• Korean Chemical Engineering Research
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• v.58 no.4
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• pp.642-650
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• 2020

In general, the circulation path of the fluidized particles in a CFB (Circulating Fluidized Bed) boiler is such that the particles entrained from a combustor are collected by a cyclone and recirculated to the combustor via a sealpot which is one of non-mechanical valves. However, when a fluidized bed heat exchanger (FBHE) is installed to additionally absorb heat from the fluidized particles, some particles in the sealpot pass through the FBHE and then flow into the combustor. At this time, in the FBHE operated in the bubbling fluidization regime, if the heat flow is not evenly distributed by poor mixing of the hot particles (800~950 ℃) flowing in from the sealpot, the heat exchanger tubes would be locally heated and then damaged, and the agglomeration of particles could also occur by formation of hot spot. This may affect the stable operation of the circulating fluidized bed. In this study, the unevenness of heat flow arising from structural problems of the FBHE of the domestic D-CFB boiler was found through the operating data analysis and the CPFD (Computational Particle Fluid Dynamics) simulation using Barracuda VR. Actually, the temperature of the heat exchanger tubes in the FBHE showed the closest correlation with the change in particle temperature of the sealpot. It was also found that the non-uniformity of the heat flow was caused by channeling of hot particles flowing in from the sealpot. However, it was difficult to eliminate the non-uniformity even though the fluidizing velocity of the FBHE was increased enough to fluidize hot particles vigorously. When the premixing zone for hot particles flowing in from the sealpot is installed and when the structure is changed through the symmetrization of the FBHE discharge line for particles reflowing into the combustor, the particle mixing and the uniformity of heat flow were found to be increased considerably. Therefore, it could be suggested that the structural modification of the FBHE, related to premixing and symmetric flow of hot particles, is an alternative to reduce the non-uniformity of the heat flow and to minimize the poor particle mixing.

• Korean Journal of Ecology and Environment
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• v.46 no.2
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• pp.145-153
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• 2013

It is a global trend that the water management policy is shifting from a water quality-oriented assessment to the aquatic ecosystem-based assessment. The majority of aquatic ecosystem assessment systems were developed solely based on physicochemical factors (e.g., water quality and bed structure) and a limited number of organisms (e.g., plankton and benthic organisms). Only a few systems use plants for a health assessment, although plants are sensitive indicators reflecting long-term disturbances and alterations in water regimes. The development of an assessment system is underway to evaluate and manage lakes as ecosystem units in the Korean Ministry of Environment. We reviewed the existing multivariate health assessment methods of other leading countries, and discussed their applicability to Korean lakes. The application of multivariate assessment methods is costly and time consuming, in addition to the correlation problem among variables. However, a single variable is not available at this moment, and the multivariate method is an appropriate system due to its multidimensional evaluation and cumulative data generation. We, therefore, discussed multivariate assessment methods in three steps: selecting metrics, scoring metrics and assessing indices. In the step of selecting metrics, the best available metrics are species-related variables, such as composition and abundance, as well as richness and diversity. Indicator species, such as sensitive species, are the most frequently used in other countries, but their system of classification in Korea is not yet complete. In terms of scoring metrics, the lack of reference lakes with little anthropogenic impact make this step difficult, and therefore, the use of relative scores among the investigated lakes is a suitable alternative. Overall, in spite of several limitations, the development of a plant-based multivariate assessment method in Korea is possible using mostly field research data. Later, it could be improved based on qualitative metrics on plant species, and with the emergence of further survey data.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.6
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• pp.735-744
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• 2007

The purpose of this study was to investigate the sweets preference, food frequency, dietary habits, and nutrition knowledge of middle school students who like sweets. A survey instrument consisted of a self-administered questionnaire, a food frequency questionnaire, and anthropometric measurements. Three hundreds thirty five students aged 13 to 15 years old were divided into two groups, Sweets Liking Group (SLG) and a control group based on the subjects' scores for dietary habits, sweets preference, and food frequency. For dietary habits, the score for meal regularity was significantly lower in the SLG group compared to the control (p<0.001). In addition, the SLG group was more likely to skip breakfast (p<0.001), eat inadequate amount of meals (p<0.001), and consume yellow-green vegetables less frequently (p<0.001) than the control. The subjects' nutrition knowledge was assessed using 20 questions representing five categories, including functions of nutrients, nutrition and health, food pyramid and food groups, healthful snacking and the right dietary attitude. The total scores for nutrition knowledge indicated that the SLG had a poorer nutrition knowledge for all five categories than the control (boys p<0.05, girls p<0.01). For food frequency, the SLG consumed more sweets but less grains, cereals, fishes, beans, vegetables, and milk and milk products than the control (p<0.001). Strong positive correlations appeared between sweets preference, sweets frequency, and sweets-related dietary habits; and all were negatively correlated to nutrition knowledge. Sweets frequency was negatively related to meal regularity, breakfast consumption, meal adequacy, and balanced meals. The findings suggest that nutrition education is necessary to improve the dietary pattern, especially sweets consumption, of Korean young adolescents.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.492-501
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• 2007

Coastal disasters have become one of the most important issues in every coastal country. In Korea, coastal disasters such as storm surge, sea level rise and extreme weather have placed many coastal regions in danger of being exposed or damaged during subsequent storms and gradual shoreline retreat. A storm surge is an onshore gush of water associated with a tow pressure weather system, typically in typhoon season. However, it is very difficult to predict storm surge height and inundation due to the irregularity of the course and intensity of a typhoon. To provide a new scheme of typhoon damage prediction model, the scenario which changes the central pressure, the maximum wind radius, the track and the proceeding speed by corresponding previous typhoon database, was composed. The virtual typhoon scenario database was constructed with individual scenario simulation and evaluation, in which it extracted the result from the scenario database of information of the hereafter typhoon and information due to climate change. This virtual typhoon scenario database will apply damage prediction information about a typhoon. This study performed construction and analysis of the simulation system with the storm surge/coastal inundation model at Masan coastal areas, and applied method for predicting using the scenario of the storm surge.

• Korean Security Journal
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• no.20
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• pp.339-363
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• 2009

The 9.11 demonstrated that terrorist attack could be more serious problem than the war in our modern life. No countries in the world have evaded being a target for terrorists today. As well as South Korea, the whole world must share attentions and responsibilities for fighting against the terrorism. Since the international terrorist groups have expanded their targets from Western countries to Koreans, civilian hostages are no longer other's affair; it became a serious threat to public. Increased Korean investment, trade, missionary, and travel overseas also expanded activity regions worldwide. It also result increased terrorist threats and possible abduction. The number of kidnapping crisis has increased since the terrorists use it as an effective method of sending a message. Piracy refers to a broad range of violent acts at sea, and has traditionally been regarded as common enemies. Piracy constitutes a great threat to the security of navigation as well as to the safety of vessels and crews. Lessons from hostage issues such as Korean hostage crisis in Somalia and Afghanistan show that it can cause criticism on moral issues if armed rescue missions fail or hostages are killed, so the governments and related corporations try to solve it by paying ransom. Terrorists and use these advantages in order to put a huge pressure on the governments. In this study we will look at essential characteristics and types of hostage abductions and recognition of national safety, lessons and solutions to previous Korean hostage cases in overseas. At the same time, it provides a guidelines of the direction in the fighting against terrorist groups and Piracy.

• Journal of Korean Home Economics Education Association
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• v.16 no.1
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• pp.63-77
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• 2004

The purpose of this study was to construct an issue-centered discussion instructional model for Home Economics and to determine its effect on middle school students' critical thinking. The research questions were posed as below. 1) The object and content of home economics in the 7th national middle school curricula are analyzed to sort out possible issues. 2) An issue-centered discussion instructional model is constructed to be applicable to middle school home economics class. and a lesson plan is prepared. 3) The effect of the issue-centered discussion instructional model developed in this study on student critical thinking faculty is examined. The findings of this study were as follows : First. seven criteria were selected to determine what types of issues were applicable to home economics lesson. Based on the selected criteria. 41 themes of issues were extracted from the 7th middle school textbooks. and their content validity was verified. Second, an issue-centered discussion instructional model was designed to deal with four themes in eight sessions in the procedure of problem raising, confirming, term defining. tentative alternative selecting, data gathering. discussing/critical approaching. and selecting/concluding. Third, two different third-year classes of K middle school in the city of Busan that consisted of 75 students were respectively selected as an experimental group and a control group, and the experiment was conducted in eight sessions for five weeks to see whether the teaching plan brought any changes to the critical mind of the students. The experimental group exposed to the issue-centered discussion lesson made a significant progress in critical thinking faculty(P＜.05). In particular. that instruction gave a favorable impact on demonstration evaluating(P＜.05). one of the critical thinking subfactors. When the students were asked to assess the issue-centered discussion lesson. most of them viewed it favorably. In the future, more research efforts should be dedicated to enhancing the practical applicability of issue-centered discussion instruction in home economics education. developing good evaluation tools about critical thinking faculty and finding out how discussion instruction could be conducted more efficiently.

• Journal of the Korean Chemical Society
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• v.62 no.4
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• pp.299-313
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• 2018

Inquiry-centered education is important in science education, but in the actual education field, scientific research is being done in a uniform manner due to realistic difficulties. In this study, we use RS (Reverse Science) as a secondary chemistry class to provide opportunities for students to engage in inquiry learning and scientific thinking through process-oriented activities. In this study, we developed and applied it to explore the effects on the scientific inquiry abilities of middle school students and checked the students' perception of it. For the application of the program, 128 students were selected from 6 classes of the 2nd grade in D district middle school, 64 from the experimental group and 64 from the comparative group. The experimental group taught RSP-based the chemistry inquiry programs and the comparative group taught instructor-led classes and verification experiments on the same topic over the seventh hour with three themes. In addition, we analyzed the results of the pre- and post-test by using the science inquiry ability test, and discussed the effects of the program based on the students' perceptions through class observation, student activity area, questionnaire and interview. As a result, the class using the program showed statistically significant changes in the science inquiry ability of secondary school students. Specifically, the experimental group was found to be significant in its prediction among the subcomponents of basic exploration ability compared to the comparative group. The differences have also been shown to be significant in terms of data translation, hypothesis setup and variable control, which are subcomponents of integrated exploration capabilities (p <. 05). In addition, students became interested in the process of creating the theory of science, and were highly interested in collaborating with their friends. It also provided students with opportunities to experience scientific thinking through process-oriented inquiry. Finally, based on the positive impact of the RSP-based chemistry inquiry program on students, we were able to identify the potential use of the program.

• Journal of the Korean earth science society
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• v.42 no.6
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• pp.770-788
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• 2021

This study aimed to determine whether middle school students could understand global warming and the greenhouse effect, and explain them in terms of global radiative equilibrium. From July 13 to July 24 in 2021, 118 students in the third grade of middle school, who completed a class module on 'atmosphere and weather', participated in an online assessment consisting of multiple-choice and written answers on radiative equilibrium, the greenhouse effect, and global warming; 97 complete responses were obtained. After analysis, it was found that over half the students (61.9%) correctly described the meaning of radiative equilibrium; however, their explanations frequently contained prior knowledge or specific examples outside of the presented data. The majority of the students (92.8%) knew that the greenhouse effect occurs within Earth's atmosphere, but many (32.0%) thought of the greenhouse effect as a state in which the radiative equilibrium is broken. Less than half the students (47.4%) answered correctly that radiative equilibrium occurs on both Earth and the Moon. Most of the students (69.1%) understood that atmospheric re-radiation is the cause of the greenhouse effect, but few (39.2%) answered correctly that the amount of surface radiation emitted is greater than the amount of solar radiation absorbed by the Earth's surface. In addition, about half the students (49.5%) had a good understanding of the relationship between the increase in greenhouse gases and the absorption of atmospheric gases, and the resulting reradiation to the surface. However, when asked about greenhouse gases increases, their thoughts on surface emissions were very diverse; 14.4% said they increased, 9.3% said there was no change, 7.2% said they decreased, and 18.6% gave no response. Radiation equilibrium, the greenhouse effect, and global warming are a large semantic network connected by the balance and interaction of the Earth system. This can thus serve as a conceptual system for students to understand, apply, and interpret climate change caused by global warming. Therefore, with the current climate change crisis facing mankind, sophisticated program development and classroom experiences should be provided to encourage students to think scientifically and establish scientific concepts based on accurate understanding, with follow-up studies conducted to observe the effects.