemical properties of the oxygen electrode in phosphoric acid fuel cell have been studied using AC impedance method as a function of applied potential, operating temperature and teflon content in the electrode. The oxygen electrode reaction in the $105wt.\%$ phosphoric acid is characterized by a parallel resistive component, $R_p$ and a capacitive component, $C_p$ with serial electrolyte resistance, $R_s$. The conductivity of the phosphoric acid is found to be 0.31-0.47 S/cm in the range of $130\;to\;190^{\circ}C$ from the measured impedance. The increase of applied potential and temperature produced the decreased RP and the increased $C_p$, which means the increase of the oxygen electrode reaction rate. The single cells with the cathode of various teflon contents were tested, and the cathode with $40wt.\%$ teflon showed good performance, which is considered to be related to an optimized impedance behavior.

• Ocean and Polar Research
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• v.35 no.3
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• pp.229-237
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• 2013

We measured two-dimensional (2-D) oxygen distribution in the surface sediment layer of intertidal sediment using a simple and inexpensive planar oxygen optode, which is based on a color ratiometric image approach. The recorded emission intensity of red color luminophore light significantly changed with oxygen concentration by $O_2$ quenching of platinum(II)octaethylporphyrin (PtOEP). The ratios between the intensity of red and green emissions with oxygen concentration variation demonstrated the Stern-Volmer relationship. The 2-D oxygen distribution image showed microtopographic structure, diffusivity boundary layer and burrow in surface sediment layer. The oxygen penetration depth (OPD) was about 2 mm and the one-dimensional vertical diffusive oxygen uptake (DOU) was 12.6 mmol $m^{-2}d^{-1}$ in the undisturbed surface sediment layer. However, those were enhanced near burrow by benthic fauna, and the OPD was two times deeper and DOU was increased by 34%. The simple and inexpensive oxygen planar optode has great application potential in the study of oxygen dynamics with high spatiotemporal resolution, in benthic boundary layers.

• Journal of the Korean Electrochemical Society
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• v.13 no.1
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• pp.45-49
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• 2010

The rechargeable Zn-air battery is considered as one of the potential candidates for the next generation secondary batteries due to its many advantages. However, its further applications and commercialization have been limited by the complexity of the reactions on air electrode which are oxygen reduction and evolution reactions (ORR/OER) upon discharging and charging processes, respectively. In the present study, lanthanum was impregnated into a commercial Pt/C gas diffusion electrode, and it clearly verified significantly enhanced cycling stability and reversibility. The results presented in this study show the possibility of repeated charge/discharge processes for Zn-air batteries with a La-loaded air electrode, and they demonstrate the potential as a promising next generation secondary battery.

• Toxicological Research
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• v.23 no.3
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• pp.215-221
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• 2007

Although sanguinarine, a benzophenanthridine alkaloid, possesses anti-cancer properties against several cancer cell lines, the molecular mechanisms by which it inhibits cell growth and induces apoptosis have not been clearly understood. In order to further explore the critical events leading to apoptosis in sanguinarine-treated MCF-7 human breast carcinoma cells, the following effects of sanguinarine on components of the mitochondrial apoptotic pathway were examined: generation of reactive oxygen species (ROS), alteration of the mitochondrial membrane potential (MMP), and the expression changes of Bcl-2 family proteins. We show that sanguinarine-induced apoptosis is accompanied by the generation of intracellular ROS and disruption of MMP as well as an increase in pro-apoptotic Bax expression and a decrease of anti-apoptotic Bcl-2 and Bcl-xL expression. The quenching of ROS generation with N-acetyl-L-cysteine, the ROS scavenger, protected the sanguinarine-elicited ROS generation, mitochondrial dysfunction, modulation of Bcl-2 family proteins, and apoptosis. Based on these results, we propose that the cellular ROS generation plays a pivotal role in the initiation of sanguinarine-triggered apoptotic death.

• Journal of Powder Materials
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• v.24 no.2
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• pp.96-101
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• 2017

Well-dispersed platinum catalysts on ruthenium oxide nanofiber supports are fabricated using electrospinning, post-calcination, and reduction methods. To obtain the well-dispersed platinum catalysts, the surface of the nanofiber supports is modified using post-calcination. The structures, morphologies, crystal structures, chemical bonding energies, and electrochemical performance of the catalysts are investigated. The optimized catalysts show well-dispersed platinum nanoparticles (1-2 nm) on the nanofiber supports as well as a uniform network structure. In particular, the well-dispersed platinum catalysts on the ruthenium oxide nanofiber supports display excellent catalytic activity for oxygen reduction reactions with a half-wave potential ($E_{1/2}$) of 0.57 V and outstanding long-term stability after 2000 cycles, resulting in a lower $E_{1/2}$ potential degradation of 19 mV. The enhanced electrochemical performance for oxygen reduction reactions results from the well-dispersed platinum catalysts and unique nanofiber supports.

• Corrosion Science and Technology
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• v.3 no.6
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• pp.227-232
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• 2004

The carboxylates as a corrosion inhibitor has been studied by many researchers because of its environmental safety and low depletion rate. However, conventional test methods of inhibitor such as weight loss measurements, linear polarization resistance and corrosion potential monitoring etc., evaluate uniform corrosion of metals. These methods are unable to evaluate crevice-related corrosions, which are encountered in most of heat exchanging facilities. In order to choose the optimum corrosion inhibitor, the appropriate test methods are required to evaluate their performances in service environment. From this point of view, polarization technique was used to evaluate the characteristics of sodium heptanoate on corrosion behavior for carbon steel. Especially a thin film crevice sensor technique were applied to simulate the crevice corrosion in this study. From these experiments, we found that oxygen as an oxidizing agent was required to obtain stable passive film on the metal. Presence of oxygen, however, accelerated crevice corrosion. Potential shift by oxygen depletion and weakened inhibitive film inside the crevice were responsible for such accelerated feature. It is shown that film for corrosion inhibition is a mixture of sodium heptanoate and iron (II) heptanoate as reaction product of iron surface and sodium heptanoate. The iron (II) heptanoate which has been synthesized by reaction of heptanoic acid and ferrous chloride in methanol solution forms bidentate complex.

• Journal of Korean Port Research
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• v.14 no.4
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• pp.475-479
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• 2000

A possibility of the implementation of a quartz crystal sensor to the determination of chemical oxygen demand is examined by checking the electrochemical behavior of the sensor in a glucose solution. Since the surface of a quartz crystal has to be oxidized, a relatively active metal is coated on the surface of a usual 9 MHz AT-cut crystal. The electrochemical behavior is investigated by measuring the changes of current, resonant frequency and resonant resistance while a constant potential is applied. The crystal is installed in a specially designed container, and a quartz crystal analyzer is utilized to measure the frequency and resistance simultaneously. The variations of the measurements are examined at different concentrations of glucose solution, and a proper relation between the concentrations of glucose solution, and a proper relation between the concentration and the measurements is analyzed. As a result, it is found that a linear relation between the concentration of less than 900 ppm and the peak current when a constant potential of -180 mV (SSCE) is applied. The relation can be utilized for the determination of glucose concentration in sea water, and considering a direct relation between gluose concentration and chemical oxygen demand tells a possibility of the measurement of chemical oxygen demand using quartz crystal oscillators.