• Economic and Environmental Geology
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• v.31 no.3
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• pp.265-271
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• 1998

In the hydrologic and hydrochemical studies of natural waters, oxygen and hydrogen isotope compositions of waters are very important to elucidate the origin and circulation pattern of water in the hydrologic system. The hydrogen isotope analysis of waters usually has been undertaken through the reduction of water to form hydrogen gas using pure metals (in general, zinc and uranium). In 1996, a new apparatus (H/Device) was developed to prepare the water samples (by the reduction with Cr metal) without some intrinsic problems that may yield incorrect and/or inaccurate data, and was installed at 1997 in the Center for Mineral Resources Research (CMR) in Korea University. However, the optimistic conditions of preparation and analysis of samples has not been established. In this paper, we introduce the efficiency of H/Device to obtain accurate hydrogen isotope values of water, and discuss both the optimum conditions including the effective reduction time and the probable mixing (memory) effect between successive samples. We obtained large amounts of a laboratory working standard (KUW; Korea University Water) with the average ${\delta}D_{SMOW}$ value of $-42.1{\pm}1.0$‰ $(1{\sigma})$.

• Journal of Korea Foundry Society
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• v.17 no.5
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• pp.472-479
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• 1997

The effect of size and mass fraction of SiC particulate on the fatigue and wear have been investigated for semi-liquid formed SiCp/AZ91HP Mg composites. In the study, different particulate sizes of 7, 20, $50 {\mu}m$ were prepared with various mass fraction for sample preparation. By tension-tension fatigue tests, whose procedures are standardized in ASTM standard 647E-93, the da/dN vs. ${\Delta}K$ curves were obtained. Also, the crack propagation paths were observed by optical microscope. As a result of wear test, specific wear loss is decreased with increasing mass fraction and particulate size. Specific wear loss of 30 mass% $50 {\mu}m$ SiC reinforced Mg composite is compared to SKD11.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.490-491
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• 2007

We have investigated dielectric polarization in organic light-emitting diodes using 8-hydroxyquinoline aluminum$(Alq_3)$ as an electron transport and emissive material. We analyzed the dielectric polarization of organic light emitting diodes using impedance. Impedance characteristics was measured complex impedance Z and phase ${\theta}$ in the frequency range of 40Hz to $10^8Hz$. We obtained dielectric constant and loss tangent (tan ${\delta}$) of the device. From these analyses, we are able to interpret a dielectric dispersion and dielectric absorption contributed by an interfacial and orientational polarization.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.381-383
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• 2005

바이오센서 응용을 위한 대칭 및 비대칭 마하젠더 간섭계 광도파로 소자의 설계, 제작 및 광학적 응답특성을 평가하였다. 설계 제작된 광도파로 소자의 압력광원은 각각 1550nm와 632.8nm이고, 코어와 클래딩의 굴절률차는 0.45 $\Delta$%로 설계 제작하였다. 센서부(상위 클래드)의 금 박막의 미소 굴절률 변화에 따른 TE, TM모드의 특성을 분석하였다. 센서의 보다 높은 감도 개선을 위한 나노-광자결정 구조가 주목받고 있는데, 광자결정 구조의 구현를 위한 리소그래피 공정은 높은 분해능과 신뢰성 있는 나노스케일의 공정이 요구된다. 광-바이오센서의 감도 개선을 위해 센서부 표면에 2차원 나노-광자결정 배열을 제안하고 이를 구현하기 위한 Dip-Pen Nanolithography 공정에 대해 고찰하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.100-103
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• 2005

Homogeneously aligned nematic liquid crystal modes are representatively the -FFS (fringe-field switching) mode using liquid crystal (-LC) with negative dielectric anisotropy, the +FFS mode and the IPS (in-plane switching) mode using +LC with positive dielectric anisotropy. In view of image quality evaluation standard of LCD, we compared characteristics of the brightness, the contrast ratio (CR) and color shift when the modes have respectively optimized phase retardation values $(d{\Delta}n)$. Consequently, in the most sensitively viewing angle of a man's physical vision, both FFS modes have advantage over the IPS mode from the brightness & the CR point of view. We are also confirmed that the +FFS mode out of them shows the smallest color shift according to all viewing directions in grey levels.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.556-556
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• 2012

본 연구는 수지상, 망상, 분기상 등을 모의 할 수 있는 1차원 고정확도 하천흐름 해석 모형을 개발하는데 그 목적이 있다. 이러한 복잡한 형태의 하천흐름 해석 모형 개발을 위해 기존 Fread(1973)가 수지상 하천흐름 해석을 위해 개발한 바 있는 Relaxation 알고리듬을 활용하였으며 이를 망상 및 delta 등에 적용할 수 있도록 확장하였다. 모형의 검증을 위해 한강 팔당댐 하류 한강대교 노들섬 지점에서 발생되는 유량 분기 현상을 모의하였다. 모의구간은 팔당댐~행주대교 구간이며, 대상호우는 2011년 8월 발생한 사상이다. 대상구간 내 팔당대교, 잠수교, 한강대교 수위관측소의 수위자료를 활용하여 조도계수 보정을 수행하였다. 한강대교 노들섬 구간에 대하여 망상하도를 구성하였으며 한강대교 남단과 북단에서 운영 중인 ADVM 유량관측 자료와 본 연구모형의 모의 결과를 비교 검토하였다. 추가로 HEC-RAS 모형의 입력자료를 구성하여 모의하였으며 이를 본 연구모형의 결과와 비교하였다. 이를 통해 본 연구 모형의 하도망 해석 알고리듬의 타당성을 입증하였다. 따라서 본 연구모형을 통해 복잡한 하도로 구성되는 하천 하구 지역의 흐름현상 규명이 가능할 것으로 판단된다.

• Kyungpook Mathematical Journal
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• v.56 no.1
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• pp.185-220
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• 2016

We study the Gauss and Poisson semigroups connected with the Riemann-Liouville operator defined on the half plane. Next, we establish a principle of maximum for the singular partial differential operator $${\Delta}_{\alpha}={\frac{{\partial}^2}{{\partial}r^2}+{\frac{2{\alpha}+1}{r}{\frac{\partial}{{\partial}r}}+{\frac{{\partial}^2}{{\partial}x^2}}+{\frac{{\partial}^2}{{\partial}t^2}}};\;(r,x,t){\in}]0,+{\infty}[{\times}{\mathbb{R}}{\times}]0,+{\infty}[$$. Later, we define the Littlewood-Paley g-function and using the principle of maximum, we prove that for every $p{\in}]1,+{\infty}[$, there exists a positive constant $C_p$ such that for every $f{\in}L^p(d{\nu}_{\alpha})$, $${\frac{1}{C_p}}{\parallel}f{\parallel}_{p,{\nu}_{\alpha}}{\leqslant}{\parallel}g(f){\parallel}_{p,{\nu}_{\alpha}}{\leqslant}C_p{\parallel}f{\parallel}_{p,{\nu}_{\alpha}}$$.

• Journal of Magnetics
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• v.18 no.1
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• pp.30-33
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• 2013

The magnetocaloric effect and magnetization behavior have been analyzed in the double-perovskite $La_{0.7}Ba_{0.3}Mn_{1-X}Fe_XO_3$ compound with the sintering temperature at 1273 K. Samples were fabricated by the conventional solid-state reaction method. X-ray diffraction measurement revealed that all the samples had a single phase in orthorhombic. Detailed investigations of the magnetic entropy behavior of the samples were discussed with the variation of $T_C$. The magnetic entropy changes, ${\Delta}S_M$ of approximately 0.36-1.14 J/kg K were obtained in the temperature range of 145-350 K for the $La_{0.7}Ba_{0.3}Mn_{1-X}Fe_XO_3$ compound. The enhancement of the magnetic entropy change is believed to be due to changes in the microstructure, which changes the magnetic part of the entropy of a solid around the magnetic ordering temperature.

• Journal of Gastric Cancer
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• v.22 no.3
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• pp.248-259
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• 2022

Purpose: To overcome the technical difficulties of single-incision laparoscopic distal gastrectomy (SILDG), needle grasper (Endo Relief^TM)-assisted SILDG (NASILDG) was developed. Here, we compared the operative convenience and postoperative outcomes between SILDG and NASILDG. Materials and Methods: A needle grasper was inserted into the right upper abdomen and used in the NASILDG. We retrospectively reviewed patients who underwent D1 + dissection and delta-shaped Billroth I anastomosis with SILDG or NASILDG performed by a single surgeon between September 2015 and August 2018. Results: The SILDG (male, 50.0%) and NASILDG (male, 60.0%) groups included 10 and 15 patients, respectively. The operative time without combined operation and anastomosis was significantly shorter in the NASILDG group. Early complications and scar characteristics were not significantly different between the two groups. Conclusions: By adding a needle grasper, SILDG became more convenient without decreasing cosmetic results. NASILDG could be a recommended method to reduce the technical difficulty of SILDG.

• Steel and Composite Structures
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• v.53 no.1
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• pp.1-27
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• 2024

This work presents the effectiveness of differential quadrature shape functions (i.e., Lagrange interpolation polynomial, Cardinal sine function, Delta Lagrange kernel and Regularized Shannon kernel) in the solution of nonlinear vibration of multilayers piezoelectric plates with nonlinear elastic support. A piezoelectric composite laminated plate is rested on nonlinear Winkler and Visco-Pasternak elastic foundations problems. Based on 3D elasticity theory and piezoelectricity, the governing equations of motion are derived. Differential quadrature methods based on four shape functions are presented as numerical techniques for solving this problem. The perturbation method is implemented to solve the obtained nonlinear eigenvalue problem. A MATLAB code is written for each technique for solving this problem and extract the numerical results. To validate these methods, the computed results are we compare with the previous exact results. In addition, parametric analyses are offered to investigate the influence of length to thickness ratio, elastic foundation parameters, various boundary conditions, and piezoelectric layers thickness on the natural frequencies and mode shapes. Consequently, it is discovered that the obtained results via the proposed schemes can be applied in structural health monitoring.