• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.319-319
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• 2011

Hydrolysis of sodium borohydride provides a safe and clean approach to hydrogen generation. Having the proper catalytic support for controlling this reaction is therefore a valuable technology. Here we demonstrate the capability of hydroxyapatite as a novel catalytic support material for hydrogen generation. Aside from being inexpensive and durable, we reveal that Ru ion exchange on the HAP surface provides a highly active support for sodium borohydride hydrolysis, exemplifying a high total turnover number of nearly 24,000 mol $H_2$/ mol Ru. Moreover, we observe that the RuHAP support exhibits a high catalytic lifetime of approximately one month upon repeated exposure to $NaBH_4$ solutions. In addition to examining surface area effects, we also identified the role of complex surface morphology in enhancing hydrolysis by the catalytic transition metal covered surface. Particularly, we found that a polycrystalline RuHAP catalytic support exhibits shorter induction times for the initial bubble formation as well as increased hydrogen generation rates as compared to a single crystal supports. The independent factor of a complex surface morphology is believed to provide enhanced sites for gas release during the initial stages of the reaction. By demonstrating the ability to shorten induction time and enhance catalytic activity through changes in surface morphology and Ru content, we find it feasible to further explore this catalyst support in the construction of a practical hydrogen generator.

• 한국자동차공학회논문집
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• 제19권6호
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• pp.140-147
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• 2011

The injection nozzle of an electro-hydraulic injector for the common rail Diesel fuel injection system is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the slenoid actuator was considered as a prime movers in high pressure Diesel injector. Namely a solenoid-driven Diesel injector with different driving current types, as a general method driven by solenoid coil energy, has been applied with a purpose to develop the analysis model of the solenoid actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code. Aimed at simulating the hydraulic behavior of the solenoid-driven injector, the circuit model has been developed as a unified approach to mechanical modeling in this study. As this analytic results, we know the suction force and first order time lag for driving force can be endowed in solenoid-driven injector in controlling the injection rate. Also it can predict that the input current wave exerted on solenoid coil is the dominant factor which affects on the initial needle behavior of solenoid-driven injector than the hydraulic force generated by the constant injection pressure.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.81-89
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• 2009

In this experimental study, the effects of clean alternative fuels compatible with diesel combustion on nano-sized particle emission characteristics were investigated in a 0.5L auto-ignited single-cylinder engine with a compression ratio of 15. Because the number concentration of nano-sized particles emitted by automotive engine, that are suspected of being hazardous to human health and environment, might increase with engine fuel considerably and recently attracted attention. So a ultra-low sulfur diesel(ULSD), BD100(100% bio-diesel) and Di-Methyl Ether(DME) fuels used for this study. And, as a particle measuring instrument, a fast-response particle spectrometer (DMS 500) with heated sample line was used for continuous measurement of the particle size and number distribution in the size range of 5 to 1000nm (aerodynamic diameter). As this research results, we found that this measurements involving the large proportion of particles under size order of 300nm and number concentration of $4{\times}10^9$ allowed a single or bi-modal distribution to be found at different engine load conditions. Also the influence of oxygen content in fuel and the catalyst could be a dominant factor in controlling the nano-sized particle emissions in auto-ignited engine.

• 화약ㆍ발파
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• 제27권2호
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• pp.1-11
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• 2009

본 연구에서는 프리스플리팅 적용 시 심발 발파를 통해 먼저 자유면을 확보한 후 이에 따른 응력변화를 관찰함으로서 최 외곽영역에서 균열형성을 함에 있어서의 유리함을 판단하고자 하며 균열형성이 용이한 조건을 찾고자 한다. 수치해석에서는 터널 내 최소주응력 방향을 고려했으며 수치해석 결과 응력의 방향변화는 가압하중의 크기변화에 큰 영향이 있음을 확인할 수 있었고, 차응력이 증가할수록 균열이 증가하는 경향을 확인하였다. 모형실험결과 응력장을 고려한 프리스플리팅공법 적용으로 기존 프리스플리팅 공법에 비해 균열 제어가 용이하고, 이를 통해 이완영역 축소를 기대할 수 있으며 또한 새로운 개념의 프리스플리팅 공법의 적용성을 판단하였다.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.1-7
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• 2001

This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.

• 대한공간정보학회지
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• 제20권4호
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• pp.19-27
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• 2012

RUSLE는 강우침식, 토양침식, 지형적 특징, 경작관리 등과 같은 유역 토양유실량 산정에 널리 사용되어 왔다. RUSLE 관련 매개변수 중 강우침식인자는 가장 민감도가 큰 요소로 그 신뢰성을 높이는 것은 정확한 유역 토양유식량 산정을 위한 필수조건이다. 국내에서는 유역의 토양침식을 조절하고 토양유실량 산정을 위한 강우침식인자 산정에 대한 명확한 기준이 마련되어 있지 않고 연평균 강우량과 침식인자의 관계식을 이용하거나 TRB에서 제안한 방법을 이용하고 있다. 본 연구에서는 빈도분석을 이용하여 강우침식인자를 산정하는 절차를 제안하였다. 다양한 재현빈도와 지속기간에 대해 계산된 강우침식인자는 지속시간에 따라 정규분포 형태로 나타났기 때문에 확률분포함수를 이용해서 강우침식인자를 산정할 수 있도록 적합분포함수를 제안하였다. 본 연구에서 제안한 방법을 통하여 유역의 토양유식을 효과적으로 조절하고 구조물에 대한 설계토양유실량을 계산하기 위한 최적의 강우침식인자를 산정할 수 있을 것으로 사료된다.

• 한국병원경영학회지
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• 제5권2호
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• pp.40-58
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• 2000

Nurses are medical personnel, who play a key role in supporting patient care, so it is important to supply them adequately in balance with ever increasing medical demand. But there appears severe shortage of nurses in some hospitals because of their uneven distribution, especially in small sized-hospitals and rural-hospitals. As nationwide distorted distribution of nurses in Korea is just like what monopsony model(a kind of market structure model) tells us, it is attempted to explain this situation of nurse labor market in Korea on the basis of monopsony model and presented in this paper. Specifically, determinants of nurse wage and the level of their relative employment were examined, and monopsony impact on their wage and the level of relative employment controlling those determinants were studied. Major results of this study arc as follows. The most important determinant of nurse wage level in this study was the wage level of a local community where each hospital located Hospital owner's characteristics an educational function of each hospital were also important factors. With these factor controlled, it was found that monopsony power of each hospital was negativel associated with nurse wage level as expected. 1% increase in monopsony power of hospital(measured by Herfindah-Hirschman Index) reduced nurse wage by $5,674{\sim}19,19$ won(in Korean currency). With regard to the level of relative employment, the most important determinant wa the capacity for supplying nurses of the local community. Again, hospital owner characteristics and educational function of each hospital were also important. With these factors controlled, it was found that monopsony power of each hospital was negative associated with the number of nurses per bed, as expected. 1% increase in monopsony power of each hospital(again measured by Herfindah-Hirschman Index) reduced the number of nurses per 100 bed as much as $0.46{\sim}0.67$. In conclusion. structural factors of nurse labor market influence the instability of nurse labor supply in Korea. Further consideration for these market structural characteristics needed for policy making related to nurse resource allocation.

• Human Ecology Research
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• 제53권5호
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• pp.519-530
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• 2015

This study examines the effects of coping resources on life satisfaction of middle and older caregivers looking after family members with activities of daily living disabilities. Personal resources and socio-relational resources were included as predictors after controlling for demographic characteristics. We studied 154 middle and 132 older adults drawn from the Korean Longitudinal Study of Ageing (KLoSA). The multiple regression results of this study were as follows. First, subjective health and family satisfaction had significant effects on middle-aged caregivers' life satisfaction. Specifically higher levels of subjective health and better relationships with their family predicted higher levels of life satisfaction. Second, cognitive function, household income, and family satisfaction had significant effects on middle-aged caregivers' life satisfaction. Higher household incomes, higher levels of cognitive function, and better relationships with family predicted higher levels of life satisfaction. For both middle and older adults, the effect size of family satisfaction was the largest out of all coping resources. The results revealed discrepancies regarding the importance of coping resources between middle and older caregivers, implying that developing interventions for middle and older caregivers (in accordance with their need for coping resources) is necessary. The results also indicated that having good relationships with one's family was the most important factor for both middle aged and older caregivers' life satisfaction. The results suggest that policies or services focused on endorsing healthy family relationships should be developed to improve the life satisfaction of caregivers.

• 한국디지털건축인테리어학회논문집
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• 제12권4호
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• pp.49-57
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• 2012

With regard to the culture in cities this study aims to essential understanding and systematic approach to the culture. The "2011 Seoul Survey"report has been used to find out causality among the related variables. In the first place 'satisfaction of cultural condition' was operationally selected as a dependent variable for regression. For the purpose of controlling confounding factors for ceteris paribus effect correlation analysis was done between the dependent variable and all other variables respectively, which resulted in two groups of variables: group (1) - 6 variables of very significant correlations(p-value<0.01) and (2) - the other 6 variables of significant correlations(p-value<0.05). Then hierarchical regression was adopted to these 2 groups to analyse $R^2$ increment, statistical significance of independent variables, and multicollinearity(VIF; variance inflation factor). At last a regression model specified by group (1) as independent variables(they are 'social trust', 'satisfaction of walking condition', 'happiness index', 'preparation against old age', 'satisfaction of traffic condition' and 'hours for internet') shows that only 'social trust' variable has statistically significant and substantially strong effect on 'satisfaction of cultural condition.' This finding should be accepted on the following understanding; (1) urban culture has a collective attribute formed between people and society, (2) culture is somewhat telling and hearing stories and the confidence between tellers and hearers is essential in the mutual response and (3) stimulus is received by relationship in company with sense, emotion, thinking and action. In spite of restrictive external validity this finding can be used as a direction for promoting culture and a basis for related policy choice in cities.

• 디지털콘텐츠학회 논문지
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• 제10권1호
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• pp.129-145
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• 2009

웹 환경에서 안전한 정보의 분배와 공유가 중요해짐에 따라 유동적이고 효율적인 접근 제어 시스템에 대한 요구 또한 나타나게 되었다. 또한 eXtensible Markup Language (XML)이 인터넷 시대에 정보를 저장 및 교환하기 위한 de-factor 표준으로 인식됨에 따라, 최근 보안을 고려한 XML 모델의 확장에 대한 연구가 활발히 진행되고 있다. 그러나 이러한 최근의 연구들은 여전히 XML 문서에 사용되는 데이터들이 관계형 데이터베이스에 저장 및 관리 되고 있다는 사실을 간과하고 있다. 따라서 이러한 연구들은 이미 많이 제안되고 검증된 관계형 데이터베이스에 대한 보안 모델을 활용 할 수 없다. 이 논문에서는 기존의 연구들과는 다른 접근 방법을 기술한다. 이 논문은 객체 관점에서 관계형 데이터베이스에 대한 보안 모델을 지원하기 위한 XML 보안 모델에 대한 연구에 초점을 둔다. 이 논문에서 제안하는 접근 방법에서는 (1) 사용자는 주어진 XML 뷰 또는 스키마에 XML 질의를 한다. (2) XML 데이터에 대한 접근 제어 규칙은 관계형 데이터베이스에 저장된다. (3) XML 문서의 데이터는 관계형 데이터베이스에 저장된다. (4) 접근 제어 및 질의 싱행은 관계형 데이터베이스 내에서 수행된다. (5) XML 접근 제어는 XML 트리 레벨을 고려하여 수행된다.