• Journal of the Korean School Mathematics Society
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• v.23 no.4
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• pp.509-521
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• 2020

This study began with the discovery of the concept of frequency density in Singapore textbooks and in a set of subject contents of the UK's General Certificate of Secondary Education. To understand the mathematical meaning of frequency density, the mathematical connection of frequency density was considered in terms of mathematics internal connections and mathematics external connections. In addition, the teaching method of frequency density was introduced. In terms of mathematical internal connections, the connections among the probability density function, relative frequency density, and frequency density in high school statistics were examined. Regarding mathematical external connections, the connection with the density concept in middle school science was analyzed. Based on the mathematical connection, the study suggested the need to introduce the frequency density concept. For the teaching method of frequency density, the Singapore secondary mathematics textbook was introduced. The Singapore textbook introduces frequency density to correctly represent and accurately interpret data in histograms with unequal class intervals. Therefore, by introducing frequency density, Korea can consistently teach probability density function, relative frequency density, and frequency density, emphasizing the mathematical internal connections among them and considering the external connections with the science subject. Furthermore, as a teaching method of frequency density, we can consider the method provided in the Singapore textbook.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.163-163
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• 2011

평활입자동역학법(SPH, Smoothed Particle Hydrodynamics)은 붕괴파(도수, 댐붕괴류, 쇄파) 등과 같이 수면 변동이 큰 유체 역학 문제를 해결하기 위한 무격자법 중의 하나이다. SPH를 이용한 붕괴파의 모의에서는 압력, 점성, 밀도(압축성), 척력 등 다양한 계산 인자가 필요하다. 이들 인자가 SPH 모의 결과에 미치는 영향을 도수와 댐붕괴류에 대해서 검토하였다. 그 결과 압력과 관련하여, 상태 방정식 계수로 표현되는 유체의 음속은 입자들의 흩어짐 현상과 밀접한 관계를 가지는 것을 밝혀내었다. 평활 거리는 수치해의 안정성과 밀접한 관련이 있으며, 너무 작거나 크게 설정하는 경우 해의 정확도가 떨어지는 것으로 나타났다. 일반적으로 2차원 문제의 경우 20~23개 정도의 입자가 해의 내삽에 사용되는 것이 바람직하다.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1737-1740
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• 2006

본 연구에서는 1차원 수치모형을 이용하여 댐 여수로에서 발생하는 흐름을 해석하였다. 본 연구에서 사용한 1차원 수치모형은 매우 복잡한 지형에 적용이 가능하며, 상류가 사류가 동시에 발생하거나 도수가 발생하는 흐름도 해석할 수 있는 모형이다. 이 모형은 해석해를 가지는 도수의 경우에 적용하여 검증된 바 있으며, 자연하천의 보에서 발생하는 불연속 흐름에 대해서도 적용된 바 있다. 또한 매우 불규칙한 자연하천에서 발생하는 흐름도 효과적으로 모의할 수 있다. 본 연구에서는 댐 여수로 흐름 해석을 평가하기 위해 단순화된 하도에서 발생하는 불연속 흐름에 대해 이론적인 해와 비교하였다. 또한 댐 수리모형 결과에 수치모형을 적용하여 빈도별로 발생하는 흐름을 해석하였다. 해석결과 여수로에서 발생하는 매우 작은 수심을 정확하게 모의하였으며, 여수로 직하류부에서 발생하는 도수의 발생위치, 발생 전후의 수위도 잘 모의하는 것으로 나타났다. 또한 여수로 및 도수 전후에 발생하는 유속도 정확하게 모의하는 것으로 나타났다. 또한 본 연구에서는 1차원 수치모형을 여수로 뿐만아니라 댐 상류 하천, 저수부, 여수로 접근수로, 여수로, 도수, 하류하천등으로 구성되는 전 구간의 흐름을 동시에 모의하기 적용하였다. 적용 결과 댐 저수지 상류 하천과 저수지, 저수지와 접근수로, 접근 수로와 여수로, 여수로와 도수, 도수 발생 후와 하류하천 등에서 복잡하게 형성되는 흐름을 동시에 잘 모의하는 것으로 나타났다. 본 연구에서 사용한 1차원 수치모형을 이용하면 댐 여수로나 저수지, 연계되어 있는 상하류 하천에서의 흐름을 동시에 해석할 수 있기 때문에 향후 수리모형실험과 연계하여 댐 설계에 효율적으로 사용될 수 있을 것으로 전망된다.지는 것으로 평가되었다. 그러나 본 연구결과를 통하여 투수성 포장과 지하수에 관련된 매개변수의 집적과 분석결과는 현장기술 적용 시 매개변수의 유용한 선택과 도시유역의 물 순환 건전화 대안기술 적용에 효과적인 방법론을 제시할 수 있을 것으로 사료된다.첨두홍수량을 저류하기 위해서 상대적으로 넓은 저류면적이 필요한 것으로 나타난다. 대등한 수위감소값의 홍수저감효과를 발휘하기 위해서 본 연구에서는 On-Line 저류지 면적은 Off-Line 저류지에 비 두배 이상이 필요한 것으로 보여졌다.들에 관한 정보는 종종 현장관측에서 조차 무시되는 경우가 많다. 이에 본 연구에서는 수질모형의 매개변수 중 특히 수리특성에 관련된 매개변수들이 수질에 미치는 영향을 파악하는 것을 목적으로 하고 있다. 이를 위해 적용된 수질모형은 QualKo를 사용하였으며, 대상 하천은 낙동강 본류 경남구간 시점 부근인 회천 합류 전부터 낙동강 본류 경남구간 종점 부근인 밀양강 합류 전까지의 경남 오염총량관리 기본계획 시 구축된 모형 매개변수를 바탕으로 분석을 수행하였다. 일차오차분석을 이용하여 수리매개변수와 수질매개변수의 수질항목별 상대적 기여도를 파악해 본 결과, 수리매개변수는 DO, BOD, 유기질소, 유기인 모든 항목에 일정 정도의 상대적 기여도를 가지고 있는 것을 알 수 있었다. 이로부터 수질 모형의 적용 시 수리 매개변수 또한 수질 매개변수의 추정 시와 같이 보다 세심한 주의를 기울여 추정할 필요가 있을 것으로 판단된다.변화와 기흉 발생과의 인과관계를 확인하고 좀 더 구체화하기 위한 연구가 필요할 것이다.게 이루어질 수 있을 것으로 기대된다.는 초과수익률이 상승하지만, 이후로는 감소하므로, 반전거래전략을 활용하는 경우 주식투자기간

• Korean Journal of Fisheries and Aquatic Sciences
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• v.10 no.4
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• pp.259-265
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• 1977

After a great mortality owing to abnormal oceanographical condition and fungal disease in 1973 hanging cultch lines per raft has been reduced to 450 from 558, and oyster production per raft has also been decreased. It seems to be result of dense culture of oysters and its resulting accumulation of waste materials on the sea bottom in the farm area. The present study was carried out to investigate the effect of rearing density and the degree of eutrophication in Geoje Bay for 6 months from June through November in 1977. Total area of this bay is about $48.9\;km^2$, and the area of registered oyster farms as of November in 1977 is around $10.9\;km^2$, which is about $22.3\%$ of this bay. Water Quality during summer season was shown as transparency 5.5 m, COD 1.5ppm, degree of oxygen saturation $90.6\%$ in upper and middle layers and $82.2\%$ near bottom, chlorophyll-a 3.0 mg/m^3, and phytoplankton $8.7\times10^4\;cells/l$. In superficial mud in August COD was 35.4 mg/g, total sulphide 0.24 mg/g, and phaeophytin $43.7\;{\mu}g/g$dry mud. These values indicate that water qualify in this bay is so far excellent but quantities of chemical oxygen demend and sulphide in bottom mud show maximum level or a little over eutrophication standard.

• Journal of the Korean Wood Science and Technology
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• v.18 no.3
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• pp.26-33
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• 1990

To study the wood quality factors of Populus nigra $\times$ maxmowiczii known a rapidly growing species, the variations of green moisture contents, bulk density, wood fibre dimensions, microfibril angles, and number of leaf knot in stem wood were investigated. The heartwood contained a higher moisture content than the corresponding sapwood. Bulk density in radial patterns variations decrease outward from the pith, then increase toward the bark. The wood-fiber length and diameters had somewhat smaller values than on Populus alba $\times$ glandulosa or Populus euramericana. The microfibril angles decreased rapidly toward the outside, and their mean values were about 16 degree. The grain angles run nearly parallel to the cell axies. Number of leaf knot showed a fluctural change above ground level to a point near the base of the crown and then increased rapidly to the top of tree and average number of leaf knot varied exclusively from tree to tree.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.37 no.4
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• pp.355-360
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• 1992

The experiment was carried out to study the influence of planting densities and fertilizer application levels on some agronomic characters and yield of flower-head in Zingiber mioga ROSC. The results obtained are summarized as follows ; Plant hight was long in dense planting, and short in spacious planting. Stem diameter was thick in spacious planting, and was thin in dense planting. Flower-head weight per plant was decreased in dense planting and was increased in spacious planting. Yield was higher in dense planting densities (10$\times$20 : 50plants /m$^2$, 20$\times$20 : 25plant /m$^2$). Fertilizing (N : P$_2$O$_{5}$ : $K_2$O=15 : 15 : 15kg /10a) was increased than without fertilizing because plant height and number of stem was good.d.

• Journal of the Korean Wood Science and Technology
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• v.10 no.1
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• pp.38-46
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• 1982

The research was carried out to determine the division of juvenile and adult wood from the pattern of variables of wood quality indicators, to investigate general low of the size of juwenile wood and to study the characteristics of juvenile and adult wood. For this study some trees of Pinus koraiensis were selected and several wood quality indicators such as annual ring width. late wood percentage, tracheid length tracheid diameter, wall thicknes, and microfibril angles were measured. The results of this study were summaried as follows. 1) Juvenile and adult wood can be divided into radial variations of wood quality indicators. In this study juvenile wood might be classified as a large fluctuated region of radial wood quality variations in the nearest part to pith. 2) Juvenile wood was indicated as a part of nearly cylinderical shape, averaging 6-11cm in radius, near pith. 3) Number of rings from pith of juvenile wood was about 12-20 and was nearly constant in uniform growth trees among the forest stands. 4) Usually adult wood was formed within the about 5-10m above ground.

• Journal of Korean Society of Forest Science
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• v.36 no.1
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• pp.9-25
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• 1977

As a successive work of the variation studies of natural Pinus densiflora stands, some characteristics of individual trees of the three natural populations selected from the Kwang-won Province, the middle-east part of Korean peninsula, as shown in the location map, were investigated. And the statiscal differences between individuals within population, and between populations were analysed. Twenty trees from each population were selected for this study purpose. Doing this, those trees lagged in growth, usually showing poorer form, were eliminated. The results obtained are summarized as follows: 1. Though the average population ages had the ranage between 50 and 63, the growth of height or diameter was similar. Population No.9 is, however, considered to have better tree forms at glance. Population No.8 showed the heighest value not only in the clear-stem-length ratio. 0.53 but also in the crown-index 0.91. The higher value can be result from those trees having long lateral branches and relatively short crown height, meaning undesirable crown shape. In regard to the fine branchedness and the acuteness of branching angle, the population No.9. is considered to be a better one, whereas there was almost no difference in crown height among populations. 2. Checking the frequency distributions of the ratio of the clear-stem-height to the total height and the crown-indices, some difference between populations are considered. These might be attributed to the previous way of stand mangement which alters the density. 3. In the serration density, the average number of 54 per 1cm needle length, the significant differences exist between individual trees within population but not between populations. A few trees which extremly high serration density were observed. As in serration, so tendencies were in the number of stomata row and resin duct. 4. The population 8 had the resin duct index value of 0.074 as the highest which was twice or triple of the other ones. 5. The patterns of increasing process of the average 10-year-ring-segment were not similar till the 30 years of age, but beyond this, the tendency lines were aggregated. 6. Regading the average summer wood ratio, no diffrence between populations, but in the ranges, i.e. 23 to 30 in population No.8. and 16 to 36 in population No.9., with regad to the specific gravity of wood, there were hardly observed any difference between populations even in the ranges values. As the increase of tree ages, the increase of specific gravity was followed but the increasing patterns were not similar between populations. 7. No significant differences between populations in the average tracheid length and the range were detected. However, the length was increased according to the age increase. The increasing pattern was same between populations.

• Journal of Korean Society of Forest Science
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• v.31 no.1
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• pp.8-20
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• 1976

For study on the variation of natural stand, three populations of Pinus densiflora S. et Z. were selected at samsanri Yongogmyun Myongjugun Kangwondo (4), Hawonri seomyun Uljingun Kyongbuk (5), and Emogdong Suweon Kyongkido (6) successibely after the selection of three population in 1974. Twenty individual trees were chosen from each population and the morphological characteristics of trees, needle and wood properties were investigated on the trees. The results are summerized as follows; 1. Serration density, resin canal number in needle did not show significant differences, however stomata row number in the both sides of needle showed highly significant differences among 3 populations. But significant differences were calculated among individual trees in a population regarding any character of needles. 2. Ail population had high correlation on the stomata row between abaxial and adaxial side of needle. 3. The Myongjungun population showed the highest value of resin duct index, which means the population had the highest degree of hybrid character. 4. The ring segment width and summerwood percentage in the wood properties had significant differences, and yet specific gravity and tracheid length had not significant differences statistically among 3 populations. But all the values were significant statistically among the ring segments within population. 5. The ring segment width decreased rapidly with increasing tree age but summerwood percentage, specific gravity, tracheid length increased slowly to the middle age of tree and then decreased slowly after the age. But the patterns of decrease or increase were some different by population. 6. The values of Uljingun population were generally high in the coefficient of variation on all the needle characters. And the values of Suweon population were always the highest and those of Myongjugun population the lowest in the coefficient of variation on all the wood properties.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.340-346
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• 2002

To understand the characteristics of the passively Q-switched Nd:YAG laser output energy with $Cr^{4+}$:YAG saturable absorbers, the transmissions of $Cr^{4+}$:YAG and the inversion population densities of Nd:YAG at the onset of Q-switch were experimentally analysed. The measured transmissions at the onset of Q-switch were 0.70$\pm$0.02 and 0.62$\pm$0.02 for the 0.48 and 0.38 of initial transmission, respectively. It means that the initial transmission loss of $Cr^{4+}$:YAG absorber is reduced in a low Q-state due to the initial absorbing effect of $Cr^{4+}$:YAG. In pumping stage, $Cr^{4+}$:YAG has absorbing processes due to the fluorescence and amplified spontaneous emissions of the Nd:YAG even if there is no laser oscillation. The minimum population inversion densities for Qswitch were approximately 3.7${\times}{10^{17}}$ and 4.0${\times}{10^{17}}$ $cm^{-3}$, respectively. At the beginning of Q-switch, the number density of $Cr^{4+}$ions in the ground state of $Cr^{4+}$:YAG was approximately 1.4${\times}{10^{17}}$ $cm^{-3}$ and the ratio of the ground to the excited state of absorbing $Cr^{4+}$ions was 0.44 both. The modified theoretical output energies with the initial absorbing effect were 18 and 18.5 mJ. The measured output energies were 17$\pm$1 and 18$\pm$1.5 mJ, respectively. The quantum extraction efficiencies of Q-switch were 0.32 both. The theoretical Q-switched output results with the initial absorbing effect of the saturable absorber are a good agreement with the experimental results.