• The Korean Journal of Applied Statistics
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• v.6 no.2
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• pp.247-252
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• 1993

Consider minimizing the sum of absolute deviations for multiple regression models. If a regression line is assumed to pass a given point, then we can find that the $L_1$ regression coefficient can be defined in terms of the weighted medians of the slopes from each data point to the given point. Therefore, $L_1$ method could be regarded to find the optimal point which regression line passes over.

• School Mathematics
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• v.14 no.4
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• pp.409-429
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• 2012

This paper reports the process two 11th grade students went through in reinventing derivatives on their own via a context problem involving the concept of velocity. In the reinvention process, one of the students conceived a tangent line as the limit of a secant line, and then the other student explained to a peer that the slope of a tangent line was the geometric mean of derivative. The students also used technology to concentrate on essential thinking to search for mathematical concepts and help visually understand them. The purpose of this study was to provide meaningful implications to school practices by describing students' process of reinvention of derivatives. This study revealed certain characteristics of the students' reinvention process of derivatives and changes in the students' thinking process.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.04a
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• pp.221-224
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• 2003

이 연구는 국내의 균열암반에 대한 지하수 유동 연구가 대수층이 등방이라는 가정하에 진행피고 있는 방법에서 벗어나 대수층이 이방성을 띤다는 가정하에 대수층의 수리적 이방성을 해석하는데 중점을 두었다. 수리시험은 30.91 $m^3$/day로 BH-1공에서 300분간 양수였으며, 각각의 관측공 BH-2, BH-3, BH-4, 및 BH-5공에서 시간에 따른 수위강하를 관측하였다. 수리시험에 의해 얻어진 시간별 수위강하 자료를 이용하여 Jacob(1950)의 직선법에 의해서 직선의 기울기(m)와 수위강하가 영이 되는 지점에서의 시간( $t_{0}$)을 계산하였다. 대수층의 수리학적 이방성 텐서 (tensor) 즉, 최대투수량계수텐서 ( $T_{ξξ}$)와 최소투수량계수텐서 ( $T_{ηη}$)를 산출하기 위해서 Stewart(1973)에 의해서 정립된 정규최소제곱(Ordinary least-square)방법을 적용하였으며, 이 방법은 관측공이 최소한 4개를 필요로 한다. 그 결과로, $T_{ξξ}$는 12.21 $m^2$/day이고 $T_{ηη}$는 10.47 $m^2$/day로 산출되었다. 최대투수량계수텐서의 방향은 Nl9.13$^{\circ}$E 이고 이방성율은 1.17로 산출되었다. BH-1공에서 수리시험시 대수층의 이방성은 등방성에 가깝게 표현되었다. 이는 연구지역 대수층이 다수의 균열에 의해서 수리적 상호연결성이 고루 분포된 것으로 판단된다.

• Journal of Biomedical Engineering Research
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• v.18 no.4
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• pp.499-505
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• 1997

A non-invasive technique to measure absorption and scattering coefficients was investigated The reflected backscattered light from the surface of phantom and biological tissue was obtained by using a time-correlated single photon counting system in pico-second time domain. The absorption and scattering coefficients were acquired by the time of peak and asymptotic behavior of the time-resolved reflectance curve and agreed well the ones that is obtained with deconvolution method It was found that the approximation method was good for biological medium to calculate optical properties due to its convenience and accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.515-527
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• 2014

This study conducted experiment for understanding engineering characteristics of domestic sands by examining standard sand and sand from Yokji Island and Nakdong River in terms of confining pressure, $K_0$, over consolidation and relative density factors through triaxial compression test. The test showed that deviator stress by strain positively changed as confining pressure and relative density grow while $K_0$ and over consolidation factors do not directly correlated with it. Angle of internal friction decreases as confining pressure increases which strengthens contact force between particles, and declines as relative density drops, whereas $K_0$ and over consolidation factors hardly affect the results. When it comes to volumetric strain, volume expansion decreases as confining pressure increase due to crushability and rearrangement of particles while $K_0$ and over consolidation shows same movement unconditionally, and relative density appears compressed as it grows at the beginning however it expands as axial strain increases. Modulus of elasticity ($E_{sec}$) by strain has tendency into convergence resulting in initial secant modulus of elasticity ($E_{ini}$) > secant modulus of elasticity($E_{sec}$) > tangent modulus of elasticity ($E_{tan}$). On the other hand, it grows as confining pressure and relative density increase while indicating similar modulus of elasticity ($E_{sec}$) regarding on $K_0$ and over consolidation. Slope of critical line (M) tended to decrease as confining pressure increases, follow same line according to $K_0$, confining pressure and relative density, and increase as relative density grows.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.3
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• pp.213-221
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• 2007

In response to anthropogenic global warming due to a buildup greenhouse gas, the effect of the air temperature on water temperature has been noticed and some efforts have been made to build an air/water temperature relationship at the Masan Bay area by the Ministry of Maritime Affairs & Fisheries (MOMAF). As a result of analyzing the auto- and cross-correlation coefficient between air/water temperature, high correlation $(\sim0.9)$ is shown and the correlation coefficient of air temperature is higher than that of water temperature at the lag time less than approximately 10 days. Separate functions are fitted to the air/water relationship at the Masan Bay to take hysteresis into account. The slopes of the straight line for the rising limb are 0.829 and 0.774 for MA1 and MA2 station respectively, while 1.385 and 1.444 ($\sim1.75$ times larger) for the falling limb. Consequently, the seasonal hysteresis should be considered in order to determine an air/water relationship and accurately estimate the water temperature using the air temperature at Masan Bay.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1A
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• pp.19-24
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• 2011

Concrete columns strengthening effect due to FRP (Fiber Reinforced Polymer) confinement depends on the elastic modulus of the FRP. This study analyzes the retrofitting effect of FRP confinements according to elastic modulus of FRPs using the existing data and suggests a practical model to assess the strengthening effect. This study subdivides the FRP elastic modulus into three parts based on normal concrete and steel elastic modulus. The slope and the y-axis intersection seem to increase with increasing FRP elastic modulus. In addition, the strengthening effect does not develop up to some amount of FRP confinement having relatively smaller elastic modulus than the compressive elastic modulus of concrete. In this case, a linear model to assess the strengthening effect is hard to be used. Thus, this study suggests that the FRP jackets having 2 times larger elastic modulus than that of concrete are recommended to be used for retrofit of concrete and that a linear model can be applied for the case. The suggested model shows nearly the same result regardless to the restraint of the y-axis intersection. This has been observed at the model of steel confinement and, thus, is a reliable result.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.61-66
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• 1999

반복 응력 상태 아래서 알루미나 세라믹의 피로 표면손상 누적현상이 분석되었다. 연속 미끄럼 접촉 시에 발생하는 응력 상태를 재현하기 위해서 동시에 작용하는 수직-수평 반복 압축하중 기법이 사용되었다. 알루미나 구와 평판의 접촉면에서 알루미나 미세 결정의 피로 파손에 의한 마모 입자 형성 기구가 관찰되었고, 반복하중의 횟수와 수직-수평 하중비가 커질수록 마모량은 증가하였다. 반복 접촉하중에 의한 표면손상 누적이 접촉 수직 변위 측정으로 정량화 되었다. 두 접촉 구조물의 강성 (하중-변위 선도의 기울기) 변화가 두 재질의 탄성계수의 변화로 표현되었다.

• The Transactions of the Korean Institute of Power Electronics
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• v.4 no.2
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• pp.184-191
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• 1999

일반적으로 시스템 인식과 제어를 위해 이용하는 다층망 신경회로망은 기존의 역전파알고리즘을 이용한다. 그러나 결선강도에 대한 오차의 기울기를 구하는 방법이기 때문에 국부적 최소점에 빠지기 쉽고, 수렴속도가 매우 늦으며 초기결선강도 값들이나 학습계수에 민감하게 반응한다. 이와 같은 단점을 개선하기 위해 본 논문에서는 칼만필터링 기법을 도입하여 수렴속도를 빠르게 하고 초기 결선강도의 영향을 받지 않도록 개선하였으며, 유도전동기의 속도추정과 제어에 적용하여 좋은 결과를 보였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1271-1281
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• 2000

본 논문에서는 모드 매칭법과 일반 산란계수법을 이용하여 경사진 금속봉이 도파란내에 놓여 있을 때 반사 특성과 투과 특성을 구하였으면, 이 결과를 이용하여 동축선로와 도파관과의 접합에 응용할 수 있도록 최적의 조건을 도출하였다. 여기서 반사특성은 기울기사 클수록 뚜렷아세 개선되어서 최소-40dB까지 감소하였고, 투과특성은 최적의 각도 45$^{\circ}$에서 최대의 특성을 얻을 수 있었다. 또한, 이를 HFSS의 결과와 비교하였을 때 잘일치하는 결과를 얻을 수 있었다.