• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.3
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• pp.129-134
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• 2013

Sapphire wafers are used as an important substrate for the production of blue LED (light emitting diode) and the LED's performance largely depends on the quality of the sapphire single crystals. There are several crystal growth methods for sapphire crystals and Kyropoulos method is an efficient way to grow large diameter and high-quality sapphire single crystals with low dislocation density. During Kyropoulos growth, the convection of molten melt is largely influenced by the hot zone geometry such as crucible shape, heater and refractory arrangements. In this study, CFD (computational fluid dynamics) simulations were performed according to the bottom/side ratios (per unit of the crucible surface area) of heaters. And, based on the results of analysis, the molten alumina flows and remelting phenomena were analyzed.

• Journal of Forest and Environmental Science
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• v.34 no.2
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• pp.165-168
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• 2018

Mt. Bongeui is a neighborhood park of 66.4 ha as a major natural landscape resource located in the center of Chuncheon City. This study quantified the reduction of carbon, $SO_2$, $NO_2$, $O_3$, and $PM_{2.5}$, and the production of $O_2$ to explore the role for Mt. Bongeui to contribute to annual atmospheric purification. The main forest types and age classes of the study site included age-class III broadleaved forest at 35.8%, age-class VI coniferous forest at 17.2%, and age-class IV broadleaved forest at 15.7%. The annual atmospheric purification effect per unit area was as follows: 7.6 t carbon/ha/yr, 16.6 kg $SO_2/ha/yr$, 40.4 kg $NO_2/ha/yr$, 41.5 kg $O_3/ha/yr$, 53.7 kg $PM_{2.5}/ha/yr$, and 20.2 t $O_2/ha/yr$. The economic value of these effects was equivalent to about 12.9 million KRW/ha/yr. The study site annually offset carbon emissions of about 300 citizens, $SO_2$ emissions of 220 citizens, and $NO_2$ emissions of 92 citizens in Chuncheon. It also played an important role in annually producing 1.5% of the amount of $O_2$ necessary for the respiration of Chuncheon's total population. This study pioneers in comprehensively quantifying the atmospheric purification effect and could be useful in guiding the planning and management to improve the effect.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.416-424
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• 1997

Mass transfer mechanism and concentration profiles in the axial direction at each phase were analyzed and simulated by a theoretical modeling on a liquid-liquid static contactor using highly packed fiber bundle. The concentrations at the end of the fiber extractor calculated at several operational conditions were compared with experimental results. The fiber extractor could be completely predicted by a plug flow model without axial dispersion. A parameter used in the model equations, $k_a{\sigma}$ called the product of mass transfer coefficient and mass transfer area per unit length of the fiber extractor in the axial direction, which was determined by a curve-fitting, was confirmed to be a unique characteristic value of the fiber extractor, and was about 0.0327cm2/sec.

• Journal of Radiation Protection and Research
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• v.41 no.2
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• pp.173-178
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• 2016

Background: In situ gamma spectrometry has been used to measure environmental radiation, assumptions are usually made about the depth distribution of the radionuclides of interest in the soil. The main limitation of in situ gamma spectrometry lies in determining the depth distribution of radionuclides. The objective of this study is to develop a method for subsurface characterization by in situ measurement. Materials and Methods: The peak to valley method based on the ratio of counting rate between the photoelectric peak and Compton region was applied to identify the depth distribution. The peak to valley method could be applied to establish the relation between the spectrally derived coefficients (Q) with relaxation mass per unit area (${\beta}$) for various depth distribution in soil. The in situ measurement results were verified by MCNP simulation and calculated correlation equation. In order to compare the depth distributions and contamination levels in decommissioning KRR site, in situ measurement and sampling results were compared. Results and Discussion: The in situ measurement results and MCNP simulation results show a good correlation for laboratory measurement. The simulation relationship between Q and source burial for the source layers have exponential relationship for a variety depth distributions. We applied the peak to valley method to contaminated decommissioning KRR site to determine a depth distribution and initial activity without sampling. The observed results has a good correlation, relative error between in situ measurement with sampling result is around 7% for depth distribution and 4% for initial activity. Conclusion: In this study, the vertical activity distribution and initial activity of $^{137}Cs$ could be identifying directly through in situ measurement. Therefore, the peak to valley method demonstrated good potential for assessment of the residual radioactivity for site remediation in decommissioning and contaminated site.

• Journal of the Korea Institute of Building Construction
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• v.14 no.6
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• pp.537-543
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• 2014

As environmental matters such as Green House Effect rise, many construction industries are putting an effort on minimizing environmental impact in terms of building life cycle throughout the world. However, in South Korea, evaluating the eco-friendly building based on life cycle assessment has been facing an academic ostracism while the most studies are focusing on assessing the 6 environmental impact assessments of passive apartment based on life cycle assessment. The theoretical consideration of the life cycle assessment and environmental impact category were performed and the direction of the study was set up. Also, existing apartment and passive apartment, which had same structure and same type were chosen and building materials per unit area were compared to find out the difference environmental impact for building life cycle. As a result, passive apartment was rated as low level among the 6 environmental impacts. Also, effect of building material on passive apartment was more important than its operational stage.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.181-187
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• 1997

The layered BaTiO3 thin films with a high dielectric constant of polycrystalline BaTiO3 and a good in-sulating property of amorphous BaTiO3 were prepared. And their electrical properties were characterized with stacking methods. The BaTiO3 thin films were prepared by rf-magnetron sputtering technique using a ceramic target on Indium-doped Tin oxide coated glasses. A new stacking method resulted in higher dielec-tric constant, capacitance per unit area, and breakdown strength than those prepared by a conventional stacking method; the new method continuously decrease the substrate temperature after initial deposition of a polycrystalline BaTiO3 layer. The observed high dielectric constant could be explained only by a mul-tilayered amorphous/microcrystalline/polycrystalline structure, which was confirmed indirectly by AES depth profile.

• Journal of Ecology and Environment
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• v.35 no.3
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• pp.177-188
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• 2012

We analyzed crown development in Aucuba japonica Thunb. var. japonica resulting from the responses of phytoelements to habitat light conditions over a long period of time. Over the years, the degree of extension unit (EU) dimorphism and the degree of anisophylly were higher under shaded conditions than in brighter conditions. An overall temporally increasing pattern in the degree of EU dimorphism was found while no clear-cut trend was found in the case of anisophylly. EU length and number of leaves per EU co-varied in a spatio-temporal context. The number of terminal buds and their sizes acted as the key initiators of morphological differences of phytoelements which were further amplified following bud break. Leaf area density was displayed mostly in the apex peripheral layer of the crown and the apex layer received most of the incident light. There was a tradeoff between annual leaf production and mean leaf size. Depending on the heterogeneity of irradiance level within a crown, correlative growth inhibition caused higher EU mortality at brighter sites. Due to high mortality, shorter EUs had a mere role in the construction of structural framework of the crown except for the formation of some gaps. There was a strong convergence of EU dimorphism, anisophylly, EU extension growth and variations in leaf size towards formation of functional crown to reduce potential self-shading. Depending on the irradiance level, Aucuba japonica Thunb. var. japonica showed two different modes of crown expansion. At the brighter sites, individual crown expansion was progressive while at the darker sites, individual crown expanded in a diminishing manner and maintained a stable size. A plant's "growth diminishing phase" appeared earlier at shaded sites than brighter sites.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.2
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• pp.145-153
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• 1984

In the present work, a computer simulation is performed employing Hottel-Whillier-Bliss model for thermal performance of solar collectors. The major collector parameters examined in the computer simulation are: number of transparent glass covers(N), thermal emissivity of the absorbing plate surface (.epsilon.$_{P}$), absorptivity of absorber plate (.alpha.$_{p}$), flow rate per unit area of collector (G), $L_{b}$ / $k_{b}$ of insulation material, tilt angle of collector (S), and solar insolation(I). By varying numerical values of the major collector parameters around their typical values, the corresponding variations in thermal efficiency curves are examined. In addition, an experimental investigation has been carried out with a slightly modified KAIST collector test loop under a real sun condition in order to compare with the simulation results, examine the applicability of the mathematical model of the collector thermal performance, and study the effect of variation of flow rate (G) on thermal efficiency and the range of optimum flow rate.e.

• Journal of the Korean School Mathematics Society
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• v.10 no.1
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• pp.129-148
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• 2007

Recent reform movement in mathematics education has focused not only on the curriculum development but also on teachers' learning or professional development. Whereas various theoretical paradigms call for different programs of professional development for teachers, one of the common emphases is on the pedagogical content knowledge [PCK] which encompasses contents and methods to teach. Against this background, this study developed comprehensive instructional materials for the purpose of fostering PCK in mathematics for elementary school teachers with 17 essential learning themes such as fraction, plane geometry, and area. Each loaming theme was first summarized on the basis of literature reviews and surveys in terms of knowledge in mathematics contents, knowledge in teaching methods, and knowledge in students' mathematical understanding and learning. Each theme was then analyzed in detail on how it was represented in the national curriculum and its concomitant textbooks along with workbooks. Finally, this report included a reconstruction of one unit in textbooks per each learning theme, followed by teaching notes and suggestions from classroom implementation. This was intended for teachers to apply what they might loam from this material to their actual mathematics instruction. Given the page limit, this paper dealt only with the learning theme of ratio.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.10
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• pp.162-170
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• 2013

In recent years, the interests and needs of the Pedestrian Protection System (PPS), which is mounted on the vehicle for the purpose of traffic safety improvement is increasing. In this paper, we propose a pedestrian candidate window extraction and unit cell histogram based HOG descriptor calculation methods. At pedestrian detection candidate windows extraction stage, the bright ratio of pedestrian and its circumference region, vertical edge projection, edge factor, and PCA reconstruction image are used. Dalal's HOG requires pixel based histogram calculation by Gaussian weights and trilinear interpolation on overlapping blocks, But our method performs Gaussian down-weight and computes histogram on a per-cell basis, and then the histogram is combined with the adjacent cell, so our method can be calculated faster than Dalal's method. Our PCA reconstruction error based pedestrian detection candidate window extraction method efficiently classifies background based on the difference between pedestrian's head and shoulder area. The proposed method improves detection speed compared to the conventional HOG just using image without any prior information from camera calibration or depth map obtained from stereo cameras.