• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.1
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• pp.22-31
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• 1997

The grain boundary etching method as a method for assessing degradation of structural materials has received much attention because it is simple, inexpensive and easy to apply to real components. In this study, the effectiveness of the method is verified by successfully applying the technique to in-service components of aged fossil power plants such as main steam pipes, boiler headers an turbine rotors. A new degradation parameter, intersecting number ratio (N$_{1}$/N$_{0}$), is employed. The intersecting number ratio (N$_{1}$/N$_{0}$) is defined as the ratio of intersection number (N$_{1}$) obtained from 5-minute picric acid etched surface to the number (N$_{0}$) obtained from nital etched surface. Two kinds of test materials, 2.25Cr-1Mo steel and 1Cr-1Mo-0.25V steel, were artificially thermal-aged at 630.deg. C in different levels of degradation., (N$_{1}$/N$_{0}$) were measured. And, correlations between the measured values and LMP values calculated from aging temperature and aging time were sought. To check the validity of the correlations obtained in laboratory, similar data were measured from service components in four old Korean fossil power plants. These on-site measurement data were in good correlation with those obtained in the laboratory.oratory.

• Fire Science and Engineering
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• v.15 no.4
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• pp.78-85
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• 2001

This dissertation is research on the fireproof characteristic of molded transformer and the extinguishable characteristics of the NAF S-III. As the research method, a theoretical examination has been made for the combustion process of epoxy resin, which was the main material of molded transformer, and extinguishing process of NAF S-III, which has recently been used in the clean extinguishable chemicals. Furthermore, for its proof, the experiments on combustion and extin-guishment on molded transformer has been performed. By installing the actual molded transformer in and artificial the horizontal heating furnace which has similar conditions with the electrical substation, and after subsequently ignited, the extinguishing process has been observed by classifying it into the natural extinguishment of the ignited transformer, and extinguishable chemical in NAF S-III has been injected. The volume of injected extinguishable chemical was the economical amount which was equipped with the extinguishable capability on the molded transformer under combustion, and it was calculated with the Announcement of the Ministry of Government Administration and Home Affairs as the basis. With the injection of the calculated extinguishable chemicals, the ignited transformer has completely extinguished within one minute.

• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.438-441
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• 2012

Abalone shell is a high strength and light weighted ceramic composite material, which is composed of $CaCO_3$ platelet and protein. Microstructure of abalone shell has a matrix structure that is similar to the bricks and mortar. The technology inspired from nature which consumes low energy at low temperature is called bioinspired technology. In this study, to make high strength and light weighted ceramic composite materials using bioinspired technology, porous green body was prepared with $Al_2O_3$ platelet. PMMA was infiltrated into the porous green body, then warm pressed to eliminate pores present in the composite. The microstructure of the composite was observed with FESEM, and the mechanical/thermal properties were measured.

• Asian-Australasian Journal of Animal Sciences
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• v.17 no.10
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• pp.1434-1437
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• 2004

The study was conducted to evaluate the effects of montmorillonite anocomposite (MNC) on mercury residues in growing/finishing pigs. A total of 96 cross bred pigs ($Duroc{\times}Landrace{\times}large$ white, 48 barrows and gilts respectively), with similar initial weight (27.87${\pm}$1.15 kg), were used in this study. The animals were randomly assigned to two concentrations of mercury (0.1 and 0.3 ppm from $HgCl_2$) and two levels (0 and 0.3%) of MNC in a $2{\times}2$factorial arrangement of treatments. Each group has 3 pens (replications), and each pen has 8 pigs (4 barrows and 4 gilts). The experiment lasted for 90 days. The results showed that pig growth performances were not affected significantly by inclusion of Hg and addition of MNC (p$\geq$0.05). It indicated that the extent of intoxication in these pigs were not severe enough to impair growth performances. Both on the bases of 0.1 ppm and 0.3 ppm mercury supplementations, addition of 0.3% MNC markedly decreased mercury levels of blood, muscle, kidney and liver tissue (p<0.05). These results implied that the addition of non-nutritive sorptive material, MNC, could effectively reduce the gastrointestinal absorption of mercury via its specific adsorption, with a consequent reduction of mercury residues in body tissues. MNC had offered an encouraging solution to produce safe animal products with mercury contaminated feed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.672-678
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• 2020

Ogive parts of large-caliber ammunition in Korea are manufactured by the Press Nosing method, but this method has the disadvantage of requiring additional processes such as lubrication before and after the press process. This study proposes the possibility of applying the Swaging method to improve these shortcomings. A large-diameter shell body was manufactured in sub-scale and plastic working experiments using a swaging process were performed. We investigated whether plastic processing is possible up to 75 % of the diameter reduction rate that satisfies the final molding dimension, and whether the dimensions of the product produced by swaging molding are satisfactory as the hardness changes according to the diameter reduction rate and the increase in thickness. The test using the prototype confirmed that the hardness increased proportionally with the diameter reduction rate and by more than HV 335 at the reduction rate of 75 %. The material thickness variation tended to be similar to the theoretical calculated value, and the thickness increase rate was proportional to 65.4 % at the reduction rate of 75 %.

• Restorative Dentistry and Endodontics
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• v.44 no.4
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• pp.39.1-39.8
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• 2019

The present report presents a case of dens invaginatus (DI) in a patient with 4 maxillary incisors. A 24-year-old female complained of swelling of the maxillary left anterior region and discoloration of the maxillary left anterior tooth. The maxillary left lateral incisor (tooth #22) showed pulp necrosis and a chronic apical abscess, and a periapical X-ray demonstrated DI on bilateral maxillary central and lateral incisors. All teeth responded to a vitality test, except tooth #22. The anatomic form of tooth #22 was similar to that of tooth #12, and both teeth had lingual pits. In addition, panoramic and periapical X-rays demonstrated root canal calcification, such as pulp stones, in the maxillary canines, first and second premolars, and the mandibular incisors, canines, and first premolars bilaterally. The patient underwent root canal treatment of tooth #22 and non-vital tooth bleaching. After a temporary filling material was removed, the invaginated mass was removed using ultrasonic tips under an operating microscope. The working length was established, and the root canal was enlarged up to #50 apical size and obturated with gutta-percha and AH 26 sealer using the continuous wave of condensation technique. Finally, non-vital bleaching was performed, and the access cavity was filled with composite resin.

• Journal of Korean Dental Science
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• v.6 no.2
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• pp.50-57
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• 2013

Purpose: Autogenous tooth bone graft is proven to be efficient. We evaluated the bone healing effect and clinical capabilities of autogenous tooth bone materials as a scaffold when growth factor is used together with this material. Materials and Methods: Subjects were those who needed implant placement and bone graft because of missing tooth or alveolar bone defect and who kept their autogenous tooth or needed extraction of other tooth. Group I included autogenous tooth bone graft with growth factor, whereas Group II had only autogenous tooth bone graft. We investigated the bone healing state through computed tomography taken just before surgery and 3 to 4 months after surgery to evaluate the effectiveness of bone graft. Group I had 9 patients, whereas Group II had 5 patients. We compared the pre- and post-operative increase of the Hounsfield unit and bone height by analyzing the computed tomography images. Result: Sinus bone grafts numbered 8 cases, and vertical ridge augmentation was performed together with 3 cases of these. Vertical ridge augmentation was performed in 2 cases, and horizontal ridge augmentation in 1 case alone. Socket graft was done in 3 cases. The post-operative mean value of the Hounsfield unit was 960 in Group I and 836.7 in Group II, but the increase was almost similar, i.e., 636.9 in Group I and 634.7 in Group II on the average. Increase of bone height was 7.6 mm in Group I and 11.1 mm in Group II on the average. This difference was attributable to the fact that most of the cases were sinus bone graft in Group II. Conclusion: In this study, we suggest the possibility of autogenous tooth bone graft materials as a scaffold besides their bone healing ability.

• Bulletin of the Korean Chemical Society
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• v.25 no.4
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• pp.511-516
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• 2004

A Li$[Co_{0.17}Li_{0.28}Mn_{0.55}]O_2$ cathode compound was prepared by a simple combustion method. The X-ray diffraction pattern showed that this compound could be classified as ${\alpha} -NaFeO_2$ structure type with the lattice constants of a = 2.8405(9) ${\AA}$ and c = 14.228(4) ${\AA}$. According to XANES analysis, the oxidation state of Mn and Co ions in the compound were 4+ and 3+, respectively. During the first charge process, the irreversible voltage plateau at around 4.65 V was observed. The similar voltage-plateau was observed in the initial charge profile of other solid solution series between $Li_2MnO_3\;and\;LiMnO_2$ (M=Ni, Cr...). The first discharge capacity was 187 mAh/g and the second discharge capacity increased to 204 mAh/g. As the increase of cycling number, one smooth discharge profile was converted to two distinct sub-plateaus and the discharge capacity was slowly decreased. From the Co and Mn K-edge XANES spectra measured at different cyclic process, it can be concluded that irreversible transformation of phase is occurred during continuous cycling process.

• Bulletin of the Korean Chemical Society
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• v.26 no.5
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• pp.740-746
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• 2005

In this article, we report the tandem mass spectrometry investigations for the electron capture efficiencies of the protons belonging to the different locations (generations) in a poly(propylene imine) dendrimer with three layers of a repeat unit (named as the third generation dendrimer). The employed tandem mass spectrometry methods include SORI-CAD (sustained off-resonance irradiation collisional activation dissociation) and ECD(electron capture dissociation) mass spectrometry. We obtained SORI-CAD spectra for the dendrimer ions in the different charge states, ranging from 2+ to 4+. The analysis of fragmentation sites provides the information as to where the protons are distributed among various generations of the dendrimer. Based upon this, a new strategy to study the electron capture efficiencies of the protons is utilized to examine a new type of triplycharged ions by SORI-CAD, i.e., the 3+ ions generated from the charge reduction of the native 4+ ions by ECD: (M+4H)$^{4+}\;+\;e^-\;{\rightarrow}$ (M+4H)$^{3+\bullet}$ ${\rightarrow}\;({H^{\bullet}}_{ejected}$) + (M+3H)$^{3+}\;\rightarrow$ CAD. Interestingly, comparison of these four SORICAD spectra indicates that the proton distribution in the charge-reduced 3+ ions is very close to that in the native 4+ ions. It further suggests that in this synthetic polymer ($\sim$1.7 kDa) with an artificial architecture, the electron capture efficiencies of the protons are actually insensitive to where they are located in the molecule. This is somewhat contradictory to common expectations that the protons in the inner generations may not be well exposed to the incoming electron irradiation as much as the outer ones are, thus may be less efficient for electron capture. This finding may carry some implications for the case of medium sized peptide ions with similar masses, which are known to show no obvious site-specific fragmentations in ECD MS.