• Journal of Plant Biology
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• v.35 no.4
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• pp.317-322
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• 1992

The nitrogen fixation activity and environmental factors of Lespedeza bicli!oy Turcz, forming annual root nodules by symbiotic Rhizobium sp. were analyzed in the field conditions during the growing period. Seasunal changes of $N_2-fixation$ activity showed the maximum value of $120\;\mu\textrm{M}\;C_2_H4{\cdot}noduie\;g\;fw^{-1}{\cdot}hr^{-1}$ during the active growing period (June) and varied significantly depending on the growth phase and environmental factors. The maximum activities were attained at the conditions of pH 7, $30^{\circ}C$ of temperature, 18 Kpa of oxygen partial pressure and inhibited by water stress and nitrogen sources. The habitat soil was weak acidic and poor in nitrogen, phosphorus and organic matter contents. The leaf area ratios and chlorophyll contents were ranged from 442 to $48;\textrm{cm}^2{\cdot}g\;dw^{-1}$ and from 33 to $38\;\mu\textrm{g}\;chI{\cdot}\textrm{cm}^2$. Nitrogen contents in each organ showed the maximum of 46, 19 and $11\;mg{\cdot}g\;dw^{-1}, respectively for leaf, rool and stem in the early period. The highest phosphorus contents were 4.2, 1.2 and $0.6\;mg{\cdot}g\;dw^{-1}$, respectively for leaf. root and stem in early growing period. The allocation ratios of nitrogen quantity showed 60% for leaves and 73% for roots during the active and late growth period, and 22% [or stems in average. The allocalion ralios o[ phosphorus quantity showed 58% for leaves during the most productive period, 70% for roots in the pre-growth stage and 26% for stems in average.verage.

• Journal of the Korean Vacuum Society
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• v.2 no.3
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• pp.368-373
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• 1993

LCVD법에 의한 박막성장장치를 제작하였다. 제작한 CO2 레이저는 CO2 : N2 : He이 1 : 1 : 8로 혼합된 가스를 사용하였으며 최대 출력은 60W였고 혼합가스의 유량이 20l/min, 방전전류 40mAdlfEo 50W의 비교적 안정된 출력을 얻을 수 있었다. 반응실의 기초 진공은 1$\times$10-6torr였으며 레이저를 기판에 수직 혹은 수평으로 조사할 수 있도록 설계하였다. 제작된 장치로 SiH4 및 NH3를 재료로 하여 실리콘 및 quartz 기판위에 silicon nitride 박막을 증착하였다. 박막 생장시 가스를 흘리는 방식보다 가스를 채워놓고 하는 방식이 낮은 레이저 출력하에서 균일한 박막을 얻는데 효율적이라는 것을 발견하였다. 출력 55W의 레이저를 실리콘 기판에 5분간 조사하였을 때 최대 두께1.5$mu extrm{m}$의 박막을 얻었으며 quartz 기판위에는 출력 4W, 조사시간 6분에서 두께가 약 1$\mu\textrm{m}$인 비교적 균질의 박막을 얻을 수 있었다. FT-IR 및 XPS 분석 결과 SiH4와 NH3의 혼합비가 1 : 12일 때 비교적 nitride화가 잘 된 박막이 얻어졌음을 알았다.

• Journal of Korean Society for Atmospheric Environment
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• v.17 no.1
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• pp.19-29
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• 2001

Atmospheric concentrations of acidic pollutant were measured by the 4 stage filter pak method at Chunchon and by the 3 stage filter pack method at Seoul and Anmyon-do from January to December 1998. The sample was collected for 24 hours on every Wednesday. Concentrations of particulate matters were highest at Anmyon-do. The particulate concentration was much higher during the warm season than other seasons. While the particulate concentration was higher during the warm season, the concentration of gaseous matter was higher in winter. Dry deposition flux was calculated by using reported deposition velocities and concentration of pollutants measured in this study. The dry deposition velocities used in this study for SO$_2$, SO$_{4}^{2}$, HNO$_3$,NO$_{3}^{-}$ and NH$_3$ were 0.29, 0.15, 2.08( 2.13 only for Anmyon-do), 0.20 and 1.00cm/sec, respectively. At Chunchon, annual sulfur flux originated from dry deposition was 384 kg/$textrm{km}^2$, and the flux from wet deposition was 782kg/$textrm{km}^2$. Dry deposition of sulfur was 33% of total sulfur deposition. The annual nitrogen flux originated from dry deposition was 1,892kg/$textrm{km}^2$. And the flux from wet deposition was 1,066kg/$textrm{km}^2$. Dry deposition of nitrogen was 64% of total nitrogen deposition. Dry deposition as well as wet deposition have to be considerd in the study on acidification of environment such as soil or watershed.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.48 no.3
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• pp.179-183
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• 2003

In comparison of physicochemical properties between expanded rice hulls (ERH) and a commercial nursery soil (Bunong), the pH and content of organic matters were higher in ERH than those of Bunong soil. However, the content of available phosphate, $\textrm{NH}_4\textrm{-N}$ and $\textrm{NO}_3\textrm{-N}$ were lower in ERH as compared with Bunong soil. The growth characteristics of seedlings were evaluated for 15-day old seedlings grown in five different nursery soils including ERH. The plant height was the tallest (22.8cm) in Bunong soil and shortest (12.8cm) in ERH. There was no difference in number of leaves among five types of nursery soils. The best results based on the seedling quality and root intensity was obtained from the seedlings grown in the nursery soil which ERH was used for bedding and Bunong soil for covering in the seed tray. The weight of a seed tray with Bunong soils was 27% heavier than that of 'ERH + Bunong soil'.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.123-131
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• 1989

Hydroxyapatite powders were syntehsized by the reaction of Ca(NO3)2.4H2O and (NH4)2HPO4 in aqueous solution. The effect of the Ca/P mole ratio in the starting solution on the sintering of the powders and its microstructure was studied. When the Ca/P mole ratio in the starting solution was 1.69, the relative density of the sintered bodies was more than 95%. The sinterability was decreased as the Ca/P mole ratio in the starting solution was increased (Ca/P mole ratio >1.67). Hydroxyapatite sintered bodies obtained from the Ca/P mole ratio=1.69 had very excellent bending strength. The best bending strength was obtained at 110$0^{\circ}C$ and its value was 1220kg/$\textrm{cm}^2$. The average grain size was 0.277${\mu}{\textrm}{m}$. Most of sintered bodies were almost shown 100% hydroxyapatite phase. However, in case of the Ca/P mole ratio=1.64 hydroxyapatite was decomposed to $\alpha$-whitlockite above 120$0^{\circ}C$.

• Journal of Oral Medicine and Pain
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• v.21 no.2
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• pp.207-224
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• 1996

This study was designed to determine the most effective concentration of fluoride and energy density of laser irradiation for the anticarious effect. For this study surface hardness in enamel was measured before and after irradiation with pulsed Nd;YAG laser and the topical application of fluoride. Of the permanent mandibular anterior hovine teeth, healthy, carious free ones were used. Three hundred specimens were made. Specimens within 25~45 Vickers hardness numbers were assigned to 20 control and experimental stoops ; each containing 15 specimens. After forming artificial carious lesions, 10 J/$\textrm{cm}^2$, 20 J/$\textrm{cm}^2$, and 30 J/$\textrm{cm}^2$ energies were irradiated on the enamel surface of each experimental group. Also NaF, NH4F, Elmex gel(amine fluoride) and APF gel fluoride compounds were applied topically. Next, all the specimens were placed into the pH circulatory procedures for eight days. Vickers hardness numbers were measured using a microhardness tester. Surface changes of the enamel were observed using an scanning electron microscope. The comparative ana1ysis yielded the following results : 1. The reduction of surface hardness of the enamel surface was less in all groups with fluoride application than in the group without fluoride application. 2. The APF gel croup with 10 J/$\textrm{cm}^2$ irradiation showed the lowest reduction of surface hardness. 3. The reduction of surface hardness of the enamel surface in the group of laser irradiation without fluoride application not showed any significant difference according to the energy density of the laser. 4. Under the scanning electron microscope, in enamel irradiated with 10J/$\textrm{cm}^2$ showed appearance similar to acid etching surface. In enamel irradiated with 20 J/$\textrm{cm}^2$, line enamel crack was detected. In enamel irradiated with 30j/$\textrm{cm}^2$, severe enamel crack and fusion of enamel were detected. These results suggest that one could obtain the best anticariogenic effects without damage to teeth in the group of application of APF gel after laser irradiation with 10 J/$\textrm{cm}^2$.

• Proceedings of the Korean Aquaculture Society Conference
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• 2003.10a
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• pp.46-146
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• 2003

해양환경의 대표적 오염물질인 PAHs가 양식굴의 생리대사에 미치는 영향을 파악하고자, 서로 다른 PAHs 농도에 노출된 굴의 여수율, 호흡율, 배설율 및 동화율의 변화를 조사하였다. 부착생물을 깨끗하게 제거한 굴을 실험실로 옮겨 3일정도 순치시키고, 이후 각각의 0, 50, 100, 200ppb의 농도별로 약 10일간 미리 노출시켰다. 이후 각 개체별로 2L 들이 2$0^{\circ}C$항온수조에서 0.2$\mu\textrm{m}$ 여과해수를 사용하여 실험하였다. 여수율은 Chaetoceros simplex를 지표생물로 하여 수조내 시간당 감소율을 구하여 Kim(1995)의 식에 의해 구하였다. 호흡율은 유동파라핀으로 외부와의 공기접촉을 단절시키고, 수조내 단위시간당 DO meter로 산소변화를 측정하여 Widdows and Johnson(1988)의 식을 변형하여 계산하였다. 배설율은 단위시간동안 수조내 NH$_4$-N 농도 증가량으로 조사하였고, NH$_4$-N은 HACH Inc.에서 제공하는 측정법을 따랐다. 여수율은 500ppb에서 다소 영향을 받아 증가하였다. 호흡율과 배설율은 노출농도가 증가함에 따라 증가하였지만, 50ppb와 100ppb에서는 다소 차이가 없었다. 따라서 양식굴이 PAHs와 같은 오염물질에 노출되었을 경우, 초기에는 여수율의 변화는 없고 배설율과 호흡율이 상승하여 체내 에너지 요구량이 증가하는 것으로 생각된다.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1169-1177
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• 1995

Barium nitrate and yittrium nitrate were dissolved into distilled water. Titaium hydroxide precipitated from titanium chloride with NH4OH was dissolved into nitric acid. Each aqueous solution was mixed for 12 hr in the composition of Ba1-xYxTiO3 (x=0.1∼0.6) and the concentration of mixed solution was 0.1 mol/ι. The mixed solution was sprayed with an ultrasonic atomizer and carried into an electric furnace which was kept at 900∼1000$^{\circ}C$ and pyrolyzed. Pyrolyzed powders were collected on the glass filter with vacuum pump. Aqueous Mn solutiion was added into the synthesized powders, mixed with ultrasonic vibration and sintered at 1300∼1400$^{\circ}C$. Synthesized powders were characterized with SEM, XRD, DT-TGA, and BET. Microsture and resistivity of sintered body were investigated with SEM and multimeter. The results of this experiment were as follows; 1) Yittrium dooped BaTiO3 powders were synthesized above 950$^{\circ}C$. 2) The average particle sizes of powders from BET specific surface area and SEM were 0.045$\mu\textrm{m}$, 0.046$\mu\textrm{m}$ respectively. The particle size distribution was narrow in the range of 0.1∼1.0$\mu\textrm{m}$ from SEM. 3) Room temperature resistivity and pmax/pmin of 0.4 mol% Y doped specimen which was sintered at 1375$^{\circ}C$ were 102∼3 (Ω$.$cm) and 102∼3 respectively. 4) Room temperature resistivity and pmax/pmin of 0.4 mol% Y and 0.04 at% Mn added specimen which was sintered at 1375$^{\circ}C$ were 102∼3 (Ω$.$cm) and 106∼7 respectively. 5) Grain growth was inhibited with addition of Y2O3 and enhanced in addition of Mn by 0.05 atm%.

• Journal of the Korean Ceramic Society
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• v.34 no.10
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• pp.1083-1091
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• 1997

As one of the chemical powder fabrication methods, the powder preparation method by using oxalate has the following advantages; (1) easy to control the chemical stoichiometry, (2) easy to fabricate homogeneous and fine particles, and (3) easy to be thermaly decomposed at low temperature. In the present study, the initial morphology and size distribution of the powder were controlled and the homogeniaty was improved. By carefully controlling the pH with NH4OH, the Bi(Pb)-Sr-Ca-Cu-O superconducting powders were prepared and investigated for their properties. The microstructures and the superconducting properties of the pelletized samples were investigated. Also, the microstructures and electrical properties of the samples prepared by tape casting method were investigated. The fabricated powders were spherical with less than 400 nm, but most of them were agglomerated to be 1~3 ${\mu}{\textrm}{m}$ in size. The critical temperature of the pelletized sample annealed at 84$0^{\circ}C$ for 72 hours in air was 110K. And the critical currents of annealed samples in air prepared by tape casting process for 24 hours and 72 hours were 0.6 A (Jc=600A/$\textrm{cm}^2$) and 1.9A (Jc=1, 900A/$\textrm{cm}^2$) respectively.

• Journal of the Korean Ceramic Society
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• v.26 no.4
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• pp.493-498
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• 1989

High purity, submicron BaTiO3 powder was prepared by a hydrothermal technique using Ba(OH)2.8H2O, TiCl4 and NH4OH as starting raw materials. The submicron BaTiO3 powder was synthesized at 130~23$0^{\circ}C$ for 2.5h to yield highly crystalline particles with a narrow particle distribution. The mole ratio of Ba(OH)2.8H2O/TiO(OH)2 was 1.5. It is possible to obtain BaTiO3 with Ba : Ti=1.00$\pm$0/01. The samples densified well at 13$25^{\circ}C$, showing a uniform and fine grain structure. The grain size ranged between 0.3 and 0.5${\mu}{\textrm}{m}$. The products obtained by hydrothermal treatment at various temperatures from 130 to 23$0^{\circ}C$ were characterized by XRD, DTA, BET and SEM etc.