• Journal of Photoscience
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• 제9권1호
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• pp.23-28
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• 2002

In order to obtain thermal-stable, low birefringent, and low optical loss waveguiding materials, we synthesized several fluorinated poly (maleimide-co-glycidylmethacrylate)s using a pentafluorophenylmaleimide (PEM) and two kinds of methacrylate derivatives as comonomers and glycidylmethacrylate as a crosslinker. One comonomer is a linear fluorinated methacrylate (HFBM) and another is a bulky norbornane-derived methacrylate (NMMA). These copolymers could be self-crosslinked by heating due to epoxy groups of glycidylmethacrylates. As a maleimide contents increased to 50 mol%, these copolymers showed high decomposition temperatures of above 300$^{\circ}C$. The refractive index could be precisely controlled by the variation of PFM/HFBA or PFM/NMMA feed ratio in the range of 1.410∼1.508 at 643 nm. The copolymers had very low birefringence in the range of 1∼5${\times}$10$\^$-4/.

• 전기전자학회논문지
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• 제19권4호
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• pp.465-471
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• 2015

An LC-tuned sinusoidal voltage-controlled oscillator (VCO) using temperature-stable linear operational transconductance amplifiers (OTAs) is presented. Its architecture is based on Hartley oscillator configuration, where the inductor is active one realized with two OTAs and a grounded capacitor. Two diode limiters are used for limiting amplitude. A prototype oscillator built with discrete components exhibits less than 3.1% nonlinearity in its current-to-frequency transfer characteristic from 1.99 MHz to 39.14 MHz and $220ppm/^{\circ}C$ frequency stability to the temperature drift over 0 to $75^{\circ}C$. The total harmonic distortion (THD) is as low as 4.4 % for a specified frequency-tuning range. The simulated phase noise of the VCO is about -108.9 dBc/Hz at 1 MHz offset frequency in frequency range of 0.4 - 46.97 MHz and property of phase noise of VCO is better than colpitts-VCO.

• 센서학회지
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• 제17권5호
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• pp.329-337
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• 2008

Simple, small and portable oxygen sensors were fabricated by tape casting technique. Yttria stabilized zirconia containing cordierite ceramics (YSZC) were used as a porous diffused layer of oxygen in pumping cell. Yttria stabilized zirconia (YSZ) solid electrolyte, YSZC porous diffusion layer and heater-patterned ceramic sheets were prepared by co- firing method. Limit current characteristics and the linear relationship of current to oxygen concentration were observed. Viscosity variation of the slurries both YSZ and YSZC showed a similar behavior, but micro pores in the fired sheet were increased with increasing of the cordierite amount. Molecular diffusion was dominated due to the formation of large pores in porous diffusion layer. The plateau range of limit current in porous-type oxygen sensor was narrow than the one of aperture-type oxygen sensor. However limit current curve was appeared in porous-type oxygen sensor even at the lower applied voltage. The plateau range of limit-current was widen as increasing the thickness of porous diffusion layer of the YSZ containing cordierite. Measuring temperature of $600{\sim}650^{\circ}C$ was recommended for limit-current oxygen sensor. Porous diffusion layer-type oxygen sensor showed faster response than the aperture-type one and was stable up to 30 days running without any crack at interface between the layers.

• Journal of Korean Neurosurgical Society
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• 제61권1호
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• pp.60-65
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• 2018

Objective : Choroidal metastases (CMs) are the most common intraocular tumor. Management is mainly radiation therapy with goals of pain control and visual improvement. However, many radiation-related complications are reported. Since gamma knife radiosurgery (GKS) for CM was first reported in 1995, few cases have been reported. We report 7 cases of CMs treated with GKS. Methods : From April 2011 to November 2014, 7 patients with CM underwent GKS. Their median age at treatment was 64 years (range, 51-71 years). Four males and three females were treated. Lung cancer was the most common primary pathology, followed by renal cell carcinoma and stomach cancer. Four patients had multiple cerebral lesions and were treated simultaneously for choroidal lesions. The median marginal dose of 20 Gy (range, 15-25 Gy) was administered at the 50% isodose line. Results : Median follow-up period after GKS was 8 months (range, 2-38.3 months). Four patients expired due to underlying malignancy progression. Except for two patients who were not followed with magnetic resonance image after GKS, all patients showed size reduction in the treated lesions, but a new choroidal lesion appeared in one patient and one recurred. Six of seven patients reported subjectively improved visual symptoms. Visual acuity improved in 2 patients, and 2 were stable upon objective examination. One patient showed no improvement in visual acuity, but ocular pain was relieved; another patient showed improved vision and tumor remission, but visual deterioration recurred. Conclusion : GKS was shown to be safe and effective and should be considered for CM treatment.

• Nuclear Engineering and Technology
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• 제33권4호
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• pp.409-422
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• 2001

The dynamic character of a system of the governing differential equations for the one- dimensional two-fluid model, where the momentum flux parameters are employed to consider the velocity and void fraction distribution in a flow channel, is investigated. In response to a perturbation in the form of a＇traveling wave, a linear stability analysis is peformed for the governing differential equations. The expression for the growth factor as a function of wave number and various flow parameters is analytically derived. It provides the necessary and sufficient conditions for the stability of the one-dimensional two-fluid model in terms of momentum flux parameters. It is demonstrated that the one-dimensional two-fluid model employing the physical momentum flux parameters for the whole range of dispersed flow regime, which are determined from the simplified velocity and void fraction profiles constructed from the available experimental data and $C_{o}$ correlation, is stable to the linear perturbations in all wave-lengths. As the basic form of the governing differential equations for the conventional one-dimensional two-fluid model is mathematically ill posed, it is suggested that the velocity and void distributions should be properly accounted for in the one-dimensional two-fluid model by use of momentum flux parameters.s.

• 전자공학회논문지A
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• 제28A권12호
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• pp.46-52
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• 1991

A new signal process circuit using two ISFETs as the input devices of the MOS differential amplifier stage for an ISFET biosensor has been developed. One chip integration of the newly developed signal process circuit, ISFETs and a Pt quasi-reference electrode has been carried out according to modified LOCOS p-well CMOS process. The fabricated chip showed gains of 0.8 and 1.6, good liniarity in the input-output relationship and very small power dissipation, 4mW. The chip was applied to realize a urea sensor by forming an immobilized urease membrane, using lift-off technique. on the gate of an ISFET. The urea sensor chip showed stable responses in a wide range of urea concentrations.

• 해양환경안전학회지
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• 제24권3호
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• pp.325-331
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• 2018

This paper deals with the dynamical analysis of a vessel that leads to capsize in regular beam seas. The complete investigation of nonlinear behaviors includes sub-harmonic motion, bifurcation, and chaos under variations of control parameters. The vessel rolling motions can exhibit various undesirable nonlinear phenomena. We have employed a linear-plus-cubic type damping term (LPCD) in a nonlinear rolling equation. Using the fourth order Runge-Kutta algorithm with the phase portraits, various dynamical behaviors (limit cycles, bifurcations, and chaos) are presented in beam seas. On increasing the value of control parameter ${\Omega}$, chaotic behavior interspersed with intermittent periodic windows are clearly observed in the numerical simulations. The chaotic region is widely spread according to system parameter ${\Omega}$ in the range of 0.1 to 0.9. When the value of the control parameter is increased beyond the chaotic region, periodic solutions are dominant in the range of frequency ratio ${\Omega}=1.01{\sim}1.6$. In addition, one more important feature is that different types of stable harmonic motions such as periodicity of 2T, 3T, 4T and 5T exist in the range of ${\Omega}=0.34{\sim}0.83$.

• Korean Chemical Engineering Research
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• 제40권6호
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• pp.769-777
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• 2002

Nonionic surfactant/water/탄화수소 오일/alcohol의 4성분계 시스템에서 12종의 조성물을 제조하여 물성 평가를 수행한 결과, 30.5-31.1 dyne/cm의 낮은 표면장력의 값과, 1.6-7.2 c.p.의 낮은 점도의 물성을 보여 산업용 세정제로서의 기본 물성을 보여주었다. 이들 조성물들이 안정한 단일상으로 존재하는 온도의 범위는 alcohol/surfactant(A/S)비의 증가에 따라 감소되는 경향을 보이고 있으나, 전체적으로는 계면활성제의 hydrophilic lipophilic balance(HLB) 값에 크게 영향을 받고 있으며, HLB 값이 높을수록 안정하게 존재하는 온도 영역이 증가되는 경향을 보여주고 있다. 그리고 각각의 조성물에 물의 함량을 증가 시켜 안정한 단일상이 유지되는 물의 최대 함유량을 측정한 결과 HLB 값이 낮은 계면활성제를 사용하였을 경우 HLB 값이 6.4인 비이온 계면활성제를 사용할 경우 22.1%까지도 물을 함유할 수 있었고, 물의 양이 증가됨에 따라서 단일상으로 존재하는 온도영역은 좁아졌다. 오염원으로 플럭스 제조에 사용되는 abietic acid에 대한 세정 효율을 UV/Visable Spectrophotometer와 FT-IR Spectrometer와 같은 분석기기를 이용하여 검토하여 본 결과, 비이온 계면활성제의 HLB 값이 낮을수록 높은 세정 효율을 보여주어, W/O microemulsion의 경우 비이온 계면활성제에 따른 세정력의 변화가 매우 큼을 확인 할 수 있었다. 그러나 A/S의 비가 증가에 따른 세정효율의 차이는 별다른 경향을 보이지 않았다. 또한 산업세정에 있어서 중요한 세정 요소로 작용하는 변수인 온도 변화와 초음파 주파수의 변화에 따른 세정효율을 측정한 결과, 온도가 높을수록 그리고 초음파의 주파수가 낮을수록 높은 세정력을 보여주었다. 세정 공정 중 린스조에서의 유분 오염물이 함유된 린스액의 유수분리 효율을 측정한 결과, HLB 값이 6.4인 비이온 계면활성제를 사용한 시스템의 경우 $25^{\circ}C$ 이상에서 85% 이상의 높은 제거 효율을 보여, 효율적인 세정 및 관리가 가능한 것으로 판단되었다.

• 한국식품영양과학회지
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• 제24권4호
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• pp.636-641
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• 1995

Proteolytic activities were compared using three species involving in squid jeotkal fermentation and showing positive reaction upon casein test : Pseudomonas D2, Flavovacterium odoratum and Acinetobacter calcoaceticus. Pseudomonas D2 produced highest activity of protease at 72h when incubated in our own modified medium(polypeptone, 0.5% ; tryptone, 0.5% ; NaCl, 3% ; pH, 7.5). Thus, this specie was selected for the further study. The growth pattern was coincided with the production of protease. Thus purification of protease was proceeded by ethanol precipitation, sephadex G-100 gel filtration, and DEAE sepharose ion exchange chromatography. The purified protease showed highest activity at pH 7.0 and 5$0^{\circ}C$. The enzyme was very stable over the wide ragnes of the temperature ; even with one hour heat treatment at 7$0^{\circ}C$, the enzyme showed substantial amount of the activity toward casein. In addition, the enzyme was stable over the wide range of pH. Molecular weight of the protease was determined to be 17.4 kD by SDS-PAGE.

• 한국정보처리학회논문지
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• 제6권6호
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• pp.1571-1580
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• 1999

데이터 마이닝 또는 기계학습을 위한 무감독 학습 알고리즘인 개념적 클러스터링을 이용하여 계층적 구조를 유도해낼 때 자료를 처리하는 순서에 따라 서로 다른 결과에 도달하는 양상을 보인다. 이 순서 바이어스 문제를 해결하는 방안으로 먼저 주어진 자료 세트에 분류를 시행하여 초기 분류를 형성한다. 이 분류를 통해 최종 분류의 가능한 클래스 수를 예측하고 이 정보에 기반하여 자료 분석과 중심 정렬을 통해 자료 처리 순서를 새로이 결정한다. 재배열된 자료 세트에 ITERATE 분류 과정을 적용해 새로운 분류를 생성한다. 본 논문에서는 이 과정을 반복하여 안정적이고 최적의 분류 점수를 갖도록 하는 알고리즘 REIT를 제안하였다. 이 알고리즘을 여러 자료 세트에 적용하고 순서 바이어스의 영향을 최소화하는지 여부를 실험을 통해 비교 분석하였다.