• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.155-162
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• 2012

When RC (Reinforced Concrete) structures are exposed to sea water, steel corrosion can occur and this leads a degradation of structural performance. Referring the electro-deposition system with sea water from the 1st step research, durability and structural performance are evaluated in coated steel and RC members containing it in the 2nd research. In the durability performance test, Half Cell Potential test is performed and the coated steel is evaluated to have the high resistance to corrosion, which shows only 35% of corrosion velocity in normal (bare) steel. In the structural performance test, tensile strength, adhesive strength, and flexural/shear in RC member are performed. For the electro-deposit coated steel, increasing ratios of 3.2% and 8.8% are evaluated in the test of tensile strength and adhesive strength, respectively. For the structural test in RC member, there is no big difference between RC members with coated and non-coated steel in ultimate load and failure pattern It is evaluated that the chemical compound with $CaCO_3$ and $Mg(OH)_2$ from electro-deposition causes slightly increased structural performance. The electro-deposit coated steel can be more widely applied after performance verification from several tests like fatigue, resistance to impact, and long term-submerging test.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.585-588
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• 2008

To predict the service life of reinforced concrete structures exposed to chloride environment, quantitative measures of material properties such as the critical chloride content for corrosion in concrete and the diffusion coefficient of chloride ions of concrete and the surface chloride content of the concrete are essential. However, it should be noted that they are influenced by several factors such as concrete mix proportions, cement type, and environmental conditions, etc. Thus, the purpose of this research is to estimate more actually the critical chloride content for corrosion of the reinforcing steel in concrete by field exposure experiment. For this purpose, the prism concrete test specimens were made for water-cement(W/C) ratios of 31%, 42%, 50%, and 70%, and then the field exposure experiment for them were conducted at Youngduk of the east coast for about 3 years. During the test, corrosion monitoring by half cell potential method was carried out to detect the time to initiation of corrosion for test specimens and its chloride content was evaluated by breaking the concrete test specimens when corrosion of the reinforcing steel in concrete was perceived. It was observed from the test results that the critical chloride content for corrosion of reinforcing steel in concrete would be dependent on W/C ratio and almost irrespective of concrete cover.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.1
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• pp.131-143
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• 2007

Statement of the problem: In case of poor bone quality or immediately loaded implant, various strategies have been developed focusing on the surface of materials to improve direct implant fixation to the bone. The microscopic properties of implant surfaces play a major role in the osseous healing of dental implant. Purpose of study: This study was undertaken to evaluate bone response of ion beam-assisted deposition(IBAD) of hydroxyapatite(HA) on the anodized surface of subperiosteal titanium implants. Material and methods: Two half doughnut shape subperiosteal titanium implants were made. The control group was treated with Anodized surface treatment and the test group was treated with IBAD of HA on control surface. Then two implants inserted together into the subperiosteum of the skull of 30 rats and histological response around implant was observed under LM(light microscope) and TEM(transmission electron microscope) on 4th, 6th and 8th week. Results: Many subperiosteal implants were fixed with fibrous connective tissue not with bony tissue because of weak primary stability. The control group observed poor bone response and there was no significant change at any observation time. However the test group showed advanced bone formation and showed direct bone to implant contact under LM on 8th week. The test group observed much rER in the cell of osteoblast but the control group showed little rER under TEM. Conclusions: The test group showed better bone formation than the control group at the condition of weak primary stability. With these results IBAD surface treatment method on Anodized surface, may be good effect at the condition of weak primary stability.

• Analytical Science and Technology
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• v.14 no.4
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• pp.364-370
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• 2001

The corrosion behaviors of reinforcing steels were investigated under chloride ion contained in cement mortar including gypsum by the implementation of half cell potential measurement, EPMA analysis, exterior features, weight loss and extraction experiment. The acceleration test equipment accelerated corrosion of mild steel bar in a short period of time. From observing the exterior features and weight loss, we could evaluate the measure of corrosion. Also, from the extraction experiment of ${SO_4}^{2-}$ with $Cl^-$ ions contained in the ceramic mortar, we concluded that ${SO_4}^{2-}$ ion affected more on the corrosion mechanism in comparison to pH.

• Journal of Power Electronics
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• v.17 no.2
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• pp.490-500
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• 2017

Fuel cell (FC) is a promising power supply in electric vehicles (EV); however, it has poor dynamic performance and short service life. To address these shortcomings, a super capacitor (SC) is adopted as an auxiliary power supply. In this study, the frequency decoupling control method is used in electric vehicle energy system. High-frequency and low-frequency demand power is provided by SC and FC, respectively, which makes full use of two power supplies. Simultaneously, the energy system still has rapidity and reliability. The distributed power system (DPS) of EV requires DC-DC converters to achieve the desired voltage. The stability of cascaded converters must be assessed. Impedance-based methods are effective in the stability analysis of DPS. In this study, closed-loop impedances of interleaved half-bridge DC-DC converter and phase-shifted full-bridge DC-DC converter based on the frequency decoupling control method are derived. The closed-loop impedance of an inverter for permanent magnet synchronous motor based on space vector modulation control method is also derived. An improved Middlebrook criterion is used to assess and adjust the stability of the energy system. A theoretical analysis and simulation test are provided to demonstrate the feasibility of the energy management system and the control method.

• 대한예방의학회:학술대회논문집
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• 1994.02a
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• pp.431-438
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• 1994

As currently conducted, standard rodent bioassays do not provide sufficient information to assess carcinogenic risk to humans at doses thousands of times below the maximum tolerated dose. Recent analyses indicate that measures of carcinogenic potency from these tests are restricted to a narrow range about the maximum tolerated dose and that information on shape of the dose-response is limited in experiments with only two doses and a control. Extrapolation from high to low doses should be based on an understanding of the mechanisms of carcinogenesis. We have postulated that administration of the maximum tolerated dose can increase mitogenesis which, in turn. increases rates of mutagenesis and, thus, carcinogenesis. The animal data are consistent with this mechanism, because about half of all chemicals tested are indeed rodent carcinogens, and about 40% of the positives are not detectably mutagenic. Thus, at low doses where cell killing does not occur, the hazards to humans of rodent carcinogens may be much lower than commonly assumed. In contrast, for high-dose exposures in the workplace, assessment of hazard requires comparatively little extrapolation. Nevertheless. permitted workplace exposures are sometimes close to the tumorigenic dose-rate in animal tests. Regulatory policy to prevent human cancer has primarily addressed synthetic chemicals, yet similar proportions of natural chemicals and synthetic chemicals test positive in rodent studies as expected from an understanding of toxicological defenses, and the vast proportion of human exposures are to natural chemicals. Thus, human exposures to rodent carcinogens are common. The natural chemicals are the control to evaluate regulatory strategies, and the possible hazards from synthetic chemicals should be compared to the possible hazards from natural chemicals. Qualitative extrapolation of the carcinogenic response between species has been investigated by comparing two closely related species: rats and mice. Overall predictive values provide moderate confidence in interspecies extrapolation; however, knowing that a chemical is positive at any site in one species gives only about a 50% chance that it will be positive at the same site in the other species.

• Journal of the Korean Electrochemical Society
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• v.15 no.1
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• pp.12-18
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• 2012

The prohibitively high cost of Pt catalyst might be the biggest barrier for the commercialization of proton exchange membrane fuel cells (PEMFC) of which wide application is expected. Worldwide research efforts for the development of alternative to Pt oxygen reduction reaction (ORR) catalyst are made recently. One of the important considerations in the catalyst development is durability issue as well as economic aspect. From this point of view, platinum group metals (PGM) except Pt can be a candidate for replacing Pt catalyst because the material properties and the catalytic activity of PGM are expected to be similar to Pt. In contrast to Ir, Rh and Os to which not so much attention has been paid as an ORR catalyst, Pd that is most similar to Pt in terms of material properties and catalytic activity and Ru that is in the form of chalcogenide have been studied intensively. Activity comparison between non-Pt and Pt oxygen reduction catalysts by half cell test using RDE (rotating disk electrode) or PEMFC MEA (membrane electrode assembly) operation indicates that Pd-based catalysts show the most similar activity to Pt. In this paper we analyze the composition of PGM ORR catalyst in literature to promote the development of non-Pt ORR catalyst.

• Membrane Journal
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• v.18 no.1
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• pp.75-83
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• 2008

In this research, the research for enhancing the stability at the mechanical strength and thermal stability and high power through the Direct Fluorination of the Polyethylene (PE, Asahi) for secondary battery was conducted. The surface of according to the fluorine gas exposure time and constructional change were observed through the scanning electron microscope image, and the contact angle. The mechanical property was confirmed through the tensile strength and surface hydrophilic property experiment. Charge and discharge experiment, the lifetime property, and the overcharge test were performed in order to confirm the electrochemical characteristic of produced and we confirmed at the high power that the stability about a temperature was improved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.303-303
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• 2008

$LiMn_2O_4$는 출력특성이 좋고 가격이 저렴하지만 전해액 중에서 $Mn^{2+}$이 용출되어 나오는 것과 반복적인 충방전시 구조가 파괴되는 단점이 있어 이것을 보완하고자 $FePO_4\cdot2H_2O$를 $LiMn_2O_4$의 표면에 코팅하였다, $LiMn_2O_4$를 모재로, $FePO_4\cdot2H_2O$를 코팅재로 사용하여 $FePO_4\cdot2H_2O$의 코팅량 변화와, 열처리 온도변화에 따른 물성 변화를살펴보았다, LiOH 와 $MnO_2$의 혼합물을 $1000^{\circ}C$ 에서 소성하여 $LiMn_2O_4$를 합성하고, Fe$(NO_3)_3$ 수용액과 $NH_4H_2PO_4$ 수용액을 혼합하여 $FePO_4\cdot2H_2O$를 제조하였다, $LiMn_2O_4$에 $FePO_4\cdot2H_2O$를 1wt%, 2wt%, 3wt% 비율로 ball milling 을 통해 코팅한 후, 온도를 변화시키면서 열처리 하였다. 코팅한 물질을 XRD를 통해 구조를 분석하고 SEM을 이용하여 형상을 관찰하였다. 또한 고온에서의 $Mn^{2+}$의 용출량을 ICP로 측정하고 half-cell을 만들어 충방전 test를 통해 충방전 특성을 조사하였다. 아울러, 코팅량과 열처리 온도 등 합성변수들이 소재특성 및 전기화학적 특성에 미치는 영향을 조사하였다.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3567-3572
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• 2010

Black pine barks from the southern region of Korea were extracted using pressurized hot water and the water soluble extracts were then separated in a stepwise fashion using a variety of solvents, column chromatography (CC), thin layer chromatography (TLC), and high pressure liquid chromatography (HPLC). The antioxidant activities of each fraction and the active compounds were determined based on the radical scavenging activities of 2,2-diphenyl-1-picrylhydrazyl (DPPH), reductive potential of ferric ion, and total phenol contents. A DPPH test showed that the half maximal effective concentration ($EC_{50}$ value : $6.59{\pm}0.31\;{\mu}g/mL$) of the ethyl acetate fraction (ca. 0.67%) was almost the same as that of the control compounds and inversely proportional to the value of the total phenol contents. The cell viability of the water extracts was confirmed by methyl thiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) with enzyme linked immune sorbent assay (ELISA). Catechin, epicatechin, quercetin and ferulic acid were isolated from the ethyl acetate fraction as active compounds and identified by nuclear magnetic resonance. The antioxidant activity as value of DPPH of each of the separated compounds was lower than the ethyl acetate fraction, and ferulic acid was the lowest among these compounds.