• 전기의세계
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• v.28 no.4
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• pp.53-63
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• 1979

Interface recombination velocity in $Al_{x}$G $a_{1-x}$ As-GaAs and $Al_{0.85}$, G $a_{0.15}$ As-GaA $s_{1-y}$S $b_{y}$ heterojunction systems is studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n $Al_{x}$G $a_{1-x}$ As-GaA $s_{1-y}$S $b_{y}$-A $l_{x}$G $a_{1-x}$ As double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAs Sb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates. In the AlGaAs system, elastic lattice deformation with effective Poisson ratios .mu.$_{eff}$ (100=0.312 and .mu.$_{eff}$ (111B) =0.190 was observed. The lattice constant $a_{0}$ (A $l_{x}$G $a_{1-x}$ As)=5.6532+0.0084x.angs. was obtained at 300K which is in good Agreement with Vegard's law. In the GaAsSb system, although elastic lattice deformation was observed in (111) B-oriented crystals, misfit dislocations reduced the Poisson ratio to zero in (100)-oriented samples. When $a_{0}$ (GaSb)=6.0959 .angs. was assumed at 300K, both (100) and (111)B oriented GaAsSb layers deviated only slightly from Vegard's law. Both (100) and (111)B zero-mismatch $Al_{0.85}$ G $a_{0.15}$As-GaA $s_{1-y}$S $b_{y}$ layers were grown from melts with a weight ratio of $W_{sb}$ / $W_{Ga}$ =0.13 and a growth temperature of 840 to 820 .deg.C. The corresponding Sb compositions were y=0.015 and 0.024 on (100) and (111)B orientations, respectively. This occurs because of a fortuitous in the Sb distribution coefficient with orientation. Interface recombination velocity was estimated from the dependence of the effective minority carrier lifetime on double-heterojunction spacing, using either optical phase-shift or electroluminescence timedecay techniques. The recombination velocity at a (100) interface was reduced from (2 to 3)*10$^{4}$ for y=0 to (6 to 7)*10$^{3}$ cm/sec for lattice-matched $Al_{0.85}$G $a_{0.15}$As-GaA $s_{0.985}$S $b_{0.015}$ Although this reduction is slightly less than that expected from the exponential relationship between interface recombination velocity and lattice mismatch as found in the AlGaAs-GaAs system, solar cells constructed from such a combination of materials should have an excellent spectral response to photons with energies over the full range from 1.4 to 2.6 eV. Similar measurements on a (111) B oriented lattice-matched heterojunction produced some-what larger interface recombination velocities.ities.ities.s.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.3011-3015
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• 2009

Structural and thermo-analytical studies were carried out to understand the phase formation kinetics of the single phase $Bi_5Ti_3FeO_{15}$ (BTFO) nanocrystals in $Bi_2O_3-Fe_2O_3-TiO_2$, during the polymerized complex (PC) synthesis method. The crystallization of Aurivillius phase $Bi_5Ti_3FeO_{15}$ layered perovskite was found to be initiated and achieved under the temperature conditions in the range of ${\sim}$800 to 1050$^{\circ}C$. The activation energy for grain growth of $Bi_5Ti_3FeO_{15}$ nanocrystals (NCs) was very low in case of NCs formed by PC (2.61 kJ/mol) than that formed by the solid state reaction (SSR) method (10.9 kJ/mol). The energy involved in the phase transformation of Aurivillius phase $Bi_5Ti_3FeO_{15}$ from $Bi_2O_3-Fe_2O_3-TiO_2$ system was ${\sim}$ 69.8 kJ/mol. The formation kinetics study of $Bi_5Ti_3FeO_{15}$ synthesized by SSR and PC methods would not only render a large impact in the nanocrystalline material development but also in achieving highly efficient visible photocatalysts.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.5
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• pp.11-21
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• 2007

Currently in the country, the necessity of seismic analyses is increasing due to the increase of demand and interest in seismic design. Especially, shear wall apartments are constructed mostly for a residental building so seismic analyses for the apartment are actively executed. For the seismic analysis of the shear wall apartment, it may be not efficient in time and effort to model the entire structure by a finite element mesh. Therefore, an equivalent model is needed to simulate the dynamic behavior of the structure by decreasing the number of degrees of freedom. In this study, a method to form an equivalent model that is simple and easy to use was proposed utilizing effective mass coefficient that is highly correlated to mode shape of the structure. This equivalent model was obtained by replacing a shear wall structure with an equivalent frame structure having beams and columns. This model can be used very effectively when excessive seismic analyses are necessary in a short period because it can be operated in any commercial program and reduce the analysis time. Also, it can model floor slabs so it can represent the actual behavior of shear wall apartments. Furthermore, it is very excellent since it can represent the asymmetry of the structure.

• Journal of East-West Nursing Research
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• v.8 no.1
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• pp.103-112
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• 2003

This paper focused on providing the groundwork for the development of proper nursing interventions to enhance the quality of life for the elderly by identifying the factors that may affect their health beliefs and behaviors. A survey was conducted on a group of people aged between 60 and 86 years residing in S and K cities from January to March of 2003, who agreed to participate in the research. Data was collected using instruments measuring health beliefs and health behaviors, and was analyzed by using SPSS. The results of this study are as follow. 1) Those in the group were aged between60 and 86 years, and the average age was 66.94 years old. Most of them were living together with their spouses. From the survey, 83.5% replied "above average" on the question regarding their current health condition, whereas, 46.0% mentioned that they had some sort of diseases. 2) Overall average score of the health belief was 516.05, with a mean $3.71{\pm}4.07$. This indicates that the studied group held a high level of health belief, which affects their attitude and intention to lead a healthy life by placing the present life under control in harmony with nature. 3) Overall average score of the health behaviors was 392.24 with a mean $2.82{\pm}.52$. For health purposes, the behaviors that the elderly people were taking were mostly static ones requiring a low level of activity. The analysis showed that they generally were involved in self-trained, individualized health care. Thus, the elderly place a higher priority on regular dietary behaviors than on physical activity. 4) The correlation between health belief, a cognitive aspect on health, and health behaviors, a behavioral aspect showed a very high linear relationship (r=.520, p<.000). Consequently, it is found that those who have higher cognitive health belief are involved in higher level of behavioral health practice. These findings concluded that the Korean elderly have good health beliefs, well controlling their minds and being harmonious with nature. Health behaviors that they are engaged in are mostly static, requiring low level activity, while they place higher priority on regular dietary habits and conducting self-trained individualized health care. Important factor affecting their health beliefs and health behaviors was found to be their health practice. Since higher health belief is highly related with good health behaviors, development of health activity programs is in need as a means for an efficient health improvement, where motivating environment may be established to enhance the health belief of the elderly and to satisfy individual values.

• Journal of the Korea Society of Computer and Information
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• v.16 no.11
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• pp.85-93
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• 2011

The music education improves the creative talent, social skills and academic achievement of the students. For the efficient music education, the learner centered study is highly recommended rather than the passive education, which supports self-control in selecting teaching materials, learning patterns and speed. For the successful self learning, it is requested to develop the collaborative educational learning tools, especially electronic collaborators such as H/W and S/W. Though there exist many commercialized electronic instruments and the PC MIDI based softwares, these tools have some limits and problems for the primary student to learn playing the musical instrument by himself. In this paper, we propose a supporting tool implementation method using an electronic keyboard instrument with USB Interface and PC-based software to help the primary student to learn playing the musical instrument. We implemented an electronic keyboard instrument module compactly and at low cost using a PIC18F4550 MCU. PC based software was developed to edit musical score, process the MIDI information, and interact with the electronic keyboard instrument module. This tool can offer a similar keyboard instrument environment and can be incorporated with self learning contents.

• Journal of Digital Convergence
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• v.15 no.2
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• pp.135-144
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• 2017

This study is to identify the growth rate and volatility of logistics related firms in the stock market. To do this, we used monthly data for 197 years from June 2000 to October 2016 by selecting KOSPI and Transport & Storage(T&S), KOSDAQ, Transportation(TRANS) index. The purpose of this study is to compare the T&S and TRANS stock index returns with the KOSPI and KOSDAQ index. And we are to judge whether the development potential of the logistics industry and the value of the investment of related companies in the future is high. For this purpose, we will analyze the basic statistics, correlation and growth rate of each index, and compare T&S and TRANS with market returns. Analysis result, for the past 197 months logistics related T&S and TRANS have been higher than market returns. The correlation was highly related to TRANS and T & S in KOSPI, but it was not related to KOSDAQ. TRANS represents high risk and high return, while KOSDAQ represents high risk and low return market. TRANS is considered to be an efficient investment. We expect the future development of logistics related industries and T & S and TRANS to show a high rate of increase compared to the market returns.

• Journal of Digital Convergence
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• v.18 no.4
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• pp.403-409
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• 2020

Gamification can be more fun and interesting than boring and it can be used for variety of educational subjects. Through the fun and flow of the learner, the learner understands the meaning and context of the problem to be solved. It will be able to collect, analyze and creatively solve data in a way that computers understand. Training through gamification will be an effective and memorable coding education for the efficient learning of coding education among the newly designated compulsory education. It is considered to be highly useful as a convergence study to increase tourism experience. Currently, in the field of school, coding education is mainly conducted using entry and scratch, which are educational programming languages, and coding education using gamification is not extensively used in the current education field. It is also expected to be used to increase the tourism experience, and it can be used to enhance the learner's computational thinking ability and creativity.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.11-15
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• 2017

As the heat dissipation problem is increased in 3D multi flip chip packages, an improvement of thermal conductivity in bonding interfaces is required. In this study, the effect of alumina filler addition was investigated in non-conductive paste(NCP). The fine alumina filler having average particles size of 400 nm for the fine pitch interconnection was used. As the alumina filler content was increased from 0 to 60 wt%, the thermal conductivity of the cured product was increased up to 0.654 W/mK at 60 wt%. It was higher value than 0.501 W/mK which was reported for the same amount of silica. It was also found out that the addition of fine sized alumina filler resulted in the smaller decrease in thermal conductivity than the larger sized particles. The viscosity of NCP with alumina addition was increased sharply at the level of 40 wt%. It was due to the increase of the interaction between the filler particles according to the finer particle size. In order to achieve the appropriate viscosity and excellent thermal conductivity with fine alumina fillers, the highly efficient dispersion process was considered to be important.

• Korean Journal of Soil Science and Fertilizer
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• v.50 no.5
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• pp.345-356
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• 2017

We investigated 52 livestock farming complexes in Gyeong-Gi and Incheon provinces based on low, medium, and high livestock density and groundwater quality. The objective of this study was to evaluate a relationship between nitrate N concentration in groundwater and animal factors, such as livestock density and animal species. 2,200 groundwater samples for 3 years from 2012 to 2014 at Gyeong-Gi and Incheon provinces were collected and analyzed for pH, EC, DO, ORP, temperature, major anions and cations, such as $NO_3-N$, ${HCO_3}^-$, ${PO_4}^-$, ${SO_4}^{2-}$, $Cl^-$, $NH_4-N$, $K^+$, $Na^+$, $Ca^{2+}$, $Mg^{2+}$, T-N, and TOC. Average concentration of total N for generated load density was $23,973g\;day^{-1}\;km^{-2}$ for cattle, $51,551g\;day^{-1}\;km^{-2}$ for pig, and $52,100g\;day^{-1}\;km^{-2}$ for poultry. For animal feeding species, average ratio for generated load over discharge load was 16.1% for cattle, 7.8% for pig, and 7.1% for poultry. Therefore, cattle feeding region is highly vulnerable for water pollution compared to pig and poultry feeding areas. The concentrations of chloride, nitrate, and total N in the groundwater samples were higher at high animal farming regions than other regions. The average concentration of nitrate, and chloride in groundwater samples was $5.0mg\;L^{-1}$, $16.6mg\;L^{-1}$ for low livestock density, $6.9mg\;L^{-1}$, $17.7mg\;L^{-1}$ for medium livestock density and $7.6mg\;L^{-1}$, $22.7mg\;L^{-1}$ for high livestock density and total nitrogen (T-N) was $7.7mg\;L^{-1}$ for low livestock density, $9.4mg\;L^{-1}$ for medium livestock density, $10.7mg\;L^{-1}$ for high livestock density. In conclusion, based on this research, for managing groundwater quality near livestock farming regions, $Ca-(Cl+NO_3)$ group from the Piper diagram is more efficient than using 19 factors for water quality standard.

• Journal of Wetlands Research
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• v.17 no.4
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• pp.414-420
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• 2015

Nitrogen is one of main causes to induce eutrophication of water system and one of contaminants that must be treated for protection of water system. In this study, it was intended to identify a method to increase operation efficiency of municipal wastewater treatment plant (MWTP) by treating high concentration nitrogen. A laboratory scale reactor was operated by using sludge thickener supernatant in the MWTP. During operation of the laboratory scale reactor, it was intended to induce stable nitritation and analyze effects of related operation factors. As results, it was shown that the nitiritation could be induced artificially through control of retention time and sections where the stable nitiritation was induced were identified also. In particular, highly efficient nitrite conversion efficiency near 90% was identified in condition of 1 day retention time. Especially, it was shown that ammonium nitrogen load affected ammonium nitrogen removal efficiency and nitrite conversion efficiency. In the condition of high ammonium nitrogen load, the nitrite conversion efficiency and the ammonium nitrogen removal efficiency decreased. On the contrary in the condition of low ammonium nitrogen load, it was found that the nitrite conversion efficiency decreased. It means that control of ammonium nitrogen concentration and its retention time is needed for the nitritation. It is considered that for the sewage containing high load nitrogen in sludge treatment process as like the sludge thickener supernatant, the nitritation can be applied, which can be suggested as a modification method of MWTP.