• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.10
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• pp.811-816
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• 2012

The effect of co-sputtering condition on the structural properties of $Mg_xZn_{1-x}O$ thin films grown by RF magnetron co-sputtering system was investigated for manufacturing ZnO/MgZnO structure LED. $Mg_xZn_{1-x}O$ thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The ZnO thin films have sufficient crystallinity on the high RF power. As RF power of ZnO target increased, the contents of MgO in the $Mg_xZn_{1-x}O$ film decreased. LED was manufactured using ZnO/MgZnO multi-layer on p-GaN/$Al_2O_3$ substrate. Threshold voltage of multi-layer LED was appeared at 8 V, and it was luminesced at wave length of 550 nm.

• Journal of Environmental Science International
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• v.14 no.3
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• pp.335-343
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• 2005

The objective of this research is to evaluate a feasibility of wastewater reuse by membrane treatment with vibrating membrane separation equipment. Molecular weight of compounds in wastewater, permeability of membrane and retentate characterization after membrane filtration were investigated in order to determine appropriate membrane pore size and materials for wastewater treatment. Selected membrane was evaluated with vibration membrane separation equipment to optimize operating conditions. The following conclusion are drawn. 1. We got as following test results after the distribution of particles in the semiconductor wastewater, are made up of $1\~20{\mu}m$. Si, gold and Al in turn are contained in semiconductor wastewater. 2. Recovery rate is changeless under increasing recovery rate in operation. Though a value can be if pressure can be changed, the highest value of permeate rate is presented in 150 psi. 3. The AS-100(polysulpone) was selected as the most appropriate membranes for the treatment of semi-conductor wastewater to VSEP system. The fouling almost did not occur during this experiments. The analyses of treated water with VSEP system showed conductivity: 0.059,us/cm, TDS: 40mg/l, COD: 20mg/l, SS : 5mg/l, n-Hexane: 8.3mg/l. Comparing previous systems, operating expenses is decreased by more $50\%$.

• Journal of Korean Society on Water Environment
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• v.21 no.5
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• pp.458-463
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• 2005

Considering the characteristics of a filtration bio-reactor equipped with a mesh filter module which can effectively maintain high concentration of biomass and enhanced solid-liquid separation performance, the hybrid process of filtration bio-reactor combined with coagulation was investigated to get improved filtration characteristics as well as water quality in this work. Two bio-reactors (Run-1 & Run-2) were operated under the following conditions: working volume of 25 L, continuous loading of a synthetic wastewater (BOD: 200 mg/L, T-N: 50 mg/L, T-P: 5 mg/L), where an appropriate amount of alum ($Al_2(SO_4)_3{\cdot}18H_2O$) was added once a day into the reactor (Run-2). In the system without using a alum (Run-1), the clogging of mesh filter module was observed two times through 85 days of whole operation. Meanwhile, the filter module did not clog even at higher MLSS concentration (6,000~12,000 mg/L) and the stable filtration (0.7 mid) was continued in the case of using a alum. Due to the stable formation of cake layers, BOD and SS were shown below 6 and 3 mg/L, respectively. T-P and pH of the effluent were changed because of the intermittent addition of the alum. In the case of Al/P=2.5, the average T-P removal efficiency per day was 85.2% and the average T-P concentration of the effluent was 0.3 mg/L. However, the removal efficiency of phosphate was influenced by pH in the reactor.

• Journal of the Korean Society for Environmental Technology
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• v.19 no.6
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• pp.556-562
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• 2018

Due to the enforcement of effluent water regulation the advance sewage treatment system is needed to retrofit and remodelling. In this case the most important issue is the effluent concentrations of TP and there are a lot of system to reduce its concentration. But biological treatment processes have many restrictions to enhance the removal efficiency of TP. In this study the efficient ECO operating condition to improve and retrofit biological sewage wastewater treatment system is as follow; 1) The treatment efficiency of BOD, TN and TP at the current density of $15mA/cm^2$ was higher than the treatment efficiency at $5mA/cm^2$ in the electrodes arranged with Al-SUS(Stainless Steel) regardless of the reaction time, The TP concentration was 0.1 mg/L or less. Especially, when the reaction time was maintained at 10 min, the TP concentration was 0.06 mg/L or less irrespective of the current density. 2) The change of TP concentration is not influenced by the change of current density and rather the concentration of treated water changes according to the reaction time. In the case of electro coagulation reaction, a few seconds to several minutes are required. However, the reaction time of electro coagulation and oxidation was studied to be more than 10 minutes. 3) As a result, it has been studied that the economical current density of the electro coagulation oxidation process for TN and TP treatment of domestic wastewater is $15mA/cm^2$ or less and the reaction time is 10 minutes.

• Journal of Radiation Protection and Research
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• v.43 no.4
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• pp.160-169
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• 2018

Background: This study aims to develop an integrated optical system that can simultaneously or selectively measure the signals obtained from radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL), which are luminescence phenomena of materials stimulated by radioactivity, heat, and light, respectively. The luminescence mechanism of various materials could be investigated using the glow curves of the luminescence materials. Materials and Methods: RL/TL/OSL integrated measuring system was equipped with a X-ray tube (50 kV, $200{\mu}A$) as an ionizing radiation source to irradiate the sample. The sample substrate was used as a heating source and was also designed to optically stimulate the sample material using various light sources, such as high luminous blue light emitting diode (LED) or laser. The system measured the luminescence intensity versus the amount of irradiation/stimulation on the sample for the purpose of measuring RL, TL and OSL sequentially or by selectively combining them. Optical filters were combined to minimize the interference of the stimulation light in the OSL signal. A long-pass filter (420 nm) was used for 470 nm LED, an ultraviolet-pass filter (260-390 nm) was used for detecting the luminescence of the sample by PM tube. Results and Discussion: The reliability of the system was evaluated using the RL/OSL characteristics of $Al_2O_3:C$ and the RL/TL characteristics of LiF:Mg,Cu,Si, which were used as dosimetry materials. The RL/OSL characteristics of $Al_2O_3:C$ showed relatively linear dose-response characteristics. The glow curve of LiF:Mg,Cu,Si also showed typical RL/OSL characteristics. Conclusion: The reliability of the proposed system was verified by sequentially measuring the RL characteristics of radiation as well as the TL and OSL characteristics by concurrent thermal and optical stimulations. In this study, we developed an integrated measurement system that measures the glow curves of RL/TL/OSL using universal USB-DAQs and the control program.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.98-98
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• 2003

초내열성 결정화유리는 전기전자부품, 천체만원경의 반사경, 직화용 조리기기, 군사용 부품 등에 광범위하게 이용되고 있는데 이중 LAS 계가 가장 오랫동안 알려진 조성 계이다. 이 결정화유리는 주입성형후 열처리에 의하여 결정상을 생성하여 사용되는데 표면이 매우 낮은 조도를 갖는 것으로 알려져 있으나 실제로는 제조상에 조도가 높게 나타나는 문제점이 제기되고 있다. 따라서 본 연구에서는 미세조직적인 측면에서 이러한 점을 연구하고자 Li$_2$O-AL$_2$O$_3$-SiO$_2$를 주성분으로 하고 소량의 MgO와 핵생성제로서 TiO$_2$, ZrO$_2$를 사용하여 시편을 제조하였다. 제조된 결정화유리의 결정화도의 차이에 따라 AFM, $\alpha$-STEP등으로 표면의 조도를 정량화였다. 결정상의 종류, 크기, 결정화도, 결정상간의 간격 등이 표면의 조도에 어떻게 영향을 주는가 에 대하여 연구한 결과를 제시하였다.

• Journal of Plant Biotechnology
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• v.44 no.2
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• pp.171-177
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• 2017

A callus-mediated regeneration protocol for sea-milkwort, an endangered coastal plant species in South Korea, is reported here. The explants of in vitro-plantlets generated from a node culture revealed distinguishable responses in callus induction depending on genotype, explant source, light condition, and 2,4-D concentration. Especially, continuous darkness exclusively facilitated callus induction from explants prior to other treatments. The calli initiated on the media with 2,4-D ranging from 0.1 mg/L to 3.0 mg/L in the dark vigorously proliferated when subcultured on the same media in continuous darkness. Given 1.0 mg/L zeatin in addition to darkness to the calli of the 'Pistachio' genotype, normal adventitious shoots were only regenerated from nodular structures that formed earlier from the calli at the frequency of 24.4 percent. Regenerated shoots easily grew into plantlets with roots and green color on a phytohormone-free MS medium under lighted condition, that were used for node culture as plant materials. Node culture effectively multiplied plantlets in accordance with protocol by Bae et al. (2016). Acclimatized plantlet clusters developed mature plant clusters under inland environment, followed by flowering the following April. Results were merged with node culture protocol suggested by Bae et al. (2016), which, as an in vitro propagation system for sea-milkwort, may contribute to natural habitat restoration.

• Journal of Welding and Joining
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• v.21 no.1
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• pp.107-113
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• 2003

Joining of $Si_3N_4$ to $Si_3N_4$ with crystallized glass solder was studied. $SiO_2-Al_2O_3-MgO$ glass with $P_2O_5$ as a crystallizing reagent was used as a solder. To improve the hish temperature toughness of joined specimen, two stage heat treatment was applied to Joined sample for the crystallization of joined layer, Two factors, i.e. thickness of soldered layer and crystallization were taken and thier effects on joining strength were investigated by a SEM-EDX observation of joined interface and bending strength both at room and elevated temperatures. Obtained results are summarized as follows: (1) Nitrogen diffused from $Si_3N_4$ to solder during the Joining process. Average amount of nitrogen in soldered layer depended on the thickness of the soldered layer and increased with decrease of the thickness. (2) Joining strength of the specimen having a thinner soldered layer was stronger than that of thicker layer. This can be mainly attributed to the difference of the nitrogen content in the soldered layer. (3) Higher content of nitrogen in solder brought forth higher viscosity of the solder. Hence the crystallization of the solder become more difficult in thinner layer of the solder than thicker one. (4) Thus, the effect of crystallization was evaluated mostly by the thicker layer specimen. Crystallization of soldered layer improved markedly the fracure strength of joining at higher temperatures than the softening temperature of glass solder.

• The Journal of Engineering Research
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• v.1 no.1
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• pp.15-22
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• 1997

The crystallization behaviours of cordierite gel derived from sol-gel method and glass prepared from conventional melting method with or without $TiO_2$ as nucleants are compared. The densification temperature of gel is $810^{\circ}C$ and its chemical structure identified by IR analysis is same as that of glass melted by conventional method. The beginning crystallization temperature of gel is $965^{\circ}C$ lower than that of melted glass with 10wt% $TiO_2$, which is $978^{\circ}C$. The crystalline phases developed from gel during heat treatment are identified as spinel, $\beta$-quartz solid solution and $\alpha$-cordierite crystal and crystalline phases in case of glass are (Mg,Al)TiOn and $\beta$-quartz solid solution and $\alpha$-cordierite crystal, respectively. The crystallization in melted glass with nucleants occurs through bulk crystallization and in case of that without nucleants surface crystallization occurs, while the crystallization in gel is internal crystallization from interface between particles formed after densification.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.2
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• pp.58-61
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• 2002

Photoluminescence up-conversion in semiconductor heterostructures is a phenomenon in which luminescence occurs at energies higher than that of the excitation photons. It has been observed in many semiconductor heterostructure systems, including InP/AnALAs, CdTe/CdMgTe, GaAs/ordered-(Al)GalnP, GaAs/AIGaAs, and InAs/GaAs. In this wort, GaAs/AIGaAs heterostructures are used as a model system to study the mechanism of the up-conversion process. This system is ideal for testing different models because the band offsets are quite well documented. Different heterostructures are designed to study the effect of disorder on the up-converted luminescence efficiency. In order to study the roles of different types of carriers, the effect of doping was investigated. It was found that the up-converted luminescence is significantly enhanced by p-type doping of the higher-band-gap material.