• Journal of Korea Water Resources Association
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• v.39 no.4 s.165
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• pp.299-311
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• 2006

In this paper it is outlined the methodology of estimating the parameters of water balance analysis method for calculating recharge, using ground water level rises in monitoring well when values of specific yield of aquifer are not available. This methodology is applied for two monitoring wells of the case study area in northern area of the Jeiu Island. A water balance of soil layer of plant rooting zone is computed on a daily basis in the following manner. Diect runoff is estimated by using SCS method. Potential evapotranspiration calculated with Penman-Monteith equation is multiplied by crop coefficients($K_c$) and water stress coefficient to compute actual evapotranspiration(AET). Daily runoff and AET is subtracted from the rainfall plus the soil water storage of the previous day. Soil water remaining above soil water retention capacity(SWRC) is assumed to be recharge. Parameters such as the SCS curve number, SWRC and Kc are estimated from a linear relationship between water level rise and recharge for rainfall events. The upper threshold value of specific yield($n_m$) at the monitoring well location is derived from the relationship between rainfall and the resulting water level rise. The specific yield($n_c$) and the coefficient of determination ($R^2$) are calculated from a linear relationship between observed water level rise and calculated recharge for the different simulations. A set of parameter values with maximum value of $R^2$ is selected among parameter values with calculated specific yield($n_c$) less than the upper threshold value of specific yield($n_m$). Results applied for two monitoring wells show that the 81% of variance of the observed water level rises are explained by calculated recharge with the estimated parameters. It is shown that the data of groundwater level is useful in estimating the parameter of water balance analysis method for calculating recharge.

• Journal of the Korean GEO-environmental Society
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• v.8 no.4
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• pp.19-25
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• 2007

Process analysis with ASM3 (Activated Sludge Model3) was performed to offer basic data for the optimization of aerated biofilter (ABF) process design and operation. This study was focused on the simulation of the nitrification reaction in ABF which was a part of the advanced nutrient treatment process using bio-adsorption. The ABF process has been developed for the removal of suspended solids and nitrification reaction in sewage. A GPS-X (General Purpose Simualtor-X) was used for the sensitivity analysis and operation assessment. Sensitivity of ASM3 parameters on ABF was analysed and 4 major parameters ($Y_A$, $k_{sto}$, ${\mu}_A$, $K_{A,HN}$) were determined by dynamic simulation using 70 days data from pilot plant operation. The optimized values were 0.14 for $Y_A$, 3.5/d for $k_{sto}$, 2.7/d for ${\mu}_A$ and 1.1 mg/L for $K_{A,HN}$, respectively. Simulation with optimized parameter values were conducted and TN, $NH_4{^+}-N$ and $NO_3{^-}-N$ concentrations were estimated and compared with measured data at the range of 10 min to 4 hrs of hydraulic retention time (HRT). The simulated results showed that optimized parameter values could represent the characteristics of ABF process. Especially, the ABF showed relatively high nitrification rate (60%) under very short HRT of 10 min. As a consequence, the ABF was thought to be successfully used in the site which having high variation of influent loading rate.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.180-180
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• 2015

Solution processed Resistive random access memory (ReRAM)은 간단한 공정 과정, 고집적도, 저렴한 가격, 대면적화 플라즈마 데미지 최소화 등의 장점으로 차세대 비휘발성 메모리로 써 많은 관심을 받고 있으며, 주로 high-k 물질인 HfOx, TiOx, ZnO 가 이용 된다. IGZO와 ZTO와 같은 산화물 반도체는 높은 이동도, 대면적화, 넓은 밴드갭으로 인하여 투명한 장점으로 LCDs (Liquid crystal displays)에 이용 가능하며, 최근에는 IGZO와 ZTO에서 Resistive Switching (RS) 특성을 확인한 논문이 보고되면서 IGZO와 ZTO를 ReRAM의 switching medium와 TFT의 active material로써 동시에 활용하는 것에 많은 관심을 받고 있다. 이와 같은 산화물 반도체는 flat panel display 회로에 TFT와 ReRAM의 active layer로써 집적가능 하며 systems-on-panels (SOP)에 적용 가능하다. 하지만 IGZO 보다는 ZTO가 In과 Ga을 포함하지 않기 때문에 저렴하다. 그러므로 IGZO를 대신하는 물질로 ZTO가 각광 받고 있다. 본 실험에서는 ZTO film에 Al을 doping하여 메모리 특성을 평가하였다. 실험 방법으로는 p-type Si에 습식산화를 통하여 SiO2를 300 nm 성장시킨 기판을 사용하였다. 그리고 Electron beam evaporator를 이용하여 Ti를 10 nm, Pt를 100 nm 증착 한다. 용액은 Zn와 Tin의 비율을 1:1로 고정한 후 Al의 비율을 0, 0.1, 0.2의 비율로 용액을 각각 제작하였다. 이 용액을 이용하여 Pt 위에 spin coating방법을 이용하여 1000 rpm 10초, 6000 rpm 30초의 조건으로 AZTO (Al-ZnO-Tin-Oxide) 박막을 증착한 뒤, solvent 및 불순물 제거를 위하여 $250^{\circ}C$의 온도로 30분 동안 열처리를 진행하였다. 이후 Electron beam evaporator를 이용하여 top electrode인 Ti를 100 nm 증착하였다. 제작된 메모리의 전기적 특성은 HP 4156B semiconductor parameter analyzer를 이용하여 측정하였다. 측정 결과, AZTO (0:1:1, 0.1:1:1, 0.2:1:1)를 이용하여 제작한 ReRAM에서 RS특성을 얻었으며 104 s이상의 신뢰성 있는 data retention특성을 확인하였다. 그리고 Al의 비율이 증가할수록 on/off ratio가 증가하고 endurance 특성이 향상되는 것을 확인하였다. 결론적으로 Al을 doping함으로써 ZTO film의 메모리 특성을 향상 시켰으며 AZTO film을 메모리와 트랜지스터의 active layer로써 활용 가능할 것으로 기대된다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.49 no.4
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• pp.368-376
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• 2013

Fishing experiments were carried out in the adjacent sea of Yeongil Bay, the eastern cost of Korea from 2003 to 2004 using the dome-shaped pots with different five mesh sizes (17.1, 24.8, 35.3, 39.8, and 48.3mm) in order to determine the size selectivity of pots for the whelk, Buccinum opisthoplectum. The catch species were composed of Buccinum opisthoplectum (45.4%), Buccinum striatissimum (30.1%), Pandalopsis japonica (9.3%), Chionoecetes opilio (8.9%), and so on. The shell height (l) of Buccinum opisthoplectum caught in the experimental fishing pots was measured. The SELECT (Share Each Length's Catch Total) analysis method was applied with fishing data to obtain master selection curve. The model with the estimated split parameter was found to fit the catch data best. The master selection curve was estimated to be s (R)〓exp (7.833R-10.871)/[1 + exp (7.833R-10.871], where R is the ratio of shell height to mesh size. The relative shell length for 50% retention was 1.388, and the selection range was 0.281. It means that the pots of larger mesh size allow more whelks of small size to escape.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.1
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• pp.1-7
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• 2000

The SNOSFET memory devices with ultrathin ONO(tunnel oxide-nitride-blocking oxide) gate dielectric were fabricated using n-well CMOS process and investigated its characteristics. The thicknesses of tunnel oxide, nitride and blocking oxide were $23{\AA},\; 53{\AA}\; and\; 33{\AA}$, respectively. Auger analysis shows that the ONO layer is made up of $SiO_2(upper layer of blocking oxide)/O-rich\; SiO_x\N\_y$. It clearly shows that the converting layer with $SiO_x\N\_y(lower layer of blocking oxide)/N-rich SiO_x\N\_y(nitride)/O-rich SiO_x\N\_y(tunnel oxide)$. It clearly shows that the converting layer with $SiO_x\N\_y$ phase exists near the interface between the blocking oxide and nitride. The programming condition of +8 V, 20 ms, -8 V, 50 ms is determined and data retention over 10 years is obtained. Under the condition of 8 V programming, it was confirmed that the modified Fowler-Nordheim tunneling id dominant charge transport mechanism. The programmed threshold voltage is distributed less than 0.1 V so that the reading error of memory stated can be minimized. An $8\times8$ NAND type flash EEPROM with SONOSFET memory cell was designed and simulated with the extracted SPICE parameters. The sufficient read cell current was obtained and the upper limit of $V_{TH}$ for write state was over 2V.

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.21-26
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• 2008

We fabricated nano-particles of ZnO, $In_2O_3$ and $SnO_2$ by using the chemical reaction between metal thin films and polyamic acid. The average size and density of these ZnO, $In_2O_3$ and $SnO_2$ nano-particles was approximately 10, 7, and 15 nm, and $2{\times}10^{11},\;6{\times}10^{11},\;2.4{\times}10^{11}cm^{-2}$, respectively. Then, we fabricated nano-floating gate memory (NFGM) devices with ZnO and $In_2O_3$ nano-particles embedded in the devices' polyimide dielectrics and silicon dioxide layers as control and tunnel oxides, respectively. We measured the current-voltage characteristics, endurance properties and retention times of the memory devices using a semiconductor parameter analyzer. In the $In_2O_3$ NFGM, the threshold voltage shift (${\Delta}V_T$) was approximately 5 V at the initial state of programming and erasing operations. However, the memory window rapidly decreased after 1000 s from 5 to 1.5 V. The ${\Delta}V_T$ of the NFGM containing ZnO was approximately 2 V at the initial state, but the memory window decreased after 1000 s from 2 to 0.4 V. These results mean that metal-oxide nano-particles have feasibility to apply NFGM devices.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.201-210
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• 1990

The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.4
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• pp.267-273
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• 2000

The tooth selectivity of the dredge for catching venus clam (Gomphina melanaegis) was described in which the teeth penetrated the bottom and lifted the shell into the bag. Some factors affecting the selection action of the teeth of the dredge were analyzed related to shell length and shell height. The retention probability of venus clam not sifting through the gaps between the teeth was calculated for various shell lengths and was fitted to two parameter logistic selection curve. The formula obtained is as follows: $P= \frac{1}{1+exp[8.24](\frac{d}{L_1}-0.649)}$, where d is distance between teeth and $L_1$ is a shell length. For biological minimum size(25mm) of venus clam to be catchability 50% the distance between teeth was estimated 16.2mm from the logistic curve. Therefore it is desirable to extend that current spacing between teeth from 12mm to 16mm for the venus clam dredge. That space increasing enables fuel oil of vessel to drag a dredge to be reduced and also man power to sift through sifter smaller venus clams on boards to be reduced.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.254-254
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• 2011

The memories with nano-particles are very attractive because they are promising candidates for low operating voltage, long retention time and fast program/erase speed. In recent, various nano-floating gate memories with metal-oxide nanocrystals embedded in organic and inorganic layers have been reported. Because of the carrier generation in semiconductor, induced photon pulse enhanced the program/erase speed of memory device. We studied photo-induced electrical properties of these metal-oxide nanocrystal memory devices. At first, 2~10-nm-thick Sn and In metals were deposited by using thermal evaporation onto Si wafer including a channel with $n^+$ poly-Si source/drain in which the length and width are 10 ${\mu}m$ each. Then, a poly-amic-acid (PAA) was spin coated on the deposited Sn film. The PAA precursor used in this study was prepared by dissolving biphenyl-tetracarboxylic dianhydride-phenylene diamine (BPDA-PDA) commercial polyamic acid in N-methyl-2-pyrrolidon (NMP). Then the samples were cured at 400$^{\circ}C$ for 1 hour in N atmosphere after drying at 135$^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was followed by using a thermal evaporator, and then the gate electrode was defined by photolithography and etching. The electrical properties were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. Also, the optical pulse for the study on photo-induced electrical properties was applied by Xeon lamp light source and a monochromator system.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.237.2-237.2
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• 2013

ReRAM cell, also known as conductive bridging RAM (CBRAM), is a resistive switching memory based on non-volatile formation and dissolution of conductive filament in a solid electrolyte [1,2]. Especially, Chalcogenide-based ReRAM have become a promising candidate due to the simple structure, high density and low power operation than other types of ReRAM but the uniformity of switching parameter is undesirable. It is because diffusion of ions from anode to cathode in solid electrolyte layer is random [3]. That is to say, the formation of conductive filament is not go through the same paths in each switching cycle which is one of the major obstacles for performance improvement of ReRAM devices. Therefore, to control of nonuniform conductive filament formation is a key point to achieve a high performance ReRAM. In this paper, we demonstrated the enhanced repeatable bipolar resistive switching memory characteristics by spreading the Ag nanocrystals (Ag NCs) on amorphous GeSe layer compared to the conventional Ag/GeSe/Pt structure without Ag NCs. The Ag NCs and Ag top electrode act as a metal supply source of our devices. Excellent resistive switching memory characteristics were obtained and improvement of voltage distribution was achieved from the Al/Ag NCs/GeSe/Pt structure. At the same time, a stable DC endurance (>100 cycles) and an excellent data retention (>104 sec) properties was found from the Al/Ag NCs/GeSe/ Pt structured ReRAMs.