• Journal of Educational Research in Mathematics
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• v.15 no.1
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• pp.75-105
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• 2005

This study explored a mathematical modeling flow and the effect of interactions among students and between a student and Excel on modeling in a small group modeling environment with Excel. This is a case study of three 8th graders' modeling activity using Excel during their extra lessons. The conclusions drawn from this study are as follows: First, small group modeling using Excel was formed by formulating 4∼10 modeling cycles in each task. Students mainly formed tables and graphs and refined and simplified these models. Second, students mainly formed tables, algebraic formulas and graphs and refined tables considering each variable in detail by obtaining new data with inserting rows. In tables, students mainly explored many expected cases by changing the values of the parameters. In Graphs, students mainly identified a solution or confirmed the solution founded in a table. Meanwhile, students sometimes constructed graphs without a purpose and explored the problem situations by graphs mainly as related with searching a solution, identifying solutions that are found in the tables. Thus, the teacher's intervention is needed to help students use diverse representations properly in problem situations and explore floatingly and interactively using multi-representations that are connected numerically, symbolically and graphically. Sometimes students also perform unnecessary activities in producing data by dragging, searching a solution by 'trial and error' and exploring 'what if' modeling. It is considered that these unnecessary activities were caused by over-reliance on the Excel environment. Thus, the teacher's intervention is needed to complement the Excel environment and the paper-and-pencil environment properly.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.62-62
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• 2003

과학위성 1호에는 위성의 임무를 수행하기 위하여 광학계, 구조부, 및 전자부 등 여러가지 부품들이 실장되는데, 그 중 전자부의 가장 중요한 부품 중의 하나인 인쇄회로기판(Printed Circuit Board, PCB)의 우주환경에서의 특성 대해서 논의하고자 한다. Solder Resistor(Solder Mask)의 화학성분이 위성체가 작동하는 우주환경에서 위성체 임무수행 시 발생할 수 있는 out-gassing으로 인해 위성체가 본연의 임무 실패라는 결과를 초래할 수 있다 NASA 및 ESA의 Out-gassing에 관한 규정과 TRW에 의한 KOMSAT에 사용된 재료의 진공상태의 Outgassing에 관한 내용에 의하면, 재료의 진공상태와 Out-gassing은 America Society for Testing and Materials에서 제시한 ASTM E959 기준에 따라 제작된다. 일반적으로 우주 환경에서 광학계나 전자부의 원활한 동작을 위해서는 인쇄 회로 기판의 총 질량손실(Total Mass Loss, TML)은 1.00%을 넘지 말아야 하며, 휘발성 응축 질량 (Collected Volatile Condensable Mass, CVCM)은 0.1% 미만이어야 한다. Total Mass Loss(TML) 방법은 대기중에서 측정한 질량과 진공 조건에서 변화되는 질량을 측정함으로써 진공조건에서의 탈기체 특성을 측정하는 방법이다. 본 연구에서는 Solder Resistor(Solder Mask)의 탈기체 측정을 위한 진공챔버의 측정방법 및 진공 형성 과정을 기술하고 실제 과학위성1호에 장착될 시료를 예로 들어 인쇄회로기판에 입힌 Solder Resistor(Solder Mask)가 우주환경인 진공상태에서 위성체 부품의 작동 시 발생할 수 있는 탈기체되는 정도를 질량의 변화분으로 측정하여 위성체가 우주 환경에서 본연의 임무를 안전하게 수행할 있는지를 검증하였다.부분이다.다.향을 해석하고 시뮬레이션 하였다.Device Controller)는 ECU로부터 명령어를 받아서 arm 및 safe 상태에 대한 텔리 메트리 데이터를 제공한다 그리고, SAR(Solar Array Regulator)는 ECU로부터 Bypass Relay 및 ARM Relay에 관한 명령어를 받아 수행되며 그에 따른 텔리 메트리 데이터를 제공한다. 마지막으로 EPS 소프트웨어를 검증하는 EPS Software Verification을 수행하였다 전력계 소프트웨어의 설계의 검증 부분은 현재 설계 제작된 전력계 .소프트웨어의 동작 특성 이 위성 의 전체 운용개념과 연계하여 전력계 소프트웨어가 전력계 및 위성체의 요구조건을 만족시키는지를 확인하는데 있다. 전력계 운용 소프트웨어는 배터리의 충ㆍ방전을 효율적으로 관리해 3년의 임무 기간동안 위성체에 전력을 공급할 수 있도록 설계되어 있다this hot-core has a mass of 10sR1 which i:s about an order of magnitude larger those obtained by previous studies.previous studies.업순서들의 상관관계를 고려하여 보다 개선된 해를 구하기 위한 연구가 요구된다. 또한, 준비작업비용을 발생시키는 작업장의 작업순서결정에 대해서도 연구를 행하여, 보완작업비용과 준비비용을 고려한 GMMAL 작업순서문제를 해결하기 위한 연구가 수행되어야 할 것이다.로 이루어 져야 할 것이다.태를 보다 효율적으로 증진시킬 수 있는 대안이 마련되어져야 한다고 사료된다.$\ulcorner$순응$\lrcorner$의 범위를 벗어나지 않는다. 그렇기 때문에도 $\ulcorner$순응$\lrcorner$과 $\ulcorner$표현$\lrcorner$의 성격과 형태를 외형상으로

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.1
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• pp.71-88
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• 2003

The DRASTIC system is widely used for assessing regional groundwater pollution susceptibility by using hydrogeological factors such as depth to water, net recharge, aquifer media, soil media, topography, vadose zone media, hydraulic conductivity. This study is providing Modified Drastic Model to which lineament density, land use, influence of groundwater drawdown caused by tunnel excavation are added as additional factors using geographic information system, and then to evaluate groundwater contamination potential of ${\bigcirc}{\bigcirc}$ area. For statistical analysis, vector coverage per each factor is converted to grid layer and after each correlation coefficient between factors, covariance, variance, eigenvalue and eigenvector by principal component analysis of 3 direction, are calculated, correlation between factors is analyzed. Also after correlation coefficients between general DRASTIC layer and rated lineament density layer, between general DRASTIC layer and rated land use layer, between general DRASTIC layer and rated tunnel excavation influence layer are calculated, final modified DRASTIC model is constructed by using them with each weighting. When modified DRASTIC model was compared with general DRASTIC model, contamination potential in modified DRASTIC model is fairly detailed and consequently, vulnerable area which has high contamination potential could be presented concretly.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.11
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• pp.1024-1029
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• 2010

Use of polymeric soil amendments is an emerging way to reduce soil erosion, and improve crop productivity and soil quality. Objective of this study was to evaluate the effects of anionic polyacrylamide (PAM) and synthetic biopolymer on soil erosion, crop growth and soil quality. The aqueous solutions of PAM and biopolymer at 40 kg/ha were applied to loamy soil plots (3 m width by 18 m long) having a 20% slope during radish (Raphanus sativus) cultivation. Results showed that PAM and biopolymer treatments increased aggregate stability up to 11% compared to the untreated control. Treatments of PAM and biopolymer also increased leaf length of radish but there was no significant difference in crop yield. Soil loss was decreased by up to 41% using the polymeric soil amendments; however, no difference in runoff was found, compared to the untreated control. Soil loss was logarithmically increased against an increase in rainfall intensity ($R^2=0.85$). Our findings suggest that proper use of polymeric soil amendments would be beneficial to maintain soil quality and reduce soil erosion in sloping uplands.

• Economic and Environmental Geology
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• v.42 no.4
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• pp.335-342
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• 2009

The effects of bacterial lysis on the rate of quartz dissolution were investigated under pH 7 condition using Bacillus subtilis cells which were either irradiated or non-irradiated with gamma ray. The amount of dissolved organic carbon (DOC) which resulted from bacterial lysis increased in slurries of quartz and bacteria mixture over experimental period. Lysis of non-irradiated bacteria led to the elevated concentration of dissolved silicon when compared with abiotic control. Concomitant increase in the amounts of DOC and dissolved silicon over time indicated that lixiviation of silicon from quartz was due to bacterial lysis. Higher amounts of DOC and dissolved silicon were present in the irradiated bacterial slurries than those of non-irradiated bacteria. The enhancement of quartz dissolution in the irradiated bacterial slurries was likely attributed to disruption of organic molecules in the bacterial cells by gamma ray and formation of effective ligands for quartz dissolution. The results suggest that the effects of bacterial lysis on mineral weathering rate should be considered for prediction of time for released radionuclides to migrate to surface biosphere in high level radioactive waste disposal site.

• Journal of the Korean GEO-environmental Society
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• v.16 no.5
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• pp.35-42
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• 2015

This is conducted to observe underground temperature and to analyze its change affected by climate condition and soil infiltration in the mountainous area, Yesan region, Chungcheong-namdo province. Additionally, underground temperature change is also simulated using air temperature and soil thermal properties with a numerical model. Soil temperature monitoring data acquired from each depth, 20 cm, 50 cm, and 100 cm, indicates that the data within 50 cm in depth shows peak-shaped big fluctuation directly affected by air temperature and it at 100 cm has open-shaped small fluctuation. Underground temperature variation, a difference between high and low values, during monitoring period is weakly proportional to hydraulic conductivity of the sediment and it is assumed that water plays a part in delivering air temperature in soil. The underground temperature estimated by a numerical model is very similar to the observed data with an average value of 0.99 cross-correlation coefficient. From the result of this study, the aquifer unsaturated hydraulic conductivity of the soil and the groundwater recharge is likely to be able to estimate with underground temperature profile calculated using a numerical model.

• Journal of Korea Water Resources Association
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• v.48 no.9
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• pp.769-779
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• 2015

The streamflow depletion due to groundwater pumping from deep aquifer near the Juksan stream has been simulated, in this study, by using the surface water and groundwater integrated model, SWAT-ODFLOW in order to analyze the relationship between the stream depletion and hydraulic properties of aquifer and streambed, and to spatially assess the streamflow depletion. The simulated results showed that the streamflow depletion rate divided by the pumping rate for each well location ranges from 10% to 90% with reflecting the various well-stream distance, transmissivity, storativity, and streambed hydraulic conductance. In particular, the streamflow depletion exceeds about 50% of pumping rate for conditions with transmissivity higher than $10m^2/day$ or storage coefficient lower than 0.1. The simulated results in the form of spatial maps indicated that the spatially averaged percent depletion of streamflow is about 53.6% for five years of pumping which is lower than that for shallow aquifer pumping by 12.9%. From the spatially distributed stream depletion, it was found that higher and more rapid stream depletion to pumping occurs near middle-downstream reach.

• Journal of the Korean Geographical Society
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• v.42 no.6
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• pp.940-954
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• 2007

This study was to analyze a total of 18,068 farm reservoirs in Korea with their basic measures, and estimate their average characteristics. These characteristics have also been compared with those of foreign countries. Histograms of seven measures(approval area, beneficial area, watershed area, effective storage, full water area, dam length, and dam height) of reservoirs are made to characterize their distributions and to apply the Pareto analysis with the power law to evaluate their inequalities. The histogram analysis shows that the measures of dam(channel cross-section) characteristics follow the log-normal distributions, on the other hand, those of the basin characteristics the exponential-type distributions. Pareto analysis was done for the five measures of having exponential distribution. The Pareto exponents estimated are 0.38 for the approval area, 0.42 for the beneficial area, -0.19 for the effective storage, 0.30 for the watershed area, and 0.22 for the full water area, so the inequality of the beneficial area is the highest and that of the effective storage is the lowest. Analysis of morphology index versus watershed area shows that most reservoirs are categorized into deep or normal ones. These characteristics are also found to be similar to those of foreign countries.

• Elastomers and Composites
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• v.38 no.3
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• pp.213-226
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• 2003

The cure and rheological behavior of diglycidyl ether of bisphenol F/nadic methyl anhydride resin system with the kinds of imidazole were studied using a differential scanning calorimeter (DSC) and a rotational rheometer. The isothermal traces were employed to analyze cure reaction. The DGEBF/ anhydride conversion profiles showed autocatalyzed reaction characterized by maximum conversion rate at $20{\sim}40 %$ of the reaction. The rate constants ($k_1,\;k_2$) showed temperature dependance, but reaction order did not. The reaction order (m+n) was calculated to be close to 3. There are two reaction mechanisms with the kinds oi catalyst. The gel time was determined by using G'-G" crossover method, and the activation energy was obtained from this results. From measurement of rheological properties it was found that the logarithmic 1:elation time of fused silica filled DBEBF epoxy compounds linearly increased with the content of filler and decreased with temperature. The highly filled epoxy compounds showed typical pseudoplastic behavior, and the viscosity of those decreased with increasing maximum packing ratio.

• Journal of the Korean earth science society
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• v.28 no.2
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• pp.169-178
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• 2007

In this research we diagnosed the actual status of the 7th National science elective curriculum and suggested a way to select and organize the content of the new science elective curriculum. The first science education reform was grounded in the structuralism where the structure of discipline was valued above everything else. On the other hand, the second science education reform suggested alternative interpretations of students' opportunity to learn, putting a brake on the structuralist thinking. According to the survey result, the majority of the science elective courses are in need for revision because the contents are overcrowded, too difficult in light of students' learning readiness, failed to draw students' interest in science, and are overlapped and repeated among the 10th grade science, high school science I and II. In particular, Earth Science II and physics II are the most unfavorable courses among students. Thus, we recommended a fundamental change be made in the new curriculum in addition to the optimization of the content. In this paper, we suggested 'topic-centered content organization' for the science elective course I, i.e., Physics I, Chemistry I, Biology I and Earth Science I that is designed for both science track and non-science track students. Since curriculum provides students with an 'opportunity to learn', a curriculum study should focus on what the 'opportunity to learn' is that students ought to be offered. Based on the result of this study, we recommended one way to select and organize the content of high school elective curriculum.