• Journal of the Korean Vacuum Society
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• v.9 no.2
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• pp.150-154
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• 2000

We investigated the quantum well intermixing (QWI) of a compressively strained InGaAs/InGaAsP multiple quantum well (MQW) by using impurity free vacancy diffusion technique. The samples with InGaAs/$SiO_2$ capping layer showed a higher degree of intermixing compared to that of InP/$SiO_2$ capping layer after rapid thermal annealing (RTA). Band-gap shift difference as large as 123 meV (195 nm) was observed between samples capped with InGaAs/$SiO_2$ and with InP/$SiO_2$ layer at RTA temperature of $700^{\circ}C$. Using the InGaAs/$SiO_2$ cap layer, the band-gap wavelength of MQW was changed by the intermixing from 1.55 $\mu\textrm{m}$ band to 1.3 $\mu\textrm{m}$ band with a wavelength shift of a 237 nm. The transform from MQW structure to homogenous alloy was observed above the RTA temperature of $700^{\circ}C$.

• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.525-534
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• 2005

Adsorption experiments for As(V) and As(III) onto the surfaces of aerobic Pseudomonas aeruginosa, which can be readily isolated from natural media, were conducted under nutrient-absent conditions. While a small amount of As(III) was adsorbed on the bacterial cell surfaces, As(V) was not effectively removed from the solution through adsorption. The result was likely due to the electrostatic repulsion between anionic compounds of aqueous As(V) and cell surfaces of f aeruginosa. However, the bacteria forming biofilm reduced a large amount of aqueous As(V) to As(III), which indicated that microorganisms in most oligotrophic, natural geologic settings can mediate the behavior of aqueous As. Biobarriers designed to remove the various heavy metals in contaminant plume may practically lead to the enhancement of toxicity and mobility of As.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.3
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• pp.60-73
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• 1997

By introducing a compressive-strained quanternary InGaAsP quantum-wells instead of a conventional ternary InGaAs quantum-wells in 1.55.mu.m DFB-LD, the lasing performances canb e improved and the problems caused by the thickness non-uniformity and the compositional abruptness among the hetero-interpaces canb e relaxed. In this paper, we investigated an iptimum InGaAsP/InGaAsP multiple-quantum-well(MQW) structure as an active layer in a direct-modulated 1.55.mu. DFB-LD from the view point of threshold current, chirping charcteristics, and resonance frequency. The optimum compressive-strained MQW structure was revealed as InGaAsP/InGaAsP structure with strain amount of about 1.2%, number of wells $N_{w}$ of 7, well width $L_{w}$ of 58.agns.. The threshold current density J of 500A/c $m^{2}$, the linewidth enhancement factor a of 1.8, and differential resonance frequency of d $f_{r}$/d(I-I)$^{1}$2/=2GHz/(mA)$^{1}$2/(atI=2 $I_{th}$) were expected in 1.55.mu.m .gamma./4-shifted DFB-LD with the cavity length of 400.mu.m long and kL value of 1.25. These values are considerably improved ones compared to those of 1.55um DFB-LD with InGaAs/InGaAsP MQW which have enhancement factor and the resonance frequence frequency by the detuning of lasing wavelength and gain-peak wavelength. It was found that the linewidth enhancement factor of 20% and differential resonance frequency of 35% without the degradation of the threshold current density could be enhanced in the range of -15nm~-20nm detuning which can be realized by controlling the thickness and Incomposition of InGaAsP well. well.and Incomposition of InGaAsP well. well.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.31-36
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• 2003

We investigated dry etching of GaAs and AlGaAs in a high density planar inductively coupled plasma system with $BCl_3$ and $BCl_3/Ar$ gas chemistry. A detailed process study as a function of ICP source power, RIE chuck power and $BCl_3/Ar$ mixing ratio was performed. At this time, chamber pressure was fixed at 7.5 mTorr. The ICP source power and RIE chuck power were varied from 0 to 500 W and from 0 to 150 W, respectively. GaAs etch rate increased with the increase of ICP source power and RE chuck power. It was also found that etch rate of GaAs in $BCl_3$ gas with 25% Ar addition was superior to that of GaAs in a pure $BCl_3$ (20 sccm $BCl_3$) plasma. The result was same with AlGaAs. We expect that high ion-assisted effect in $BCl_3$/Ar plasma increased etch rates of both materials. The GaAs and AIGaAs features etched at 20 sccm $BCl_3$ and $15BCl_3/5Ar$ with 300 W ICP source power, 100 W RIE chuck power and 7.5 mTorr showed very smooth surfaces(RMS roughness < 2 nm) and excellent sidewall. XPS study on the surfaces of processed GaAs also proved extremely clean surfaces of the materials after dry etching.

• Analytical Science and Technology
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• v.13 no.2
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• pp.189-193
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• 2000

Arsenic (III) and arsenic (V) in disused mine tailing samples have been determined simutaneuously by hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES). Total arsenic was determined using 2% $NaBH_4$ and 6 M HCl after prereduction of As(V) to As(III) with) 1M KI. Arsenic (III) was determined selectively using citrate/citric acid buffer with range of pH 5-6, it was determined by HG-ICP-AES. Arsenic (V) can be evaluated by the differences. According to the results, arsenic (V) was over 90% among the total arsenic extracted from disused mine tailing samples.

• Applied Chemistry for Engineering
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• v.23 no.4
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• pp.394-398
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• 2012

Astragalin (AS), kaempferol monoglycoside, is classified as a polyphenol, and a minute quantity of AS is known to be present in several plants. Recently, it was reported that AS can be prepared by the partial hydrolysis of camelliaside A (CamA) and camelliaside B (CamB) in the tea seed extract (TSE) in the presence of a commercial enzyme complex such as Mash. In this paper, the effects of reaction temperature, amount of enzyme, and the substrate concentration on the reactivity were investigated. As the reaction temperature or the amount of enzyme increased, the reaction rate to produce AS increased, however, the hydrolysis of AS into KR was also enhanced. As a conclusion, the reaction, when 2 mL of Mash to 1 g of TSE was applied with a substrate concentration of 15% at $50^{\circ}C$, was found to be optimum, based on the reaction rate and the selectivity to AS.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.698-702
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• 2000

The characteristics of optical absorption in $Al_{0.24}Ga_{0.76}As/GaAs$ multi-quantum wells(MQWs) structure were investigated by using the surface photovoltage(SPV). The Spy features near 1.42 eV showed two overlapping signals. By chemical etching, we found associated with the GaAs substrate and the GaAs cap layer. The Al composition(x=24 %) was determined by Kuech's composition formula. In order to identify the transition energies. the experimentally observed energies were compared with results of the envelope function approximation for a rectangular quantum wells An amplitude variation of the relative Spy intensity from the GaAs substrate, llH, and llL was observed at different light intensities. A variation in the SPY line shape of the transition energies were observed with decreasing tempera­t ture.

• Korean journal of food and cookery science
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• v.15 no.4
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• pp.338-352
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• 1999

This research was carried to investigate the food preference of students, from elementary school, middle school, high school, university and industrial workers on Jinju, Sacheon and Jinyang by age and sex. The results were obtained as follows. In case of rice as the stationary food, plain white boiled rice showed the highest preference among all the groups. Most of groups liked most of one-dish meals such as kimbab, fried rice with kimchi, dumplings and bibimbab, especially the elementary school students and middle school students. On the other hand, high percentage of industrial workers disliked the western food such as pizza, hamburger and sphagetti. Most of subjects liked jajangmun, nangmun and bibimgooksu as noodles. As the side dishes generally they prefer the soup to stew. Male prefer the soup with beef and female prefer soup with vegetables. Stew with kimchi and stew with soybean paste showed high preference among most of groups. Most of broil food showed high preference, and students prefer meat to fish as broil cooking materials especially younger students. As a general they liked soybean sprout, spinach and wild sesame leaf as namul cooking method and they liked korean cabbage kimchi, chonggak kimchi, kackdoogi and dongchimi as kimchi. As a dessert subjects liked most of fruits and they liked yoghurt, fruit juice, milk, sikhae and soda as drinks generally. On the other hand snacks such as cooky, candy, cake, corn, rice cake, sweet potato have the lowest percentage preferance as a dessert, but students from elementary schools showed the highest preferance to sweet such as cooky, cake and candy than any other group. These food preferance results showed some nutritional problems especially young age students. They should eat more green-yellow vegetables, liver food and dried small sardine and they should reduce snacks such as candy and cooky and soda drinks. Therefore it is necessary to conduct nutrition education by parents, teachers and dietician together to improve their food habits and their health.

• Journal of the Korean Society of Food Science and Nutrition
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• v.26 no.4
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• pp.582-587
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• 1997

The changes of ascorbic acid(AsA) and dehydroascorbic acid(DHAA) contents in distilled water, carrot juice, and carrot+vegetable juices under different incubation time and temperature were determined by using high performance liquid chromatography. AsA in carrot juice was more stable than that in distilled water. AsA contents in distilled water and carrot juice were gradually reduced in a time and temperature dependent manner. AsA contents in carrot juice and carrot+ vegetable juices stored in refrigerator(4$^{\circ}C$) for 2 and 24 hours appeared to decrease, but the DHAA contents in all samples increased. Total vitamin C(AsA+DHAA) contents in carrot juice and carrot +vegetable juices remained with the high residue values of 90~97% after incubating at 4$^{\circ}C$ for 2 and 24 hours.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.378-382
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• 2018

It is a known fact that the cement production is responsible for almost 5% of total worldwide $CO_2$ emission, the primary factor affecting global warming. Geopolymers are valuable as ordinary Portland cement (OPC) substitutes because geopolymers release 80% less $CO_2$ than OPC and have mechanical properties sufficiently similar to those of OPC. Therefore, geopolymers have proven attractive to eco-friendly construction industries. Geopolymers can be fabricated from aluminum silicate materials with alkali activators such as fly ash, blast furnace slag, and so on. Integrated gasification combined cycle (IGCC) slag has been used for fabricating geopolymers. In general, IGCC slag geopolymers are fabricated with finely ground and sieved (<128 mesh) IGCC slag. The grinding process of as-received IGCC slag is one of the main costs in geopolymer production. Therefore, the idea of using as-received IGCC slag (before grinding the IGCC slag) as aggregates in the geopolymer matrix was introduced to reduce production cost as well as to enhance compressive strength. As-received IGCC slag (0, 10, 20, 30, 40 wt%) was added in the geopolymer mixing process and the mixtures were compared. The compressive strength of geopolymers with an addition of 10 wt% as-received IGCC slag increased by 19.84% compared to that with no additional as-received IGCC slag and reached up to 41.20 MPa. The enhancement of compressive strength is caused by as-received IGCC slag acting as aggregates in the geopolymer matrix like aggregates in concrete. The density of geopolymers slightly increased to $2.1-2.2g/cm^3$ with increasing slag addition. Therefore, it is concluded that a small addition of as-received IGCC slag into the geopolymer can increase compressive strength and decrease the total cost of the product. Moreover, the direct use of as-received IGCC slag may contribute to environment protection by reducing process time and $CO_2$ emission.