• The Korean Journal of Pesticide Science
• /
• v.17 no.1
• /
• pp.1-5
• /
• 2013

This study was conducted to the amount of pesticide residue in 21 different kinds of 100 commercial flowering teas. Multi-residue analyses of 203 pesticides was performed using the GC-ECD, GC-NPD, GC-MSD, and LC-MS/MS. Pesticide residues were detected in 4 samples (4%) of which 4 samples (4%) violated the maximum residue limits. 4 samples violating the limit were all imported teas. Pesticides detected were chlorpyrifos, flufenoxuron, lufenuron, pyrimethanil and methoxyfenozide. These results indicate the need of continuous monitoring of pesticide residue needs for safety of flowering teas.

• Journal of Ocean Engineering and Technology
• /
• v.12 no.1
• /
• pp.143-152
• /
• 1998

해안구조물 설치시 기초지반의 안정성 해석을 위한 파랑에 기이한 액상화 메카니즘을 과잉간극수압(excess pore pressure) 현상과 관련하여 논의하였다. 과잉간극수압 발생 메커니즘에 있어서 두 가지 형태, 즉 변동과잉간극수압 (Oscillatory excess pore pressure) 및 잔류과잉간극수압 (Residual excess pore pressure) 각각에 기인한 액상화의 특성을 구명하였다. 또한, 과잉간극수압 및 해저지반의 액상화 가능성에 대한 평가공정을 제시하였는데 이는 모형실험과 현장관측자료에 의해 그 적용성이 검증되었다. 이러한 평가공정(Assessment Procedures)은 투수성 해저/기초 지반의 액상화를 추정하는데 이용될 수 있다. 해안구조물 기초 설계 및 해저 지반의 안정성 평가시 액상화의 가능성 또는 과잉간극수압의 적절한 평가.고려가 무엇보다 중요하다고 사료된다.

• Korean Journal of Optics and Photonics
• /
• v.9 no.3
• /
• pp.142-145
• /
• 1998

It is shown that the optical system with Gaussian pupil e, diffraction amplitude distribution is not affected by the presence of residual aberrations. The case of spherical aberration is treated, as an example, and the complex diffraction amplitude distribution at the neighbourhood of the image point is described analytically by using a recurrence formula.

• Journal of the Korean Society for Precision Engineering
• /
• v.25 no.11
• /
• pp.100-106
• /
• 2008

We have studied the characteristic changes of optical device using imprint lithography. An imprinted structure is inherently involved in residual stress due to the temperature and the pressure cycle during fabrication process. A structure with residual stress undergoes stress relaxation, which leads io dimensional change. Therefore, annealing processes was performed to reduce the residual stress of imprinted polymer channel. Reduction of residual stress was confirmed through dimensional change, birefringence, and the mechanical properties. We have fabricated an optical device, and it saw the optical intensity changes within 0.1% for 1 month.

• Journal of Digital Contents Society
• /
• v.8 no.3
• /
• pp.385-391
• /
• 2007

In this paper, we propose a frequency synchronization algorithm for S-DMT cable modem, which is practicable to the next-generation high capacity upstream physical layer in HFC networks. Analyzing several viable frequency synchronization algorithms of multicarrier systems, we proposed an algorithm using predetermined training sequence of repeated pattern in preamble field and residual frequency offset compensation with pilot signals. We verified that the simulation results of the proposed algorithm in AWGN showed good performance and suitability to the S-DMT upstream cable modem for fast frequency synchronization.

• Journal of the KSME
• /
• v.28 no.4
• /
• pp.322-327
• /
• 1988

용접구조물의 파괴는 단순 역학적인 차원을 넘어서 재료공학적 검토와 시공상의 각종 변수를 고려해야만 정확하게 이해할 수가 있으며 방지할 수 있다. 용접도중에 발생되는 미소파괴(균열) 는 적절한 재료의 선정과 적당한 시공법으로 해결할 수 있으며, 사용도중 발생되는 거시적 파 괴는 사용조건에 유의하고 발생된 용접결함을 제거할 수 있다면 방지할 수 있다. 결론적으로 용접구조물의 파괴는 용접도중에 결함을 발생시키지 않는 방법으로 방지하는 것이 가장 효과적 이기 때문에 시공법의 선정 및 실시는 충분한 검토와 주의가 필요하다. 용접품의 파괴현상을 해석하는 데는 현재까지 잘 연구되어진 각종 파괴역학적 및 피로역학적 해석이 적용될 수 있 으나 용접부의 불균일한 조직형성에 따른 기계적 성질의 불균일성과 잔류응력 등을 추가로 고 려해야 하는 것이 약간 다를 뿐이다. 현재 용접부의 취성 및 피로파괴에 대한 다방면의 연구가 활발하게 이루어지고 있는 형편이며 향후에는 용접구조물의 수명예측을 포함한 가족 파괴해석 기술이 확립될 것으로 생각된다.

• Journal of the KSME
• /
• v.28 no.4
• /
• pp.313-321
• /
• 1988

어떤 구조물이 반복하중을 받으면 피로파괴를 일으킨다. 만일 이 구조물이 부식환경 속에 앗 으면 불활성 분위기나 공기 중에서 보다 빨리 파괴에 이르게 된다. 이러한 현상을 흔히 부식 피로라고 한다. 부식피로에 크게 영향을 미치는 변수들을 대략 기계적 변수, 금속학적 변수, 환경 변수로서, 기계적 변수에는 최대응력 확대계수, 응력확대계수범위, 응력비, 반복하중 주파수, 반복하중파형, 응력상태, 잔류응력, 균열의 크기 및 모양 등이 있으며 금속학적 변수로는 합금 조성, 합금원소와 불순물의 분포, 미세조직과 결정구조, 열처리, 소성가공, 집합조직 등이며 환 경변수에는 온도, 환경의 형태(기체, 액체), 부식성분의 분압 또는 농도, 전기화학적 전위, pH, 수용성 환경의 점성, 피복, 부식억제제 등이 있다. 이와 같이 부식환경 속에 있는 구조물의 파 손을 이해하기 위하여는 응력부식과 부식피로를 공부하여야 한다. 이 현상은 매우 복잡한 문 제이기 때문에 아직도 완전히 이해되지 않은 상태이고 따라서 중요한 연구대상이 되고 있다. 여기서는 응력부식과 부식피로의 파괴역학적인 측면을 소개하고자 한다.

• Journal of the Korean Geophysical Society
• /
• v.2 no.3
• /
• pp.191-200
• /
• 1999

Analysis of chirp high-resolution seismic profiles from the central Yellow Sea reveals that depositional environments in this area can be divided into three distinctive zones from west to east: (1) subaqueous delta system near the Shandong Peninsula, (2) erosional zone in the central Yellow Sea, and (3) tidal sand ridges and sand waves near the Korean Peninsula. The Shandong subaqueous delta, extending southward from the Shandong Peninsula, changes gradually into prodelta southeastward. The sediments originated from the Yellow River are transported southward along the Chinese coastal area. The erosional zone in the central Yellow Sea contains numerous paleochannels and shows linear erosional features trending northwest-southeast. The erosional zone would be dominated by non-depositional or erosional processes during the Holocene. Tidal sand ridges and sand waves are well developed along the western coast of Korea. The residual sands, which were originally fluvial sediments at the sea-level lowstand, are interpreted as the result of winnowing process during the sea-level rise. Modern sand ridges generally migrates in a northeast-southwestern direction, which coincide with dominant tidal current direction.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.3
• /
• pp.132-145
• /
• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

• Journal of the Korean Wood Science and Technology
• /
• v.33 no.4 s.132
• /
• pp.30-37
• /
• 2005

Heating and Steaming treatments were carried for deresinning and color change of radiata pine juvenile wood. The boards of 20 mm and 30 mm thicknesses were heat-treated at $150^{\circ}C$ and $220^{\circ}C$ for 2, 4 and 6 hours and steamed at $100^{\circ}C$ for 6, 24 and 48 hours. For extracting residual resin in treated boards and measuring wood surface color, alcohol-benzene solution and a portable colorimeter were used, respectively. The board of 20 mm thickness were deresined effectively by heating at over $150^{\circ}C$ for 2 hours or steaming for 6 hours while that of 30 mm thickness by steaming for 48 hours. For the board of 30 mm thickness treatment time was more influencing on deresinning than treatment temperature. The steamed boards showed higher $L^*$ than the heat-treated for both thicknesses. $L^*$ decreased with the increase of treatment temperature and time, but for the board heat-treated at $220^{\circ}C$ it didn't change after 4 hours. The surface color of the boards heat-treated at $220^{\circ}C$ for 4 and 6 hours were obviously changed, but those at $150^{\circ}C$ were not. It was revealed that the core of the heat-treated board was color changed as well as the surface.