• 한국식품위생안전성학회지
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• 제14권1호
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• pp.76-83
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• 1999

Solid phase microextraction (SPME) was used for the determination of 6 standard solvents (methanol, isopropanol, methyl ethyl ketone, ethyl acetate, cyclohexane, toluene) in food packaging materials. SPME method is a solvent-free sample preparation technique in which a fused silica fiber coated with polymeric organic liquid is introduced into the headspace above the sample. SPME method using fiber coated polydimethylisiloxane (PDMS) was compared with static headspace (SHS) method used as a reference. It was found that the optimal adsorption condition using PDMS-SPME method was 2$0^{\circ}C$ for 15 minutes for the standard solvents. Detection limits, linearity, reproducibility and recovery of both SHS and PDMS-SPME methods have been determined using 6 standard solvents. Both methods were characterized by high reproducibility and good linearity. Using SHS methods, the mean recovery of the 6 standard solvents was ranged from 75.5% to 105.8% with a mean relative standard deviation (RSD) of 0.3% to 4.8%. With PDMS-SPME method, the mean recovery of the 6 standard solvents was ranged from 86.7% to 108.3% with a mean RSD of 0.4% to 2.5%. The detection limits of both methods were the same for toluene, cyclohexane and methyl ethyl ketone; those of PDMS-SPME method were higher than those of SHS method for methanol, isopropanol and ethyl acetate. PDMS-SPME fiber shoed excellent adsorption for non-polar solvents such as toluene, while it showed relatively low adsorption for polar solvents such as methanol.

• 한국통신학회논문지
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• 제19권5호
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• pp.787-795
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• 1994

본 논문에서는 랜덤한 NRZ 신호에 동기된 클럭을 추출하는 비트 동기 알고리즘을 제안하고 회로 설계 및 성능을 분석하였다. 설계된 동기 회로는 데이터 천이 검출기, Mod 64 계수기, 위상비교 및 제어기, 64분주기로 구성되었으며, 데이터 처리 속도가 16Kbps로서 마스터 클럭은 4.096MHz, 그리고 위상 보정은 매 비트마다 데이터 신호 주기의 1/64만큼 이루어진다. 입력신호에 대한 위상 지터의 최대 허용치는 23.8%이고, 복원된 클럭의 편차가 1.6%임을 실험을 통해 측정하였다. 동기 회로는 완전 디지틀 회로로서 하나의 반도체 칩으로 실현이 용이할 뿐 아니라 저속의 디지틀 이동통신에 효과적이다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.241-246
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• 2007

The present paper dealt with an experimental study of boiling heat transfer characteristics of $CO_2$. Heat transfer coefficients of the refrigerant flow inside horizontal smooth microchannel were obtained with inner tube diameter of 0.3mm and length of 300mm. The direct electric heating method was applied for supplying the heat uniformly to the refrigerant. The experiments were conducted with $CO_2$ purity of 99.99%, at saturation temperature of $10^{\circ}C$, mass flux ranges of $300{\sim}900\;kg/m^2s$, and heat flux ranges of $15{\sim}45\;kW/m^2$. While heat transfer coefficient increased with the increase of heat flux in the low quality region, the heat transfer coefficient decreased with the increase of quality in the high quality region. The heat transfer coefficients were compared with seven existing correlations with the Gungor-Winterton's(1986) correlation gave the best prediction. A new corelation to predict the two-phase flow heat transfer coefficient was developed based on the Chen(1966) correlation. The new correlation predicted the experimental data well with a mean deviation of 9.69% and average deviation of -3.03%.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1626-1634
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• 2015

LCL filters are widely used in three-phase PWM converter for its advantages of small volume, low cost and inhibition of high frequency current harmonic. However, it is difficult to optimize its design because its parameters are mutually influenced while the value of each parameter for LCL filter has impacts on the converter's cost and size. In this paper, the target of optimization is to minimize the parameter values of LCL filter, and an optimization method for parameters of LCL filter of three-phase PWM converter based on least square method is proposed. With this method, a quantitative calculation of the harmonic component of the converter’s side phase voltage is performed first, and then the quantitative relationship between phase voltage harmonics and grid phase current harmonics is analyzed. After that, the attenuation requirement of each harmonic is obtained by taking into account the requirements for each harmonic component of grid current. Then according to the optimization objective, the objective function with minimum harmonic attenuation deviation is established, and least squares method is adopted for three-dimensional global searching of parameters for LCL filter. Thus, the designed harmonic attenuation curve approximates the minimum attenuation requirements, and the optimized LCL filter parameters are obtained. Finally, the effectiveness of the method is verified by the experiments.

• Korean Chemical Engineering Research
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• 제43권3호
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• pp.387-392
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• 2005

Dimethyl carbonate(DMC)는 낮은 독성과 빠른 생분해성으로 인해 MTBE(methyl tert-butyl ether)를 대체할 수 있는 무연가솔린의 첨가제로 주목받는 물질로, 주로 methanol의 carbonylation에 의해 합성되고, 원가절감을 위해 methanol을 출발물질로 한 새로운 DMC 제조공정의 개발이 진행 중에 있다. 이에 필요한 다양한 조건하의 DMC 관련 혼합계의 상평형 자료 및 물성은 Dortmund Data Bank(DDB)검색 결과, 매우 부족하며 무한희석 활동도계수에 대한 자료는 전무한 것으로 나타났다. 이 글에서는 methanol+DMC계의 333.15 K에서의 이성분계 등온 기-액 평형과, 혼합물성으로써 methanol+DMC계의 과잉부피 및 점도편차를 298.15 K에서 측정하였다. 또한, 무한희석상태에서 DMC 용매에서의 methanol의 무한희석 활동도계수를 303.15, 313.15, 323.15 K에서 각각 측정하였으며, 측정값은 modified UNIFAC(Dortmund)식에 의한 계산 값과도 비교하였다.

• 전자공학회논문지
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• 제53권12호
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• pp.15-19
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• 2016

매우 큰 사이즈를 가진 multi-finger RF MOSFET의 $S_{11}$-parameter에서 스미스차트의 저항 circle 라인을 벗어나는 kink 현상의 게이트 바이어스 종속 특성이 관찰되었다. 이러한 바이어스 종속성은 $S_{11}$-parameter의 크기와 위상, 입력저항, 입력 커패시턴스의 주파수 응답곡선을 측정하여 최초로 분석되었다. 그 결과 입력 커패시턴스의 크기와 입력저항의 dominant pole과 zero 주파수에 의해 $V_{gs}$ 종속 kink 현상이 크게 변하는 것을 알 수 있다. $V_{gs}=0V$일 때 매우 적은 $S_{11}$-parameter 위상차와 입력저항의 높은 pole 주파수에 의해 고주파영역에서 kink 현상이 나타난다. 하지만 $V_{gs}$가 높아지면 $S_{11}$-parameter 위상차가 크게 증가하고 pole 주파수가 낮아져 저주파영역에서 kink 현상이 발생하게 된다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1519-1526
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• 2023

For the first time Aluminium-BariumeZinc oxide nanocomposite (ZABONC) was synthesized by solution combustion method where calcination was carried out at low temperatures (600℃) to study the electromagnetic (EM) (X/γ) radiation shielding properties. Further for characterization purpose standard techniques like PXRD, SEM, UV-VISIBLE, FTIR were used to find phase purity, functional groups, surface morphology, and to do structural analysis and energy band gap determination. The PXRD pattern shows (hkl) planes corresponding to spinel cubic phase of ZnAl₂O4, cubic Ba(NO₃)₂, α and γ phase of Al₂O₃ which clearly confirms the formation of complex nano composite. From SEM histogram mean size of nano particles was calculated and is in the order of 17 nm. Wood and Tauc's relation direct energy band gap calculation gives energy gap of 2.9 eV. In addition, EM (X/γ) shielding properties were measured and compared with the theoretical ones using standard procedures (NaI (Tl) detector and multi channel analyzer MCA). For energy above 356 keV the measured shielding parameters agree well with the theory, while below this value slight deviation is observed, due to the influence of atomic/crystallite size of the ZABONC. Hence synthesized ZABONC can be used as a shielding material in EM (X/γ) radiation shielding.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2813-2818
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• 2010

A novel method was developed for the speciation of chromium in natural water samples based on homogeneous liquid-liquid extraction and determination by flame atomic absorption spectrometry (FAAS). In this method, Cr(III) reacts with a new Schiff's base ligand to form the hydrophobic complex, which is subsequently entrapped in the sediment phase, whereas Cr(VI) remained in aqueous phase. The Cr(VI) assay is based on its reduction to Cr(III) by the addition of sodium sulfite to the sample solution. Thus, separation of Cr(III) and Cr(VI) could be realized. Homogeneous liquid-liquid extraction based on the pH-independent phase-separation process was investigated using a ternary solvent system (water-tetrabutylammonium ion ($TBA^+$)-chloroform) for the preconcentration of chromium. The phase separation phenomenon occurred by an ion-pair formation of TBA and perchlorate ion. Then sedimented phase was separated using a $100\;{\mu}L$ micro-syringe and diluted to 1.0 mL with ethanol. The sample was introduced into the flame by conventional aspiration. After the optimization of complexation and extraction conditions such as pH = 9.5, [ligand] = $1.0{\times}10^{-4}\;M$, [$TBA^+$] = $2.0{\times}10^{-2}\;M$, [$CHCl_3$] = $100.0\;{\mu}L$ and [$ClO_4$] = $2.0{\times}10{-2}\;M$, a preconcentration factor (Va/Vs) of 100 was obtained for only 10 mL of the sample. The relative standard deviation was 2.8% (n = 10). The limit of detection was sufficiently low and lie at ppb level. The proposed method was applied for the extraction and determination of chromium in natural water samples with satisfactory results.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1209-1218
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• 2001

The present paper proposes a new correlation for the flow boiling heat transfer coefficients in the low flow rate condition (Re(sub)LF$\leq$200) within horizontal rectangular channels with small gaps (heights). The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated with the heat flux range of 3-15kW/㎡. The quality range covers from 0.19 to 0.76 and the flow pattern is considered to be annular. The measured heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely with the smaller gap size, the heat transfer is primarily controlled by the liquid film thickness. The proposed F factor for the heat transfer coefficient in the range of Re(sub)LF$\leq$200 well represents the experimental data within the deviation of $\pm$20%. The Kandlikars flow boiling correlation covers the higher flow-rate range(Re(sub)LF>200) within the deviation of $\pm$20%.

• Journal of Positioning, Navigation, and Timing
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• 제6권4호
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• pp.149-157
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• 2017

In this study, a system that precisely determines the heave of ship hull was designed using time-differenced GNSS carrier phase measurement, and the performance was examined. First, a technique that calculates precise position relative to the original position based on TDCP measurement for point positioning using only one receiver was implemented. Second, to eliminate the long-cycle drift error occurring due to the measurement error that has not been completely removed by time-differencing, an easily implementable high-pass filter was designed, and the optimum coefficient was determined through an experiment. In a static experiment based on the precise heave measurement system implemented using low-cost commercial GNSS receiver and PC, the heave could be measured with a precision of 2 cm standard deviation. In addition, in a dynamic experiment where it moved up and down with an amplitude of 48 cm and a cycle of 20 seconds, precise heave without drift error could be determined. The system proposed in this study can be easily used for many applications, such as the altitude correction of fish detection radar.