• 한국축산식품학회지
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• 제39권2호
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• pp.209-221
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• 2019

In this study, the changes in microbial communities of lamb meat packaged in the air (plastic tray, PT) and in a vacuum pouch (VAC) were assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) during the storage at $4^{\circ}C$. For the PT lamb, the total viable count (TVC) was $10^7CFU/g$ on Day 5, and the dominated bacteria were Pseudomonas fragi, P. fluorescens, and Acinetobacter spp. For the VAC lamb, the TVC was $10^7CFU/g$ on Day 9, and the dominated bacteria were lactic acid bacteria, including Carnobacterium divergens, C. maltaromaticum, and Lactococcus piscium. One strain of Pseudomonas spp. also appeared in VAC lamb. The relative abundance of Enterobacteriaceae in VAC lamb was higher than that PT lamb, indicating a more important role of Enterobacteriaceae in spoilage for VAC lamb than that of PT lamb. The microbial compositions changed faster in the lamb stored in a PT than that stored in a VAC, and microbial community compositions of the late storage period were largely different from those of the early storage period for both the conditions. The findings of this study may guide improve the lamb hygiene and prolong the shelf life of the lamb.

• 교육녹색환경연구
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• 제18권1호
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• pp.38-48
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• 2019

본 연구는 대학 연구실 사고 예방을 위해서 실험 전 이루어지는 형식적인 일상점검을 보다 실효성 있는 일상점검표를 제시하는데 목적이 있다. 이를 위해 현재 실시중인 일상점검표와 선행연구자료를 재구성하여, 이를 토대로 2차에 걸친 전문가 델파이 조사로 연구를 실시하였다. 그 결과 연구실 정리정돈 등 일반안전 4개, 기계 및 공구 조임부 이상여부 등 기계기구안전 3개, 전기분전반 주변 적재금지 등 전기안전 3개, 유해인자취급 및 관리대장 비치 등 화공안전 6개, 소화기 점검 등 소방안전 3개, 가스용기 점점 등 가스안전 5개, 손 소독기 관리상태 등 생물안전 1개, 기타 1개, 총 26개 항목을 일상점검표로 제시하였다. 관련 전문가들의 의견을 종합해 보면, 실질적인 일상점검을 위해서는 쉽고 간소화 된 일상점검표가 필요한 것으로 나타났다.

• Yonsei Medical Journal
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• 제59권9호
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• pp.1079-1087
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• 2018

Purpose: Obstructive sleep apnea and chronic obstructive pulmonary disease are independent risk factors of cardiovascular disease (CVD), and their coexistence is known as overlap syndrome (OS). Endothelial dysfunction is the initial stage of CVD; however, underlying mechanisms linking OS and CVD are not well understood. The aim of this study was to explore whether OS can lead to more severe inflammation and endothelial apoptosis by promoting endothelial dysfunction, and to assess the intervention effects of antioxidant tempol. Materials and Methods: Male Wistar rats (n=66) were exposed to normal oxygen [normal control (NC) group], intermittent hypoxia (IH group), cigarette smoke (CH group), as well as cigarette smoke and IH (OS group). Tempol intervention was assessed in OS group treated with tempol (OST group) or NaCl (OSN group). After an 8-week challenge, lung tissues, serum, and fresh blood were harvested for analysis of endothelial markers and apoptosis. Results: The levels of intracellular adhesion molecule-1, vascular cellular adhesion molecule-1, and apoptosis in circulating epithelial cells were the highest in OS group and the lowest in NC group. These levels were all greater in IH group than in CH group, and were lower in OST group than in OS and OSN groups (all p<0.001). Conclusion: Synergistic effects of IH with cigarette smoke-induced emphysema produce a greater inflammatory status and endothelial apoptosis. OS-related inflammation and endothelial cell apoptosis may play important roles in promoting cardiovascular dysfunction, and antioxidant tempol could achieve a partial protective effect.

• Composites Research
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• 제34권2호
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• pp.108-114
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• 2021

일반적으로 그래핀 플레이크는 산화그래핀을 화학적 또는 열적 환원 공정을 통해 환원그래핀으로 변환하여 대량 생산하고 있다. 그래핀 플레이크는 다양한 형태로 응용되는데, 그 중 진공여과를 이용한 적층 공정을 통해 종이형 필름으로 제작이 가능하다. 그래핀 종이는 신축성이 부족한 단점이 있어 신축성 소자 응용에 제약이 있다. 본 연구에서는 신축성이 있는 그래핀 종이를 제작하기 위하여, 그래핀 종이에 주름을 만들었다. 신축성이 뛰어난 접착 필름을 미리 늘린 후, 그 위에 그래핀 종이를 붙이고, 접착 필름을 원래 상태로 놓아 주어 그래핀 종이에 주름을 만들었다. 이 때, 접착 필름에 가하는 당김 정도 및 젖은 상태에 따라 주름의 형상이 변하는 것을 실험적으로 관찰하였다. 특히, 그래핀 종이와 접착 필름의 전단 탄성 계수 차에 의하여 주름의 주기가 바뀌는 현상을 관찰하였다.

• 한국산학기술학회논문지
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• 제22권2호
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• pp.644-650
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• 2021

본 연구는 지구 온난화의 주요 원인인 이산화탄소를 이용하여 메탄의 개질반응 특성을 수행하였다. 이산화탄소와의 메탄 분해 반응을 전이금속 촉매인 주석을 사용하여 수행되었으며, 주석의 분해 반응성은 니켈, 철과 같은 전이 금속보다 낮으며, 대부분의 분해 반응은 고체 상태 촉매하에 수행된다. 반면에 주석의 녹는점은 505.03K로 액상 촉매하에서 분해가 발생된다. 주석을 사용하는 경우 액상으로 반응하며 메탄이 분해되어 생성되는 고체상 탄소가 촉매에 침적되어 비활성화되는 것을 것을 방지하는 장점이 있다. 이산화탄소를 사용하여 메탄을 분해하는 경우 일산화탄소와 수소를 생성한다. 촉매의 활성과 수명을 높이기 위해 Ni를 사용한 경우 촉매 활성이 향상되었다. 본 연구에서는 과잉습식함침법을 이용하여 촉매를 합성하였으며, 반응 온도, 공간 속도에 따른 활성과 촉매 재생 가능성을 타진하였다. 탄소가 침적된 주석의 촉매 재생 온도는 1023 K로 나타났으며, 니켈을 조촉매로 사용하고 물을 공급하므로써 반응성이 향상되는 것으로 나타났다.

• 한국지반공학회논문집
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• 제36권12호
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• pp.69-76
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• 2020

Back-to-Back 보강토옹벽은 좁은 구간에 양립하는 옹벽의 형식을 가지기 때문에 벽체간의 이격거리에 따라 보강재가 겹치게 되어 보강재 간의 상호작용에 의한 응력 변화와 일체화된 상태에서 전체가 거동하는 문제 등으로 설계단계에서 신중한 접근이 필요하나 현재 국내에 정형화된 설계기준이나 지침이 전무한 상태이다. 본 연구는 이러한 Back-to-Back 보강토옹벽에 대해 옹벽폭 대 높이비(옹벽폭비, Wb/H)에 따른 최적 보강길이비에 대해 고찰하였다. 옹벽폭비는 FHWA 설계기준의 Case II에 해당하는 1.1H, 1.4H, 1.7H, 2.0H, 높이는 일반적으로 가장 많이 적용되고 있는 3.0m, 5.0m, 7.0m, 10.0m를 대상으로 하였으며, 각 조건에서 수치해석을 통해 FHWA 설계기준의 적정성과 옹벽의 높이 및 옹벽폭비에 따른 최적 보강길이비를 제안하였다.

• 한국물환경학회지
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• 제27권4호
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• pp.445-460
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• 2011

The objective of this study was to construct and assess the applicability of the EFDC model for Saemangeum Reservoir as a 3D hydrodynamic and water quality modeling tool that is necessary for the effective management of water quality and establishment of conservation measures. The model grids for both reservoir system only and reservoir-ocean system were created using the most recent survey data to compare the effects of different downstream boundary conditions. The model was applied for the simulations of temperature, salinity, water quality variables including chemical oxygen demand (COD), chlorophyll-a (Chl-a), phosphorus and nitrogen species and algal biomass, and validated using the field data obtained in 2008. Although the model reasonably represented the temporal and spatial variations of the state variables in the reservoir with limited boundary forcing data, the salinity level was underestimated in the middle and upstream of the reservoir when the flow data were used at downstream boundaries; Sinsi and Garyuk Gates. In turn, the error caused to increase the bias of water quality simulations, and inaccurate simulation of density flow regime of river inflow during flood events. It is likely because of the loss of momentum of sea water intrusion at downstream boundaries. In contrast to flow boundary conditions, the mixing between sea water and freshwater was well reproduced when open water boundary condition was applied. Thus, it is required to improve the downstream boundary conditions that can accommodate the real operations of the sluice gates.

• Current Applied Physics
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• 제18권12호
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• pp.1577-1582
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• 2018

While controlling the cation contents in perovskite rare-earth nickelate thin films, a metal-to-insulator phase transition is reported. Systematic control of cation stoichiometry has been achieved by manipulating the irradiation of excimer laser in pulsed laser deposition. Two rare-earth nickelate bilayer thin-film heterostructures with the controlled cation stoichiometry (i.e. stoichiometric and Ni-excessive) have been fabricated. It is found that the Ni-excessive nickelate film is structurally less dense than the stoichiometric film, albeit both of them are epitaxial and coherent with respect to the underlying substrate. More interestingly, as a temperature decreases, a metal-to-insulator transition is only observed in the Ni-excessive nickelate films, which can be associated with the enhanced disproportionation of the Ni charge valence. Based on our theoretical results, possible origins (e.g. anti-site defects) of the low-temperature insulating state are discussed with the need of future work for deeper understanding. Our work can be utilized to realize unusual physical phenomena (e.g. metal-to-insulator phase transitions) in complex oxide films by manipulating the chemical stoichiometry in pulsed laser deposition.

• Journal of Ceramic Processing Research
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• 제19권6호
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• pp.461-466
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• 2018

The effects of Ca/Sr ratio and the sintering temperature on the properties of $(Ca_xSr_{(1-x)})ZrO_3$ (CSZ) ceramics were investigated in this study. CSZ ceramics were prepared using solid-state reaction process, which were sintered in air at temperatures ranging from $1350^{\circ}C$ to $1450^{\circ}C$. Their structures were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The change in Ca/Sr ratio significantly affected the crystalline phase and the dielectric properties of the $(Ca_xSr_{(1-x)})ZrO_3$ ceramics. The secondary phase, $Ca_{0.15}Zr_{0.85}O_{1.85}$, was observed and increased correspondingly with the rising of sintering temperatures. In order to understand the effects of secondary phase on the dielectric properties of CSZ ceramics, the $Ca_{0.15}Zr_{0.85}O_{1.85}$ phase was prepared individually using solidstate method. The $Ca_{0.15}Zr_{0.85}O_{1.85}$ ceramics sintered at $1500^{\circ}C$ for 2 hours possessed a dielectric constant (${\varepsilon}_r$) of 21.7, a dielectric loss ($tan{\delta}$) of $49.510^{-4}$ and an Insulation Resistance (IR) of $2.1{\times}10^{10}{\Omega}$. The ($Ca_{0.7}Sr_{0.3})ZrO_3$ ceramics exhibited the best dielectric properties, with a permittivity of 29, a dielectric loss ($tan{\delta}$) of $2.7{\times}10^{-4}$, and an Insulation Resistance (IR) of $2.6{\times}10^{12}{\Omega}$.

• 대한금속재료학회지
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• 제48권3호
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• pp.262-267
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• 2010

$LiNi_{1-x}Mg_xO_2$(x=0, 0.025, 0.05, 0.075, 0.1) samples were synthesized by the solid-state reaction method. The crystal structure was analyzed by X-ray powder diffraction and Rietveld refinement. $LiNi_{1-x}Mg_xO_2$samples give single phases of hexagonal layered structures with a space group of R-3m. The calculated cation-anion distances and angles from the Rietveld refinement were changed with Mg contents in $LiNi_{1-x}Mg_xO_2$. The thicknesses of $NiO_2$ slabs were increased and the distances between the $NiO_2$ slabs were decreased with the increase in Mg contents in the samples. The electrical conductivities of sintered $LiNi_{1-x}Mg_xO_2$ samples were around $10^{-2}$ S/cm at room temperature. The electrochemical performances of $LiNi_{1-x}Mg_xO_2$were evaluated by coin cell test. Compared to $LiNiO_2$, $LiNi_{0.95}Mg_{0.05}O_2$ exhibited improved high-rate capability and cyclability due to the well-ordered layered structure by doping of Mg ion.