• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.3
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• pp.403-411
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• 2001

The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. The brands studied were Unifil(GC, Japan), Palfique(Tokuyama Japan). Definite$Degussa-H\ddot{u}ls$ AG, Germany). Revolution(Kerr, U.S.A.). Preweighed discs of each brand were exposed 0.1N NaOH solution at $60^{\circ}C$. After 14 days they were removed, neutralized with HCl, washed with water and dried. Resistance to degradation was evaluated on the basis of following parameters: (a) mass loss(%) - determined from pre-and post-exposed specimen weights; (b) Si loss(ppm) - obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation depth$({\mu}m)$ - measured microscopically (SEM) from polished circular sections of exposed specimens. The results were follows: 1. The mass loss of Unifil was 3.21%, it was the highest of materials. But, there was no significant difference among the materials. 2. The degree of degradation layer depth was $107.69\sim47.40{\mu}m$, the sequence of the degree pf degradation layer depth was in descending order by Unifil, Palfique, Revolution, Definite. There was significant difference among the materials except Palfique and Definite. 3. The Si loss of Paltique was 8940.0ppm, it was the highest. There was significant difference among the materials, except Revolution and Definite(p<0.05). 4. The correlation coefficient between mass loss and degradation depth was relatively high(r = 0.06, p<0.05). 5. There was no significant coefficient correlation between Si loss and mass loss, and/or the degree of degradation layer depth and Si loss. 6. When observed with SEM, destruction of bonding is observed between resin matrix and filler. Above results suggested that the hydrolytic degradation is considered as evaluation factor of composite resins.

• Journal of the korean academy of Pediatric Dentistry
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• v.27 no.2
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• pp.274-282
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• 2000

Stainless steel crowns are widely used for restoration for primary molars. The material used for the crowns is an alloy of $70\sim80%$ nickel and $5\sim15%$ chromium. Nickel has been known to cause allergic reaction, cancer and cell toxicity. Little is known about nickel with respect to the relationship between Ni-contained SS crown and graining of Ni-resistance in oral microorganisms. The purpose of this study is to examine whether use of Ni-contained SS crown leads to occurrence of Ni-resistant microorganism, especially enterococci. The gingival crevicular fluid of two different groups was taken. Experimental group included patients wearing SS crown, and control group comprised individuals without SS crown. The samples were plated in BHI agar, BHI agar supplemented with nickel chloride at the concentration of 3mM and bile esculin azide (BEA) agar. The cultured enterococci on BEA agar medium were tested their Ni-resistance in nickel-containing media increasing concentrations from 3mM to 50mM. The results were as follows: 1. In experimental group, a total of 507,350 strains were isolated on BHI agar, of which 53,864(10.62%) strains were found to be resistant to 3mM nickel. In control group, of 414,590 isolates on BHI agar, 37,523 isolates were resistant to 3mM nickel. 2. A total of 95 enterococci were isolated on BEA agar in experimental group, while 20 were isolated in control group. of the enterococci, 68 and 12 isolates were found to be nickel-resistant in experimental and control group, respectively. 3. Of 68 nickel-resistant isolates in experimental group, one survived 50mM nickel. In contrast, none of the isolates in control group was observed to grow at the concentrations over 30mM nickel.

• Journal of The Korean Association For Science Education
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• v.35 no.4
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• pp.629-648
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• 2015

This study is a case study examining how research-based 'authentic' science education program contextually facilitates students' learning on NOS as a process. We developed 'Becoming a Scientist' mentor-mentee program and applied it to six Korean 7th graders for 8 months. A mentor, who is also a researcher, provided scaffolding and coaching, and her mentees were to perform the whole process of science research, including selecting the research subject and questions, planning research design, doing experiments, collecting and analysing data, writing research paper, and experiencing poster presentation at an academic conference. The research questions are 1) What would the students experience at every step of their research process?, and 2) Which perceptions would they construct NOS as a process? Data include classroom observations, interview, mentor's journal, and students' learning products. The results show that the mentees have experienced their views of NOS as a process in various ways such as role of research question and purpose, validity of measured value, researcher's subjectivity in interpreting data, experience of making public and peer review, and significance of academic conference. This study has shown that students' actual experience in scientific research enhanced their views about NOS as process without explicit and reflective approaches. We defined 'authenticity' associated with not only with its similarity to what scientists do but to learner's identity as scientific researcher. Based on the situated learning theory, this study sheds light on the necessity of reconsideration about the meaning of authenticity and embodying authentic context in science education for better NOS learning.

• Journal of The Korean Association For Science Education
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• v.31 no.4
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• pp.513-527
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• 2011

There have been studies about conceptual ecology making a profound study of conceptual changes in learners' cognitive structure. Because learners' cognitive structure have been compared to ecology, it is natural to think that conception in learner's cognitive structure have a niche as species in ecology have niches. Therefore, it is necessary to study niche approach about conception that learners recognize in their cognitive structure. The purposes of this study were to identify relationships among conceptions that 5th grade elementary school students recognize about photosynthesis and to identify how these relationships among conceptions about photosynthesis change before and after a class of photosynthesis in curriculum in terms of an approach of ecological niche which are composed of 3 domains - diversity of conceptions, relevance and frequency rate of conceptions, and competition among conceptions. Open ended questionnaire was developed by 4 fields: photosynthetic place, photosynthetic products, photosynthetic materials needed and environment factors of photosynthesis. The subjects sampled in this study were 310 5th grade elementary students in 5 cites. Before and after classes in photosynthesis in science curriculum, students were asked to write down conceptions that they knew about the 4 fields of photosynthesis of questionnaire and to write down scales of relevance from 1 to 30 about how they think the conceptions are related to the field of photosynthesis. The results of this study showed the following: First, most students have had a variety of conceptions and commonly recognized 'light' and 'water' as concepts in photosynthesis. Second, students still recognized their preconceptions like 'soil' and 'root,' etc. that were far from scientific conceptions of photosynthesis although they took classes in photosynthesis. Third, students needed to take the various strategies of teachers because they did not recognized scientific conceptions appropriately about photosynthetic fields. Fourth, it appeared that photosynthetic conceptions recognized by students had status in terms of relevance and frequency rate of conceptions, and competition among conceptions, and that they looked like the niche of conceptions in their conceptual ecologies.

• Journal of Yeungnam Medical Science
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• v.8 no.2
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• pp.174-184
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• 1991

To determine the incidence rate of accidents and its associated factors, a prospective survey was carried out in a rural area of a total of 1,360 residents for 1 year from January 1 to December 31, 1988 in Shin-am Ri, Jungdong Myun, Sangju Kun, Kyungpook Province. Data for accidents were collected by the community health practitioner who is working at Primary Health Post in Shin-am Ri. A total number of accident cases was 85 among 1,360 persons during one year study period, and annual incidence rate was 62.5 per 1,000 persons. The highest incidence rate of accident was observed in the age group of 30-39 was 179.8. The incidence rate of accident in male was 86.5 which was about 2 times that in female. In male, the highest incidence rate was seen in 30-39 age group and in female, 60-69 age group. The highest incidence rate of accident was observed in spring(29.4%) and summer(29.4%), and the lowest in fall(17.7%). The highest incidence rate of accident was observed in Friday(24.5%) by day of week, and between 9 a.m. to 12 a.m. by time zone. The most frequent use of medical facilities was Primary Health Post(51.8%) and the next was clinic(38.8%). Mean duration of treatment was 9.8 days. The accident occured in the room and kitchen(23.5%), in the yard and barn(23.5%), on the road(22.4%). and in the rice field and dry field(20.0%). The causes of accident were motor vehicle accident(20.0%), piercing or cutting(20.0%), collision or fighting(12.9%), and poisoning(11.8%) in order of frequency. The most common type of injury was open wound which was 43.5%. The most common tool of accident was farm machine which was 23.5%. The most common injuried part of body was extremity(55.3%).

• Investigative Magnetic Resonance Imaging
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• v.17 no.1
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• pp.19-25
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• 2013

Purpose : Renal blood oxygen level-dependent (BOLD) MRI has been used in the evaluation of renal oxygenation. We tried to provide the normal $R2^*$ value of the human kidney with 3.0 T, and evaluated the differences in $R2^*$ values according to gender and location. Materials and Methods: Twenty-four healthy volunteers underwent BOLD MRI at 3.0 T. Multi gradient echo-echo planar imaging sequence with seventeen echoes was used. After generation of the $T2^*$ map, the $R2^*$ was calculated. The statistical differences in $R2^*$ values between the cortex and medulla, males and females, and the right and left kidney were analyzed. The regional differences of $R2^*$ within the both kidneys were evaluated respectively. Results: BOLD MRI was successful in all participants. No gross artifact interfered with $R2^*$ measurement. The mean $R2^*$ at 3.0 T was $17.1{\pm}2.60s^{-1}$ in the cortex and $27.7{\pm}4.83s^{-1}$ in the medulla (p < 0.001). The $R2^*$ value in the medulla was significantly higher in the male than female volunteers (p = 0.025). There were no statistical differences of $R2^*$ according to the side and location in the kidney (p = 0.197). Conclusion: Renal BOLD MRI can be efficiently performed with 3.0 T MRI. Renal medullary hypoxia is present in normal volunteers. Our results may be used as reference values in the evaluation of pathologic conditions using BOLD MRI.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.5
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• pp.591-610
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• 2020

Concrete with activated carbon and titanium dioxide (TiO₂) has been used to reduce the particulate matter (PM) in underground structures (e.g., tunnels) due to the high performance of nitrogen oxides (NOx) abatement. Damage (e.g. crack, spalling, or detachment) can be caused by the environmental and ageing effects on the surface of the particulate matter reduction concrete, installed on the tunnel lining. Therefore, it is important to evaluate the existence of spalling on the concrete surface for maintaining performance of NOx reduction. In this study, a basic research was performed for feasibility of spalling evaluation using electrical resistivity characteristics. Given the test results, the electrical resistivity was decreased as the ratios of activated carbon (0~15%) and TiO₂ (0~25%) were increased for specimens. Under a dry condition, electrical resistivity of cement specimens, mixed with activated carbon and TiO₂, was decreased up to 2.3 times, compared with the normal cement specimen. In addition, under saturation conditions (degree of saturation: 85~98%), electrical resistivity of cement specimens with activated carbon, was decreased up to 3.5 times, compared with the normal cement specimen. Regardless of the condition (dry or saturated), the difference of electrical resistivity values shows the range of 2.3~2.8 times between the mixing specimen (with activated carbon (15%) and TiO₂ (25%)) and the normal cement specimen. This study can help to provide basic knowledge for spalling evaluation using the electrical resistivity on the surface of the particulate matter reduction concrete in tunnels.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.5
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• pp.727-743
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• 1996

To know the floristic composition, vortical distribution and community structure of marine benthic algae inhabiting in the intertidal and subtidal zones of Yongil Bay, east coast of Korea, the study has performed using the quadrat method along a transect line from July, 1995 to June, 1996. In this area, a total of 144 species including 2 new red algae to Korea was found: 5 blue-green, 18 green, 20 brown and 101 red algae. The representative species throughout the year were Ulva pertusa, Gelidium amansii and Symphyocladia latiuscula. Dominant species were Sargassum thunbergii in spring, U. pertusa in summer and autumn. In winter, Chondrus ocellatus and Monostroma grevillei occurred dominantly. The standing crop exhibited mean value as $185.8g/m^2$ dry weight. Maximum value was recorded in spring $(267.3g/m^2)$ and minimum was observed in winter $(93.7g/m^2)$. Shannon's species diversity (H') and evenness (J') as maximum value were recorded in spring, whereas minimum values were shown in winter. Vertical distribution, rerognized by cluster analysis based on relative coverage of the species, could be divided into two or three algal groups except spring. In general, green algae (M. grevillei, Capsosiphon fulvescens, U. pefusa, Enteromorpha compressa) and brown algae (Sargassum fulvellum, S. thunbergii) were represented in the upper and middle zone and red algae (G. amansii, C. ocellatus, S. latiuscula, Crateloupia okamurae, Pachymeniopsis eilliptica) in the lower zone. The algal community varied according to season and environmental conditions. Particularly, seasonal variation of vortical distribution seemed to be affected primarily by water temperature. Also seasonal tidal level and tolerance of algal species to desiccation appeared to be associated with it in this area.

• Journal of the Korean Institute of Landscape Architecture
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• v.40 no.6
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• pp.23-34
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• 2012

This Study is about the "Comprehensive Landscape Improvement Plan for Gu-ryoung Seaside Village that was one of most exhibited projects for developing sea villages." The formulations of the plan were supervised by the Ministry of Land, Transport, and Maritime Affairs and were executed by the Goheung Country. Rather than proposing renovations for the landscape, this study maintains the existing order and attempts to examine the plan by scrutinizing the vernacular design language of the landscape. In the study, community members had the opportunity to express their opinions and ideas about the community through workshops composed of community participation programs, and participated in the decision-making process through consultation meetings. The conclusion of this study was relevant to the activities of the committee on landscape improvement. The Comprehensive Landscape Improvement Plan has three objectives: (1) resorting and modifying the natural landscape, (2) restructuring the roadways, and (3) modifying key spaces. In the end, the role of Gu-ryong Mountain as a background of the landscape was focused on tree planting drives that were undertaken, and accessibility to the sea front was improved. Second, in restructuring the roadways, rough roads were restored and unconnected roads were connected to ensure a network of roads along the sea front, inner roads in the village, roads at the Fringes Mountains, and stone roads on the mud flat. In addition, roads were named according to the character of the landscape and signs were installed. Finally, the existing key spaces, in which community members came together, were restored and new key spaces were created for the outdoor activities of the inhabitants and the diverse experience of visitors. A guideline was also created to regulate private areas such as roofs, walls, fences of residential buildings, and private container boxes and fishing gear along the sea front. The strength of this study is that it is seeking to determine the greatest potential of the landscape and set the plan by examining the lives of community members. Some problems were found during the development of this study. Further, there were problems in the community's understanding as elaborated below. First is the gap between community members' awareness and practice. Even though they were aware of the problems with the village landscape, they hesitated to implement improvements. Second, community members have misunderstandings about the landscape the improvement plan. The local government and the residents have understood this plan as a development project; for example, new building construction or the extension of roads. Third, residents are not aware that continuous attention and improvements are required for the upkeep of the landscape in the sea village. The plan to improve the landscape should promote a balance between making the area as a tourist attraction and maintaining the lives and cultural activities, because the sea village system incorporates settlements, economy, and culture.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.197-210
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• 2012

Hematite has been known to be the most stable form of various iron (oxyhydr)oxides in the surface environments. In this study, its properties as an adsorbent were examined and also adsorption of arsenic onto hematite was characterized as well. The specific surface area of hematite synthesized in our laboratory appeared to be $31.8g\;m^2/g$ and its point of zero salt effect, (PZSE) determined by potentiometric titration was observed 8.5. These features of hematite may contribute to high capacity of arsenic adsorption. From several adsorption experiments undertaken at the identical solution concentrations over pH 2~12, the adsorption of As(III) (arsenite) was greater than that of As(V) (arsenate). As of pH-dependent adsorption patterns, in addition, arsenite adsorption gradually increased until pH 9.2 and then sharply decreased with pH, whereas adsorption of arsenate was greatest at pH 2.0 and steadily decreased with the increasing pH from 2 to 12. The characteristics of these pH-dependent adsorption patterns might be caused by combined effects of the variation in the chemical speciation of arsenic and the surface charge of hematite. The experimental results on adsorption kinetics show that adsorption of both arsenic species onto hematite approached equilibrium within 20 h. Additionally, the pseudo-second-order model was evaluated to be the best fit for the adsorption kinetics of arsenic onto hematite, regardless of arsenic species, and the rate constant of As(V) adsorption was investigated to be larger than that of As(III).