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Study of SU-8 to make a Ni master-mold: Adhesion, sidewall profile, and removal
Kim, Sung-Jin,Yang, Haesik,Kim, Kyuwon,Lim, Yong Taik,Pyo, Hyeon-Bong WILEY-VCH Verlag 2006 Electrophoresis Vol.27 No.16
<P>For disposable microfluidic devices, easy and inexpensive fabrication is essential. Consequently, replication of microfluidic devices, using injection molding or hot embossing, from a master-mold is widely used. However, the conventional master-mold fabrication technique is unsatisfactory in terms of time and costs. In this regard, direct Ni growth (electroplating) from a back plate is promising when the photoresist is well-defined. Here, we demonstrate the use of SU-8 as a photoresist to define the Ni-growth region. We accomplish this application by focusing on the adhesion, the sidewall profile, and the removal of SU-8: the adhesion is enhanced by controlling the exposure dose, the soft-baking time, and by choosing the adhesion-promoting layer; the sidewall profile is regulated by selecting the intensity of each exposed wavelength, showing an aspect ratio of up to 20.9; and, easy removal is achieved by choosing a proper photoresist-stripper. Using the master-mold fabricated by this method, we test the mechanical stability of the features according to the aspect ratio and length; in the hot embossing process, the features are stable in the aspect ratio of up to 5.8 at a length of 200 µm. In addition, the plastic devices fabricated from this method are applied to the passive stop valves, showing a capillary pressure (−0.2 to −7.2 kPa).</P>
Kim, Sung-Jin,Lim, Yong Taik,Yang, Haesik,Kim, Kyuwon,Kim, Youn Tae WILEY-VCH Verlag 2010 Electrophoresis Vol.31 No.4
<P>Biochemical solutions have a wide range of hydrophilicity (contact angle and surface tension) and viscosity. A critical challenge is that microfluidic systems typically need expensive or complex pumps to control the various parallel biochemical streams. In this study, without using any pumps, we present a simple scheme that controls the ratio of the volumetric flow rate (VFR) of the parallel streams that have highly different hydrophilicity and viscosity. We accomplish this process by using capillarity to drive and merge two streams, and by regulating relative flow resistance to control the VFR ratio. Our results will significantly simplify the control of the VFR ratio for the various biochemical solutions that are used in microfluidic applications.</P>
Nonlinear Product Codes and Their Low Complexity Iterative Decoding
Haesik Kim,Garik Markarian,Valdemar C. da Rocha, Jr 한국전자통신연구원 2010 ETRI Journal Vol.32 No.4
This paper proposes encoding and decoding for nonlinear product codes and investigates the performance of nonlinear product codes. The proposed nonlinear product codes are constructed as N-dimensional product codes where the constituent codes are nonlinear binary codes derived from the linear codes over higher order alphabets, for example, Preparata or Kerdock codes. The performance and the complexity of the proposed construction are evaluated using the well-known nonlinear Nordstrom-Robinson code, which is presented in the generalized array code format with a low complexity trellis. The proposed construction shows the additional coding gain, reduced error floor, and lower implementation complexity. The (64, 24, 12) nonlinear binary product code has an effective gain of about 2.5 dB and 1 dB gain at a BER of 10<sup>-6</sup> when compared to the (64, 15, 16) linear product code and the (64, 24, 10) linear product code, respectively. The (256, 64, 36) nonlinear binary product code composed of two Nordstrom-Robinson codes has an effective gain of about 0.7 dB at a BER of 10-5 when compared to the (256, 64, 25) linear product code composed of two (16, 8, 5) quasi-cyclic codes.
김남종 ( Namjong Kim ),박해식 ( Haesik Park ),장현상 ( Hyeonsang Jang ) 한국경제학회 2021 經濟學硏究 Vol.69 No.1
본 연구는 국내 외환당국의 시장개입이 원/달러 환율에 미치는 영향을 실증적으로 분석하였다. 이를 위해 2000년 1월~2018년 12월을 표본기간으로 하여 언론 매체의 기사와 자금중개회사의 시황자료를 통해 일별 개입자료(실개입 및 구두개입)를 구축하였다. 개입자료의 군집성 등을 고려하여 시계열분석보다는 사건연구에 의존하여 개입의 유효성을 검증하였다. 사건연구는 개입자료에서 개입 이벤트를 선정한 다음에 개입 이벤트의 성공률을 추정하고 비모수부호검정 기법을 통해 개입 성공률의 유의성을 검증하는 방식으로 진행하였다. 주요결과는 다음과 같다. 국내 외환당국의 시장개입은 원/달러 환율에 유의한 영향을 미치는 것으로 나타났다. 실개입과 구두개입의 영향력을 비교한 결과, 구두개입보다는 실개입의 영향력이 더 큰 것으로 나타났다. 또한, 일회성 개입보다는 반복적 개입이 더 유효하다는 결과를 발견하였다. We conduct an empirical analysis to examine the effectiveness of foreign exchange market interventions in Korea. Daily data of both actual and oral interventions are constructed using information extracted from media articles and market reviews of the Korean Money Brokerage Corporation during the period from January 2000 to December 2018. We employ an event study approach to take into account the clustering feature of constructed intervention data. The event study is implemented by identifying intervention events from the intervention data, estimating their success rates, and verifying statistical significance of the success rates through a nonparametric test. Our main findings are as follows. We find that interventions in the Korean foreign exchange market exert significant influence on the won/dollar exchange rate. Actual interventions are estimated to have greater influence than oral interventions. Repeated interventions are found to be more effective than one-time interventions.