• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.216-227
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• 2004

A new cavitating model by using bubble size distribution based on bubbles-mass has been proposed. Both liquid and vapor phases are treated with Eulerian framework as a mixture containing minute cavitating bubbles. In addition vapor phase consists of various sizes of vapor bubbles, which are distributed to classes based on their mass. The bubble number-density for each class was solved by considering the change of the bubble-mass due to phase change as well as generation of new bubbles due to heterogeneous nucleation. In this method, the bubble-mass is treated as an independent variable, and the other dependent variables are solved in spatial coordinates and bubble-mass coordinate. Firstly, we employed this method to calculate bubble nucleation and growth in stationary super-heated liquid nitrogen, and bubble collapse in stationary sub-cooled one. In the case of bubble growth in super-heated liquid, bubble number-density of the smallest class based on its mass is increased due to the nucleation. These new bubbles grow with time, and the bubbles shift to larger class. Therefore void fraction of each class is increased due to the growth in the whole class. On the other hand, in the case of bubble collapse in sub-cooled liquid, the existing bubbles are contracted, and then they shift to smaller class. It finally becomes extinct at the smallest one. Secondly, the present method is applied to a cavitating flow around NACA00l5 foil. Liquid nitrogen and liquid oxygen are employed as working fluids. Cavitation number, $\sigma$, is fixed at 0.15, inlet velocities are changed at 5, 10, 20 and 50m/s. Inlet temperatures are 90K in case of liquid nitrogen, and 90K and 1l0K in case of liquid oxygen. 110K of oxygen is corresponding to the 90K of nitrogen because of the same relative temperature to the critical one, $T_{r}$=$T/T_c^{+}$. Cavitating flow around the NACA0015 foils was properly analyzed by using bubble size distribution. Finally, the method is applied to a cavitating flow in an inducer of the LE-7A hydrogen turbo-pump. This inducer has 3 spiral foils. However, for simplicity, 2D calculation was carried out in an unrolled channel at 0.9R cross-section. The channel moves against the fluid at a peripheral velocity corresponding to the inducer revolutions. Total inlet pressure, $Pt_{in}$, is set at l00KPa, because cavitation is not generated at a design point, $Pt_{in}$=260KPa. The bubbles occur upstream of the foils and collapse between them. Cavitating flow in the inducer was successfully predicted by using the bubble size distribution.

• Journal of Environmental Health Sciences
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• v.44 no.1
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• pp.44-54
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• 2018

Objectives: To protect individuals working at the site as well as the surrounding general population from a chemical accident, several emergency exposure guidance levels have been used to set a level of concern for certain chemicals. However, a level of concern has not been established for many substances that are frequently used or produced in large quantities in Korean workplaces. In the present study, we investigated the guidance levels for protecting populations from chemical exposure and the estimation of level of concern using acute inhalation and oral toxicity data. Methods: The number of chemicals to which emergency exposure guidance levels (e.g., ERPG-2, AEGL-2, PAC-2, and IDLH) can be applied were determined among 822 hazardous chemicals according to the 'Technical Guidelines for the Selection of Accident Scenarios (revised December 2016)'. The ERPG and AEGL values were compared across all three tiers for the 31 substances that appeared on both lists. We examined the degree of difference between the emergency exposure guidance levels and the estimates of level of concern calculated from acute inhalation or acute oral toxicity data. Results: Among the 822 hazardous chemicals, emergency exposure guidance levels can be applied to 359 substances, suggesting that the estimates of level of concern should be calculated using acute toxicity data for 56.3% of the hazardous chemicals. When comparing the concordance rates of ERPG and AEGL for 31 substances, the difference between the two criteria was generally small. However, about 40% of the substances have values diverging by more than three-fold in at least one tier. Such discrepancies may cause interpretation and communication problems in risk management. The emergency exposure guidance levels were similar to the estimates of level of concern calculated using acute inhalation toxicity data, but the differences were significant when using acute oral toxicity data. These results indicate that the level of concern derived from acute oral toxicity data may be insufficient to protect the population in some cases. Conclusion: Our study suggests that the development of standardized guidance values for emergency chemical exposure in the Korean population should be encouraged. It is also necessary to analyze acute toxicity data and fill the information gaps for substances that are important in Korean workplace situations.

• 대한공업교육학회지
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• v.41 no.1
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• pp.88-107
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• 2016

Hatching and developing great human resource is getting important in these competitive business environments. It is important to define and utilize personalized competence model for individual firm before hatching and developing its HR. Competence is a unique set of behavior shown as a result of sum of knowledge, skill, value and other personal traits in his/her working environment and the systematic process finding and defining the competence is called competence modeling. The purpose of this study was to perform competence modeling for a small-medium size IT firm N especially for its salespeople and offer suggestions of the usage of the result. Competence model was developed by 'Covering general model' suggested by Dubois. To confirm the validity, survey and workshop was conducted and the model was finalized based on the results. As a result, total 14 core competencies were found and defined by the core salesperson of the firm N. Also the competencies were categorized into three based on the timing of the usage. Additionally, this study offers the ways to utilize the result as foundation for competence based HR system and HRD program for firm N.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1682-1694
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• 2007

There are a lot of factors working to facilitate the decline of Korea's traditional markets including large-scale discount stores, convenience stores, businesses of new types such as non-store retailing, and fiercer competitions among retail shops. The changes to the business environment are never favorable to them, either; the consumers have developed more diverse tastes and altered their purchasing styles; and the trading areas around traditional markets have withdrawn in size and power as new towns attract more businesses. In a word, every factor and situation seems to push traditional markets down the slope. Reacting to the problems, the Korean government enacted and enforced the "Special Law for the Promotion of Traditional Markets and Shopping Streets" to provide proper financial and management support. The shop owners of traditional markets formed merchants and prosperity associations and took various initiatives to increase the competitive edge of their traditional markets. All those efforts on the part of the government and the merchants, however, do not seem to be enough to revive traditional markets. This study set out to compare and analyze the management of shop owners of traditional markets based on the support projects by the government, to conduct an empirical research and analysis of their management conditions, and to suggest a better policy model by making improvements for the government's support system and making revisions to the current directions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.9
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• pp.744-750
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• 2013

In this paper, we proposed new type of an artificial magnetic conductor(AMC) structure, which has a high impedance surface for realizing the meta-material characteristics. The designed AMC structure set a goal of 3.2GHz, and the reflector, which consists of periodically arrayed AMCs is fabricated and measured. The high impedance improves the reflection coefficient, decreases the system size and interference, and increases the antenna performance. The structure has embodied the high impedance by the thickness and relative permitivity of the dielectric substrate and the design configuration without the metallic via hole which connects the AMC to the GND. The bandwidth is 150% broader than the similar AMC structures. Also, the distance between the antenna and the AMC reflector is decreased by ${\lambda}/10$ as working as the metal(PEC) reflectors. The antenna radiation characteristics are 3dB increased at 10mm away from reflector by measurement. The proposed reflector could be inserted in the portable mobile devices, and the antenna's performance has improved by the reflector. The specific absorption rate is dramatically decreased over 94% because the back radiation of the antenna is shielded.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.866-872
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• 2010

In this paper, we developed a digital soldering station based on PID controller, which supply stable power by controlling the current of heater of soldering iron. The proposed system designed PID controller to converge quickly to the set up temperature by user, and regain the lost of heat by external factors quickly. PID controller, designed by Ziegler-Nichols' tuning method, decides triac's trigger timing using setting temperature and present temperature to control the phase of AC 24V power that supply to the heater. Also, we give the function that shows present temperature and setting temperature of iron, and working time by graphic LCD. And during the rest time, we decided the power saving and extension of iron tip by dropping to the optimal temperature. Two experiments had implemented in $25^{\circ}C$ laboratory to confirm the performance of proposed method. The first experiment took 12sec, 13sec, 16sec, 18sec, reaching to $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ respectively which result showed shorten of rising time than previous method. In the loading experiment of $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ steady state showed temperature drop of $3.8^{\circ}C$, $4.1^{\circ}C$, $4.5^{\circ}C$ which result showed the low temperature deviation than previous method.

• KIEAE Journal
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• v.17 no.5
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• pp.51-59
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• 2017

Purpose: This study aims to set up the classification system for providing infill information and draw detailed infill information required by suppliers, thereby promoting the revitalization of long-life housing and utilizing such information as preliminary data for establishing web system, on which infill information required by users in the long-life housing design process are available. Method: For the method of study, the infill information classification system and detailed information were drawn through the analysis of existing building material information systems; and the survey targeting working-level personnel was carried out in order to verify the drawn information system. The results of this study can be summarized as follows. First, the hierarchical classification system (scheme) was selected by quoting the classification system by material type as infill type, after analyzing existing DB information systems and drawing the hierarchical classification system for infill. Second, the comparative analysis between infill was available to users for the detailed infill information of long-life housing, and the essential information and general information were selected for differentiating information. Results: First, the hierarchical classification system (scheme) was selected by quoting the classification system by material type as infill type, after analyzing existing DB information systems and drawing the hierarchical classification system for infill. Second, the comparative analysis between infill was available to users for the detailed infill information of long-life housing, and the essential information and general information were selected for differentiating information. Third, only approximately 30% of the survey respondents recognized the infill of long-life housing, but they did not recognize its difference from existing building materials. Fourth, through the analysis of paths to obtain infill information of long-life housing, it was confirmed that infill information was obtained mostly through books and research papers regarding long-life housing, followed by the existing information systems. The significance of the study lies in that it is differentiated from the previous information system as the information system specialized in the infill of long-life housing was established, and can be used as a measure to revitalize long-life housing market.

• The Journal of the Korea Contents Association
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• v.9 no.6
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• pp.289-299
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• 2009

This study set out to analyze the perceptions of investigative police officers and division police officers regarding Police Investigation Specialization, which had been in effect for four years, identify the problems, and search for alternative policies. The results led to the following alternative policies; first, the communication among the members should be facilitated by trading the jobs between investigative policemen and division members in certain percentage regularly, integrating job education and special work, and developing diverse support programs for detective activities to provide them with opportunities to experience and understand investigation. The second suggestion concerns the investigation members' morale. There should be a range of measures to boost their moral such as allocating separate budget and personnel to support the investigation department and the treatment of major criminal and civil cases, giving each investigation team an office and investigation room to improve their working environment, readjusting the promotion ratio of Police Investigation Specialization to introduce a promotion system proper for each investigation's characteristics. The third suggestion is to secure job efficiency. It's required to reinforce the current short-term specialized education program to bring up practical and professional investigators, open the certification exam of professional investigators to all members so that every policeman can have their abilities recognized and approved as long as they have the demanded capabilities, and create a system of shedding off the members idle at work by reflecting low performance records when evaluating the members to decide who to dismiss from Police Investigation Specialization. And finally, it's important to divide duties rationally. The rationality of duties division can be guaranteed by setting the guidelines for direct handling for the team leader to help him devote himself to his duties, defining objective criteria of measuring investigation workload, and creating devoted systems and teams for simple and small accidents so that experienced investigators can deal with high-profile cases.

• Resources Recycling
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• v.15 no.4 s.72
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• pp.36-43
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• 2006

There was some difficulty dewatering properties due to small porosity diameter of cake, when pigment sludge contained fine particle was formed by cake under the dewatering. It was difficult to dewater the sludge with fine particles with the conventional mechanical dewatering method. This study was to improve the dewatering rate as discharging the water from porosity of cake easily, supplying the low heat to the cake layer. Thermal dewatering equipment of piston type to keep up constant temperature on the cake was set up and relative experiment was conducted for sludge of 200 g with fine pigment particle. As test results. filtration of 176.8 g, cake weight of 19.4 g, cake thickness of 4.2 mm was measured, and it was analyzed that the water content of cake was 47 wt% and dewatering velocity, which moaned the residual d교 sloid amount per dewatering area, was $2.1DS\;m^{2}{\cdot}cycle$. This results showed that filtration increased, cake weight and thickness decreased and dewatering velocity increased against mechanical dewatering method. And water content of cake decreased about 30%, so the result which dewatering rate improved was drew generally. The reason is that the inner vapor pressure working at the cake porosity increased as applying the low heat to the cake layer, which lead to discharge the water from porosity easily. Therefore, this study was estimated by the useful technology for sludge reduction.

• Korean Journal of Social Welfare Studies
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• v.48 no.2
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• pp.203-231
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• 2017

The purpose of this study is to examine the impact of organizational climate on the resource linking skills of social workers working in community welfare centers as well as the mediating effects of reflective thinking in these relationships. To test the mediating effects, we set up a research model based on previous studies on the organizational climate, resource linkage skills, and reflective thinking of social workers. The subjects of this study were social workers in community welfare centers in the Busan metropolitan city. Data were collected using mail surveys, and data from 526 respondents were used for the final analysis. The main results are as follows. First, the organizational climate of community welfare centers has a statistically significant impact on social workers' resource linkage skills. In other words, the more the social workers recognize positively about the organizational climate, the more the utilization of resource linkage skills increases. Second, reflective thinking has a mediating effect in the relationship between the organizational climate and resource linkage skills of social workers in community welfare centers. Based on the study results, practical suggestions for improved resource linkage skills and reflective thinking of social workers in community welfare centers were suggested, and practical implications and future research were discussed.