• Journal of the Korean Society of Safety
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• v.38 no.6
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• pp.1-8
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• 2023

The health state of the oil transformer is evaluated by the age of use and the state of internal defects. Mineral Oil, used as an insulator for oil transformers, creates specific gases and compounds through chemical reactions caused by heat, moisture, and partial discharge inside the transformer. It is possible to determine the aging and defect of the transformer through these gases and compounds. So, it is an important indicator to evaluate the health of a transformer. In this study, factors for assessing the health of transformers were hierarchically categorized, and key factors for each hierarchy were selected for design weighting. These weights were determined through surveys conducted with experts in the fields of transformer design, operation, and quality. For the health of a transformer, defect-related factors are approximately three times more important than factors related to aging. Additionally, defect-related factors showed a higher weighting for gases generated at high temperatures. Furthermore, Furan was determined to have a high weight, directly associated with insulating paper aging. Based on these findings, a health index was proposed, and a comparative analysis was conducted by categorizing 40 operational transformers into normal and comparison groups to evaluate and validate it.

• Polymer(Korea)
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• v.36 no.3
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• pp.321-325
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• 2012

In this work, we prepared the activated graphite nanofibers (A-GNFs) via chemical activation with KOH/GNFs ratios in a range of 0 to 5. The effect of KOH activation was studied in the surface and pore properties of the samples for electrochemical performance. The surface properties of A-GNFs were characterized by XRD and SEM measurements. The textural properties of the A-GNFs were investigated by $N_2$/77 K adsorption isotherms using Brunauer-Emmett-Teller (BET) equation. Their electrochemical behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge performance. From the results, electrochemical performances of the A-GNFs were improved with increasing the ratio of KOH reagent. It was found that specific surface area and total pore volume of the A-GNFs were increased by KOH activation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.378-379
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• 2006

The carbon thin film was developed by the CVD method using the carbon source of toluene with the stream of argon gas at $800{\sim}1100^{\circ}C$ for 1 hour. Developed carbon thin films have the material loading of 0.27 mg($800^{\circ}C$), 0.80 mg($900^{\circ}C$), 2.3 mg($1000^{\circ}C$), and 2.9 mg($1100^{\circ}C$) for the disk of 15 mm diameter on single side. The characteristics of carbon thin film as the anode of thin film battery were evaluated using Li|C coin cell. Li|C($1100^{\circ}C$) coin cell has the first specific discharge and charge capacity of 953 mAh/g and 374 mAh/g, respectively, resulting the first Ah efficiency of 39.3 %. Capacity retention of the 5th cycle was 93.2 % indicating good cycleability. The carbon thin film prepared by CVD shows good specific capacity and cycleability, but low Ah efficiency.

• Journal of the Korean institute of surface engineering
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• v.56 no.5
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• pp.299-308
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• 2023

In this study, phosphorus (P)-doped nickel cobaltite (P-NiCo₂O₄) and nickel-cobalt layered double hydroxide (P-NiCo-LDH) were synthesized on nickel (Ni) foam as a conductive support using hydrothermal synthesis. The thermal properties, crystal structure, microscopic surface morphology, chemical distribution, electronic state of the constituent elements on the sample surface, and electrical properties of the synthesized P-NiCo₂O₄ and P-NiCo-LDH samples were analyzed using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The P-NiCo₂O₄ electrode exhibited a specific capacitance of 1,129 Fg^-1 at a current density of 1 Ag^-1, while the P-NiCo-LDH electrode displayed a specific capacitance of 1,012 Fg^-1 at a current density of 1 Ag-1. When assessing capacity changes for 3,000 cycles, the P-NiCo₂O₄ electrode exhibited a capacity retention rate of 54%, whereas the P-NiCo-LDH electrode showed a capacity retention rate of 57%.

• Journal of Digital Contents Society
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• v.18 no.6
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• pp.1199-1205
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• 2017

Global energy consumption is rapidly increasing yearly due to drastic industrial advances, requiring the development of new energy storage devices. For this reason, supercapacitors with fast charge-discharge, long life cycle and high power density is getting attention, and have been considered as one of the potential energy storage systems. In this research, we developed a supercapacitor that consists of amorphous manganese oxide($MnO_2$) electrodes deposited onto carbon cloth substrates using the hydrothermal method. The Fe-doped amorphous $MnO_2$ samples were characterized by X-ray diffraction(XRD), Energy Dispersive X-ray spectroscopy(EDX), as well as scanning electron microscopy(SEM). The electrochemical analysis of the prepared samples were performed using cyclic voltammetry and galvanostatic charge-discharge measurements in 1M $Na_2SO_4$ electrolyte. The test results demonstrate that the supercapacitor based on the Fe-doped amorphous $MnO_2$ electrodes has a specific capacitance as high as 163F/g at 1A/g current density, and good cycling stability of 87.34% capacitance retention up to 1000 cycles.

• Child Health Nursing Research
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• v.4 no.2
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• pp.159-176
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• 1998

In effort to conduct comparative study on the caregiving environment of Neonatal Intensive Care Unit(NICU) in both U. S and Korea, this study was been conducted first in the U.S. Purpose : The purpose of this study is to identify the physical environment and direct caregiving practices to lowbirth weight infants in NICU in the US. It also aims to examine the NICU outcome status and behavioral reponses of lowbirth weight infants. Methods : A study design using descriptive and inferential statistics was been conducted through an observational, field method. A sample of 15 preform infants admitted to NICU were recruited for the study. The subjects were those with birth weight between 1,000 gm to 1,500 gm, born at the gestation period of 27 to 33 weeks, and without any chromosomal or other genetic anomalies, major congenital infections, or maternal illness. Thirty minutes observation(three times of ten minutes of continuous observation)of the infant's behavior and physiological status, and an four-hour observation of the physical environment and direct care giving procedures were been conducted on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. The data to be collected were in four areas : the demograghic characteristics of the infants, the physical environment and care giving procedures, the frequency of the infant's designated behavior and physiological response, and NICU outcome variables. A descriptive analysis and Kruskal-Wallis, Pearson r were been applied according to variable characteristics. Results : 1. Mother's mean age was 29.47. The sample consisted of 6 males and 9 females. Mean gestational ages were 29.17 weeks. Mean birth weight was 1236.33g. Mean Apgar scores at one minute were 6.6, and 7.8 at five minutes. 2. The location for the incubator was in the distance from the light, X-ray screens and nursing station, in proximity to side-lamp, telephone and faucet on the third day after birth. The location for the incubator was in the distance from the light and radio on the tenth day and in proximity to nursing station on the day of dischage from the NICU or at 34weeks postconception. 3. Nesting was the most applying aids to the infants. And foot roll, shielding and plastic frame were frequently using by nurses for facilitating well modulated restful posture. 4. There were statistically significant changes in the patterns of physical environment included locating the infant's incubator and bedding, specific aids to self regulation on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. 5. Statistically significant changes were not appeared in the patterns of direct caregiving procedure to the infants included stress inducing or reducing manipulations on the 3rd and 10th day after birth, and on the day of discharge from the NICU or at 34weeks postconception. 6. The stress response of the infants in NICU were significantly reduced as the infants grow older. 7. There were not statistically significant correlation between the physical envronment and the stress responses of the infants in NICU. 8. There were statistically significant correlation between the direct caregiving procedure to the infants and the stress response of the infants in NICU in the second and third observation on the day three. 9. Average weight gain per day from birth to discharge was 38.73g, number of days in the hospital was 42.60, number of days before bottle feeding was 3.6. Postconception age starting bottle feed ing was 31/sup +5/ weeks. Number of days on mechanical ventilator was average 7.64, 11.42 was an average number of days of oxygen need. Conclusion : It, thus, appears that to minimize the sensorymotor stimulation for the low birthweight preterm infant in NICU, manipulation of care giving practices to the babies whatever the stress inducing or reducing procedures, have to be limited in the immediate early stage after birth. And it needed to be reexamine to identify the appropriate and specific physical environment and the patterns of direct caregiving to the low birthweight preform infant as the infants grow older in NICU.

• Magazine of the Korean Society of Agricultural Engineers
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• v.17 no.1
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• pp.3642-3654
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• 1975

The purpose of this thesis is to derive a unit hydrograph which may be applied to the ungaged watershed area from the relations between directly measurable unitgraph properties such as peak discharge(qp), time to peak discharge (Tp), and lag time (Lg) and watershed characteristics such as river length(L) from the given station to the upstream limits of the watershed area in km, river length from station to centroid of gravity of the watershed area in km (Lca), and main stream slope in meter per km (S). Other procedure based on routing a time-area diagram through catchment storage named Instantaneous Unit Hydrograph(IUH). Dimensionless unitgraph also analysed in brief. The basic data (1969 to 1973) used in these studies are 9 recording level gages and rating curves, 41 rain gages and pluviographs, and 40 observed unitgraphs through the 9 sub watersheds in Nak Oong River basin. The results summarized in these studies are as follows; 1. Time in hour from start of rise to peak rate (Tp) generally occured at the position of 0.3Tb (time base of hydrograph) with some indication of higher values for larger watershed. The base flow is comparelatively higher than the other small watershed area. 2. Te losses from rainfall were divided into initial loss and continuing loss. Initial loss may be defined as that portion of storm rainfall which is intercepted by vegetation, held in deppression storage or infiltrated at a high rate early in the storm and continuing loss is defined as the loss which continues at a constant rate throughout the duration of the storm after the initial loss has been satisfied. Tis continuing loss approximates the nearly constant rate of infiltration (${\Phi}$-index method). The loss rate from this analysis was estimated 50 Per cent to the rainfall excess approximately during the surface runoff occured. 3. Stream slope seems approximate, as is usual, to consider the mainstreamonly, not giving any specific consideration to tributary. It is desirable to develop a single measure of slope that is representative of the who1e stream. The mean slope of channel increment in 1 meter per 200 meters and 1 meter per 1400 meters were defined at Gazang and Jindong respectively. It is considered that the slopes are low slightly in the light of other river studies. Flood concentration rate might slightly be low in the Nak Dong river basin. 4. It found that the watershed lag (Lg, hrs) could be expressed by Lg=0.253 (L.Lca)0.4171 The product L.Lca is a measure of the size and shape of the watershed. For the logarithms, the correlation coefficient for Lg was 0.97 which defined that Lg is closely related with the watershed characteristics, L and Lca. 5. Expression for basin might be expected to take form containing theslope as {{{{ { L}_{g }=0.545 {( { L. { L}_{ca } } over { SQRT {s} } ) }^{0.346 } }}}} For the logarithms, the correlation coefficient for Lg was 0.97 which defined that Lg is closely related with the basin characteristics too. It should be needed to take care of analysis which relating to the mean slopes 6. Peak discharge per unit area of unitgraph for standard duration tr, ㎥/sec/$\textrm{km}^2$, was given by qp=10-0.52-0.0184Lg with a indication of lower values for watershed contrary to the higher lag time. For the logarithms, the correlation coefficient qp was 0.998 which defined high sign ificance. The peak discharge of the unitgraph for an area could therefore be expected to take the from Qp=qp. A(㎥/sec). 7. Using the unitgraph parameter Lg, the base length of the unitgraph, in days, was adopted as {{{{ {T}_{b } =0.73+2.073( { { L}_{g } } over {24 } )}}}} with high significant correlation coefficient, 0.92. The constant of the above equation are fixed by the procedure used to separate base flow from direct runoff. 8. The width W75 of the unitgraph at discharge equal to 75 per cent of the peak discharge, in hours and the width W50 at discharge equal to 50 Per cent of the peak discharge in hours, can be estimated from {{{{ { W}_{75 }= { 1.61} over { { q}_{b } ^{1.05 } } }}}} and {{{{ { W}_{50 }= { 2.5} over { { q}_{b } ^{1.05 } } }}}} respectively. This provides supplementary guide for sketching the unitgraph. 9. Above equations define the three factors necessary to construct the unitgraph for duration tr. For the duration tR, the lag is LgR=Lg+0.2(tR-tr) and this modified lag, LgRis used in qp and Tb It the tr happens to be equal to or close to tR, further assume qpR=qp. 10. Triangular hydrograph is a dimensionless unitgraph prepared from the 40 unitgraphs. The equation is shown as {{{{ { q}_{p } = { K.A.Q} over { { T}_{p } } }}}} or {{{{ { q}_{p } = { 0.21A.Q} over { { T}_{p } } }}}} The constant 0.21 is defined to Nak Dong River basin. 11. The base length of the time-area diagram for the IUH routing is {{{{C=0.9 {( { L. { L}_{ca } } over { SQRT { s} } ) }^{1/3 } }}}}. Correlation coefficient for C was 0.983 which defined a high significance. The base length of the T-AD was set to equal the time from the midpoint of rain fall excess to the point of contraflexure. The constant K, derived in this studies is K=8.32+0.0213 {{{{ { L} over { SQRT { s} } }}}} with correlation coefficient, 0.964. 12. In the light of the results analysed in these studies, average errors in the peak discharge of the Synthetic unitgraph, Triangular unitgraph, and IUH were estimated as 2.2, 7.7 and 6.4 per cent respectively to the peak of observed average unitgraph. Each ordinate of the Synthetic unitgraph was approached closely to the observed one.

• Clean Technology
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• v.18 no.2
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• pp.177-182
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• 2012

Mesoporous anatase $TiO_2$ nanoparticles have been synthesized by a hydrothermal method using a tri-block copolymer as a soft template. The resulting $TiO_2$ materials have a high specific surface area of $230\;m^2/g$, a predominant pore size of 6.8 nm and a pore volume of 0.404 mL/g. The electrochemical properties of mesoporous anatase $TiO_2$ for lithium ion battery (LIB) anode materials have been investigated by typical coin cell tests. The initial discharge capacity of these materials is 240 mAh/g, significantly higher than the theoretical capacity (175 mAh/g) of LTO ($Li_4Ti_5O_{12}$). Although the discharge capacity decreases with the C-rate increase, the mesoporous $TiO_2$ is very promising for LIB anode because the surface for the Li insertion is presented significantly with mesopores. Nitrogen doping has a certain effect to control the capacity decrease by improving the electron transport in $TiO_2$ framework.

• Korean Journal of Materials Research
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• v.18 no.9
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• pp.457-462
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• 2008

Through the electrostatic interaction between the poly-diallydimethylammonium chloride (PDDA) modified Multi-walled carbon nanotube (MWNT) and $SnO_2$ suspension in 1mM $NaNo_3$ solution, MWNT-$SnO_2$ nanocomposites (MSC) for anode electrodes of a Li-ion battery were successfully fabricated by colloidal heterocoagulation method. TEM observation showed that most of the $SnO_2$ nanoparticles were uniformly deposited on the outside surface of the MWNT. Galvanostatic charge/discharge cycling tests showed that MSC anodes exhibited higher specific capacities than bare MWNT and better cyclability than unsupported nano-$SnO_2$ anodes. Also, after 20 cycles, the MSC anode fabricated by heterocoagulation method showed more stable cycle properties than the simply mixed MSC anode. These improved electrochemical properties are attributed to the MWNT, which adsorbs the mechanical stress induced from volume change and increasing electrical conductivity of the MSC anode, and suppresses the aggregation between the $SnO_2$ nanoparticles.

• Journal of the Ergonomics Society of Korea
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• v.31 no.3
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• pp.421-426
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• 2012

As headlamp technology advances, newly developed various headlamps were introduced in the market. The objective of this study is to quantitatively analyze the detection distance of the recently developed LED headlamps and existing headlamps, complying with specific technical standard. Background: The detection distance of headlamps is very important to prevent automobile accident at night time. The studies of detection distance of LED, Halogen and HID headlamp have been conducted, but no study has shown the detection distance of pedestrian target with various colors (Black, White, Blue). Method: The experiment of detection distance was conducted with 30 people, which divide into 2 groups as 15 men and 15 women. Automatic transferable target on the rail was manufactured in order to reduce the error of study's result, and ANOVA also conducted to analyze the main effect with sign color, sex and headlamp classified by detection distance. In addition, the luminance by average detection distance was measured as well. Results: The detection distance of headlamps was HID > LED > Halogen. The luminance measure of LED headlamp was lower than HID and Halogen headlamps. Conclusion: The headlamp performs a very significant role for safety at night time but it needs to be improved through assessment of visual characteristics. Also, it needs to be suggested the need of test method for dynamic detection distance concerning technical development is suggested.