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단순공정으로 제작된 마이크로/나노 하이브리드 채널의 불균형 동전기성을 이용한 미세혼합기 연구
유사무엘(Samuel Yu),김선민(Sun Min Kim) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.4
본 연구에서는 미세채널과 나노채널의 교차부에 불균형 동전기성을 이용한 미세혼합기를 개발하였다. 채널 내 용액의 혼합은 인가된 전압에 의한 전기삼투유동과 미세채널과 나노채널 교차 부에서의 불균형 동전기성에 의한 와류현상에 의해 이루어진다. 미세채널은 PDMS 을 이용하여 소프트리소그래피 공정으로 제작하였고, 나노채널은 미세채널의 특정위치에 전기적 충격에 의한 PDMS 의 파괴로 매우 간단하게 제작하였다. 혼합성능을 평가하기 위하여 형광물질인 Rhodamine B 용액을 이용하여 혼합 전과 후의 형광 분포를 분석하였으며, 약 90%의 혼합을 얻을 수 있었다. 본 연구의 미세혼합기는 복잡한 공정을 요구하지 않고 매우 간단하게 제작되었으며, 생화학시료 분석을 위한 미세시스템에 활용될 수 있다. In this study, we developed a micromixer based on the non-equilibrium electrokinetics at the junction of a microchannel and nanochannel. Two fluid streams were mixed by an electro-osmotic flow and a vortex flow created as a result of the non-equilibrium electrokinetics at the junction of the microchannel and nanochannel. Initially, the microchannel was fabricated using Polydimethylsiloxane (PDMS) by the general soft lithography process and the nanochannel was created at a specific position on the microchannel by applying a high voltage. To evaluate the mixing performance of the micromixer, fluorescent distribution was analyzed by using the fluorescent dye, Rhodamine B. About 90% mixing was achieved with this novel micromixer, and this micromixer can be used in microsystems for biochemical sample analysis.
단순공정을 통해 제작된 나노채널의 불균형 동전기성을 이용한 미세혼합기 연구
유사무엘(Samuel Yu),윤헌준(Heon Jun Yoon),이상영(Sang Young Lee),김선민(Sun Min Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Our mixer is based on a concept of non-equilibrium electrokinetics of micro/nanochannel at a junction of a micro and nanochannel. The nanochannel was created using the breakdown method within very short time. Spontaneous discharge leaves behind branched nanochannel, called nanofissure which was formed by electrical breakdown. Electrical shock (1000㎳, 1400V) was applied to create nanochannels by destructing the PDMS membrane in the between two microchannels. After fabricating nanochannels, Voltage (250V) was applied near the entrance of the nanochannel. A strong vortex was found to be generated near the entrance of the nanochannel due to electrical imbalance and which causes the fluids to mix. The impedance of the nanochannel is larger than the microchannel. This device is a efficient to mix the fluid and simply fabricated.
플라즈마 표면 처리 된 PDMS 막의 인장으로 생성된 미세패턴을 이용한 세포 접촉 유도 연구
유사무엘(Samuel Yu),최성균(Seongkyun Choi),요시츠미 마스모토(Yoshizumi Masumoto),타이치 히로세(Taichi Hirose),마사히토 반(Masahito Ban),김선민(Sun Min Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
Recently, contact guidance of cells using micro/nanopatterns has been widely investigated for mimicking in vivo environments. In this study, we used different types of micro-patterned surface as contact guidance for enhancing cell adhesion and growth. Micro/nanopatterns were created by stretching PDMS membrane exposed to plasma. Three different types of cells were cultured for 3 days on patterned PDMS surface to analyze cell growth and proliferation with phase contrast microscope. Also, the distribution of angle between patterns axis and cells axis were measured. Cultured cells on patterned PDMS surface were elongated along contact guidance and morphology of them was changed according to size of pattern and type of cell. This study will be helpful for the study on cell-surface interactions.
High-resolution three-photon biomedical imaging using doped ZnS nanocrystals
Yu, Jung Ho,Kwon, Seung-Hae,Petrá,š,ek, Zdeně,k,Park, Ok Kyu,Jun, Samuel Woojoo,Shin, Kwangsoo,Choi, Moonkee,Park, Yong Il,Park, Kyeongsoon,Na, Hyon Bin,Lee, Nohyun,Lee, Dong Won,Kim, Nature Publishing Group 2013 NATURE MATERIALS Vol.12 No.4
Three-photon excitation is a process that occurs when three photons are simultaneously absorbed within a luminophore for photo-excitation through virtual states. Although the imaging application of this process was proposed decades ago, three-photon biomedical imaging has not been realized yet owing to its intrinsic low quantum efficiency. We herein report on high-resolution in vitro and in vivo imaging by combining three-photon excitation of ZnS nanocrystals and visible emission from Mn<SUP>2+</SUP> dopants. The large three-photon cross-section of the nanocrystals enabled targeted cellular imaging under high spatial resolution, approaching the theoretical limit of three-photon excitation. Owing to the enhanced Stokes shift achieved through nanocrystal doping, the three-photon process was successfully applied to high-resolution in vivo tumour-targeted imaging. Furthermore, the biocompatibility of ZnS nanocrystals offers great potential for clinical applications of three-photon imaging.
Seismic Performance of Concrete Columns with Innovative Seven- and Eleven-Spiral Reinforcement
Ou, Yu-Chen,Ngo, Si-Huy,Roh, Hwasung,Yin, Samuel Y.,Wang, Jui-Chen,Wang, Ping-Hsiung American Concrete Institute 2015 ACI structural journal Vol.112 No.5
<p>This research proposes innovative seven- and 11-spiral transverse reinforcement to replace two- and six-spiral reinforcement, respectively, to decrease spiral size to address the issue of spiral fabrication in large columns. Moreover, this research proposes using large reinforcing bars or H-shaped steel as longitudinal reinforcement to reduce the potential of reinforcing bar cage failure. The objectives of this research were to investigate the seismic performance of seven- and 11-spiral columns and the effect of using large reinforcing bars and H-shape steel as longitudinal reinforcement. Cyclic tests of columns showed that seven- and 11-spiral columns, even with less amounts of transverse reinforcement, exhibited higher ductility capacities than tied columns. The use of H-shaped steel as longitudinal reinforcement increased ductility and energy dissipation of the column. Among ACI 318, Caltrans BDS, and Caltrans SDC methods to estimate probable moment strength, only the Caltrans SDC method produced conservative results for all columns examined.</p>
Chuah Tyng Yu,Lim Chun Yee,Tan Rui Zhen,Pratumvinit Busadee,Loh Tze Ping,Vasikaran Samuel,Markus Corey,APFCB Harmonization of Reference Intervals Working Group 대한진단검사의학회 2023 Annals of Laboratory Medicine Vol.43 No.5
Functional reference limits describe key changes in the physiological relationship between a pair of physiologically related components. Statistically, this can be represented by a significant change in the curvature of a mathematical function or curve (e.g., an observed plateau). The point at which the statistical relationship changes significantly is the point of curvature inflection and can be mathematically modeled from the relationship between the interrelated biomarkers. Conceptually, they reside between reference intervals, which describe the statistical boundaries of a single biomarker within the reference population, and clinical decision limits that are often linked to the risk of morbidity or mortality and set as thresholds. Functional reference limits provide important physiological and pathophysiological insights that can aid laboratory result interpretation. Laboratory professionals are in a unique position to harness data from laboratory information systems to derive clinically relevant values. Increasing research on and reporting of functional reference limits in the literature will enhance their contribution to laboratory medicine and widen the evidence base used in clinical decision limits, which are currently almost exclusively contributed to by clinical trials. Their inclusion in laboratory reports will enhance the intellectual value of laboratory professionals in clinical care beyond the statistical boundaries of a healthy reference population and pave the way to them being considered in shaping clinical decision limits. This review provides an overview of the concepts related to functional reference limits, clinical examples of their use, and the impetus to include them in laboratory reports.
Lee, Ki-Jeong,Kim, Yu-Jeong,Koomson, Samuel,Lee, Choong-Gon The Korean Electrochemical Society 2018 Journal of electrochemical science and technology Vol.9 No.2
This study evaluated the performance characteristics of varied electrolyte species and amounts in a molten carbonate fuel cell (MCFC). Coin-type MCFCs were used at the condition of $650^{\circ}C$ and 1 atm. In order to measure the effects of varied electrolyte species and amounts, electrolytes of $(Li+K)_2CO_3$ and $(Li+Na)_2CO_3$ were selected and the amounts of 1.5 g, 2.0 g, 3.0 g, and 4.0 g were used. Insignificant performance differences were observed in the cell using different electrolytes, but the cell performance was sensitive to the amount of the electrolyte used. The pore-filling ratio (PFR), a ratio of pore filling in the components by the liquid carbonate electrolytes, was used to determine the optimum performance range. Consequently, 77% PFR demonstrated the optimum performance for both electrolytes. Thus, the MCFC had a permissible but narrow optimum performance range. The remaining amounts of electrolyte in the cells were determined using the weight reduction ratio (WRR) method after several hours of cell operation. The WRR used the relationship between the initial loaded amount of electrolyte and weight reduction of components in 10 wt% acetic acid. The relationships were linear and identical between the two electrolyte species.