• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.1
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• pp.116-123
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• 2003

In this paper, interleaved boost converter is applied as a pre-regulator in switched mode power supply. The pre-regulator plays a role to improve power factor. Interleaved Boost Power Factor Corrector(IBPFC) can reduce input current ripple as a single voltage control loop only without inner current loop, because input current is divided each 50% by two switching devices. Each converter cell is also operated in discontinuous current mode and inductor current of each converter is discontinuous. Total input current which is composed by each converter cell is continuous current. Thus, IBPFC is able to improve input current ripple. IBPFC operating in discontinuous current mode can be classified as six modes from switching state and be carried out state space averaging small signal modeling. A control transfer function is obtained according to the modeling. Single voltage control loop is also constructed by the control transfer function. From experimental result, improvement of power factor and input current ripple are verified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.567-575
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• 2011

The development of space launch vehicle is an important step to advance to developed countries in the space area. It is also so risky due to necessity of huge costs and longer development period. The accuracy of cost estimation is important to develop a space launch vehicle successfully and efficiently. It is also necessary to estimate production and operation cost in order to develop commercial space launch vehicle possessing competitiveness. In this paper, Korean factors to be able to reflect the current state of workforce, average working hours and technology readiness level in Korea were analyzed to estimate production and operation cost of space launch vehicles that are developed in Korea. Korean factors have been applied to production and operation cost estimation of KSLV-II based on TRANSCOST. We evaluated the competitiveness level of KSLV-II as the commercial launch vehicle in the commercial launch services market by comparing with cost per flight of foreign launch vehicles.

• The Korean Journal of Food And Nutrition
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• v.19 no.4
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• pp.435-447
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• 2006

This study was carried out to investigate foodservice management of child care centers in Ansan and to suggest the basic data for foodservice management improvement. A questionnaire survey of 48 child care centers in Ansan was undertaken. Child care centers were categorized large (children eve. 100) and small(children less than 100) by size and public and private by type. Survey questionnaires consisted of general background, employee, food inspection and storage, kitchen, cooking facilities, food distribution and hygiene utensils. The results of this study are summarized as follows: because 46.9% to 56.3% of the centers took a dietitian in employment, foodservices in most of centers were not managed by professionals. The average of employee were 0.77 persons in smalll centers and 1.65 persons in large centers. The average space of kitchen were 3.86 pyung in smalll center, 6.06 pyung (1 pyung=$3.3058m^2$) in large centers. According to the data analyzed from Food inspection and storage, kitchen, cooking facilities, food distribution and hygiene utensils, the results indicate that the foodservice management of child care centers were in a relatively poor state. The director in child care centers should recognize the importance of the sanitation management and pay more attention to food service facilities. To improve foodservice performance at child care centers, it is required fur the Ministry of Gender Equality and Family to develop both the kitchen facility model based on the general sanitation standards and guidelines for child care centers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.1
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• pp.64-88
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• 2024

Security and reliability are the utmost importance facts in intelligent networked vehicles. Stochastic Petri Net and Z (SPZN) as an excellent formal verification tool for modeling concurrent systems, can effectively handles concurrent operations within a system, establishes relationships among components, and conducts verification and reasoning to ensure the system's safety and reliability in practical applications. However, the application of a system with numerous nodes to Petri Net often leads to the issue of state explosion. To tackle these challenges, a refinement and abstraction method based on SPZN is proposed in this paper. This approach can not only refine and abstract the Stochastic Petri Net but also establish a corresponding relationship with the Z language. In determining the implementation rate of transitions in Stochastic Petri Net, we employ the interval average and weighted average method, which significantly reduces the time and space complexity compared to alternative techniques and is suitable for expert systems at various levels. This reduction facilitates subsequent comprehensive system analysis and module analysis. Furthermore, by analyzing the properties of Markov Chain isomorphism in the case study, recommendations for minimizing system risks in the application of intelligent parking within the intelligent networked vehicle system can be put forward.

• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1485-1496
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• 2002

In order to investigate the fire-induced smoke movement in a three-dimensional room with an open door, numerical and experimental study was performed. The center, wall, and corner fire plumes for various sized fires were studied experimentally in a rectangular pool fire using methanol as a fuel. The numerical results from a self-developed SMEP (Smoke Movement Estimating Program) field model were compared with experimental results obtained in this and from literature. Comparisons of SMEP and experimental results have shown reasonable agreement. As the fire strength became larger for the center fires, the air mass flow rate in the door, average hot layer temperature, flame angle and mean flame height were observed to increase but the doorway-neutral-planeheight and the steady-state time were observed to decrease. Also as the wall effect became larger in room fires, the hot layer temperature, mean flame height, doorway-neutral-planeheight and steady-state time were observed to increase. In the egress point of view considering the smoke filling time and the early spread of plume in the room space, the results of the center fire appeared to be more dangerous as compared with the wall and the corner fire. Thus it is necessary to consider the wall effect as an important factor in designing efficient fire protection systems.

• Geomechanics and Engineering
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• v.30 no.1
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• pp.27-44
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• 2022

Gravelly soil is a kind of special geotechnical material, which is widely used in the subgrade engineering of railway, highway and airport. Its mechanical properties are very complex, and will greatly influence the stability of subgrade engineering. To investigate the mechanical properties and failure mechanism of gravelly soils, this paper introduced and verified a new discrete element method (DEM) of gravelly soils in large scale direct shear test, which considers the actual shape and broken characteristics of gravels. Then, the stress and strain characteristics, particle interaction, particle contact force, crack development and energy conversion in gravelly soils during the shear process were analyzed using this method. Moreover, the effects of gravel content (GC) on the mechanical properties and failure characteristics were discussed. The results reveal that as GC increases, the shear stress becomes more fluctuating, the peak shear stress increases, the volumetric strain tends to dilate, the average particle contact force increases, the cumulative number of cracks increases, and the shear failure plane becomes coarser. Higher GC will change the friction angle with a trend of "stability", "increase", and "stability". Differently, it affects the cohesion with a law of "increase", "stability" and "increase".

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1698-1711
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• 2024

Heat pipe cooled reactors have gained attention as a potential solution for nuclear power generation in space and deep sea applications because of their simple design, scalability, safety and reliability. However, under complex operating conditions, a control strategy for variable load operation is necessary. This paper presents a two-dimensional transient characteristics analysis program for a heat pipe cooled reactor and proposes a variable load control strategy using the recuperator bypass (CSURB). The program was verified against previous studies, and steady-state and step-load operating conditions were calculated. For normal operating condition, the predicted temperature distribution with constant heat pipe temperature boundary conditions agrees well with the literature, with a maximum temperature difference of 0.4 K. With the implementation of the control strategy using the recuperator bypass (CSURB) proposed in this paper, it becomes feasible to achieve variable load operation and return the system to a steady state solely through the self-regulation of the reactor, without the need to operate the control drum. The average temperature difference of the fuel does not exceed 1 % at the four power levels of 70 %,80 %, 90 % and 100 % Full power. The output power of the turbine can match the load change process, and the temperature difference between the inlet and outlet of the turbine increases as the power decreases.

• Land and Housing Review
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• v.4 no.2
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• pp.153-165
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• 2013

Deficiency in access to housing is a major manifestation of poverty. In the city of Bangalore, the poor and the marginalized constitute nearly 30 percent of the 8.47 million population (2011 Census) and are living in the nearly 640 slums in addition to squatter settlements and pavements. The city sprawls over an area of 741 sq. kms (2007 estimates) and the poor have very little access to personal living space. According to the Integrated Housing and Slum Development Program guidelines, each household with four average members should have 25 sq. meters of living space. In the case of poor of Bangalore, the attainment of even this minimum is a far cry. In recognition of this acuteness with regard to the problem of housing, the government has introduced schemes like the Jawaharlal Nehru National Urban Renewal Mission and the Rajiv Awas Yojana. And these schemes have witnessed only a limited success. Whenever the problem of housing for the urban poor is considered, the state and location of slums get into focus. The people living in slums are a crucial and inevitable support to the city economy. Relocation of slum people is fraught with loss of productivity and strain on the transport system and on the incomes of the poor. Their needs like housing, schooling, health centers, creches, hospices etc. have to be provided for. Financial support to the poor with regard to their housing needs will have to be imaginatively provided by banks and related institutions.

• Journal of the Korean Solar Energy Society
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• v.30 no.2
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• pp.87-95
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• 2010

This study analyzed the performance of solar chimney system for natural ventilation in underground space. A mathematical model of the solar chimney was proposed in order to predict its performance under varying parameters and Korea climatic condition. Steady state heat transfer equations were set up using a energy balanced equations and solved using a inverse matrix method. Numerical simulation program to analyze system was developed by using MATLAB. As the results, the ventilation performance of the solar chimney was determined by the temperature difference of air channel and inlet, and the temperature difference was influenced by insolation, stack height and distance of air gab. Also the solar chimney system can provide $262.9m^3/h$ of annual average ventilation rate. Because seasonal differences of ventilation rate was calculated within 25%, the solar chimney system can be used for every season in Korea climatic condition. Through this study, performance of solar chimney system for natural ventilation was verified by numerical method. Consequently, the solar chimney system is proved to be effective device for natural ventilation utilizing at all times, and the additional studies should be made through the experimental method for imagineering and commercialization.

• Journal of Korean Society of Transportation
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• v.19 no.3
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• pp.61-73
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• 2001

The purpose of this study is to simulate the suitable space of parking lots for Mass traffic instigating facilities in Pusan. After the suitable scale of parking lots estimate using GPSS, one of the Queue Simulation, with the average arriving time and the average parking time at parking lots, the formula is simulated by the Regression model to relate a total floor area and the suitable number of parking lots. The improved criteria or present parking lots is needed to prevent the unnecessary vehicles and improve the efficiency of land use. The suitable scale of parking lots estimate just with the state of using the parking lots in this study. but it is necessary to consider land use, traffic condition, commercial area etc.