• 한국분말재료학회지
• /
• 제2권1호
• /
• pp.29-35
• /
• 1995

In this study the calcined condition and characteristic of Cu-Ni-Zn ferrite powder were investigated. The Cu-Ni-Zn ferrite powder has been synthesized by the thermal decomposition of the organic acid salt. This process did not require a strict pH control and provided the uniform composition and fine powder with about 0.3 $\mu\textrm{m}$. The XRD diffraction pattern of this powder showed about 50% spinel phase. The optimum calcination was found to be done at $700^{\circ}C$ for one hour. After the calcination, the amount of spinel increased to 90%. The distribution of the particle size showed bimodal peaks, one was about 0.5 $\mu\textrm{m}$ and the other was about 20 $\mu\textrm{m}$. The large particles of 20 $\mu\textrm{m}$ were the agglomeration of fine Particles. The mean Particle size of the powder was about 0.4 $\mu\textrm{m}$. The powder was compacted under 100 MPa pressure and sintered at 1100~ $1250^{\circ}C$ for one hour in air. The density of ferrites specimen was a function of the sintering temperature. The higher the temperature, the denser the ferrite. The maximum relative density of the sintered ferrite was about 93% at $1250^{\circ}C$. The grain size of sintered specimen at $1200^{\circ}C$ was 5 $\mu\textrm{m}$ and homogeneous.

• 천문학회지
• /
• 제36권3호
• /
• pp.189-212
• /
• 2003

I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of $\approx$ 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (${\Delta}t{\approx}$ 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.

• 폴리머
• /
• 제36권6호
• /
• pp.693-698
• /
• 2012

본 연구에서는 높은 분자량의 polylactide(PLA)를 중합하기 위하여 aluminum isopropyl oxide($Al(O-i-Pr)_3$)를 아민기로 표면 기능화된 실리카에 담지하고 이를 촉매로 이용하여 생성된 PLA의 중합특성을 확인하였다. 담지촉매는 먼저 실리카 표면을 아민기를 갖는 실란화합물로 기능화한 후 $Al(O-i-Pr)_3$을 in-situ 합성하였다. 기능기에 담지된 $Al(O-i-Pr)_3$는 MAO(methyl aluminoxane) 존재하에 중합활성을 보였다. $115^{\circ}C$에서는 표면 기능화된 아민기양이 증가할수록 전환율과 분자량이 증가하였고, $130^{\circ}C$에서는 표면 기능화된 아민기양이 증가할수록 전환율은 감소하였으나 분자량은 크게 증가하여 표면 기능화된 아민기양이 3.0 mmol일 경우 44000 g/mol로 가장 높은 분자량을 얻었다. GPC curve를 통해 $115^{\circ}C$ 중합온도에서는 분자량 분포곡선이 bimodal 형태에서 저분자량 부분이 크게 증가하여 shoulder 형태로 변화하였으며 $130^{\circ}C$에서는 GPC 단일피크를 보였다. 균일계 $Al(O-i-Pr)_3$ 촉매보다 아민기로 표면 기능화된 실리카에 담지된 $Al(O-i-Pr)_3$ 촉매가 더 높은 활성과 고분자량의 PLA를 합성할 수 있었다.

• 한국대기환경학회지
• /
• 제23권6호
• /
• pp.675-688
• /
• 2007

To characterize organic and elemental carbon (OC and EC), and water-soluble organic carbon (WSOC) contents, daily $PM_{2.5}$ measurements were performed in August 2006 (summer) and Jan $11{\sim}Feb$ 12 2007 (winter) at an urban site of Gwangju. Daily size-segregated aerosol samples were also collected for WSOC analysis. No clear seasonal variations in EC and WSOC concentrations were observed, while seasonal differences in OC concentration, and OC/EC and WSOC/EC ratios were shown. The WSOC/OC ratio showed higher value in summer (0.56) than in winter (0.40), reflecting the greater enhancement of secondary WSOC formation at the site in summer. Secondary WSOC concentrations estimated using EC tracer method were in the range $0.0{\sim}2.1\;{\mu}g/m^3$ (average $0.42\;{\mu}g/m^3$) and $0.0{\sim}1.1\;{\mu}g/m^3\;(0.24\;{\mu}g/m^3)$, respectively, accounting for $0{\sim}51.6%$ (average 16.8%) and $0{\sim}52.5%$ (average 13.1 %) of the measured WSOC concentrations in summer and winter. Sometimes higher WSOC/OC ratio in winter than that in summer could be attributed to two reasons. One is that the stable atmospheric condition often appears in winter, and the prolonged residence time would strengthen atmospheric oxidation of volatile organic compounds. The other is that decrease of ambient temperature in winter would enhance the condensation of volatile secondary WSOC on pre-existing aerosols. In summertime, atmospheric aerosols and WSOC concentrations showed bimodal size distributions, peaking at the size ranges $0.32{\sim}0.56\;{\mu}m$ (condensation mode) and $3.2{\sim}5.6\;{\mu}m$ (coarse mode), respectively. During the wintertime, atmospheric aerosols showed a bimodal character, while WSOC concentrations showed a unimodal pattern. Size distributions of atmospheric aerosols and WSOC with a peak in the size range $0.32{\sim}0.56\;{\mu}m$ were observed for most of the measurement periods. On January 17, however, atmospheric aerosols and WOSC exhibited size distributions with modal peaks in the size range $1.0{\sim}1.8\;{\mu}m$, suggesting that the aerosol particles collected on that day could be expected to be more aged, i.e, longer residence time, than the aerosols at other sampling periods.

• 한국식품과학회지
• /
• 제19권4호
• /
• pp.371-376
• /
• 1987

쌀전분 및 이의 구성성분인 아밀로오스와 아밀로펙틴을 분리하여 이들의 분자 구조적 성질을 비교 검토하였다. 시료전분 및 아밀로오스와 아밀로펙틴의 고유점도는 각각 1.053, 1.772 및 0.919ml/g이었다. 또 쌀전분, 아밀로오스 및 아밀로펙틴의 ${\beta}-amylolysisimit$값은 각각 73, 106 및 56%이었으며 아밀로펙틴의 outer chain length$({\overline{OCL}})$)와 inner chain length $({\overline{ICL}})$은 각각 15.6 및 7.7로 두 chain길이의 비는 약 2 : 1이었다. 한편 전분은 pullulanase로 debranching한 후 sephadex G-75로 분획한 결과 두 개의 성분분획을 나타내었으며 void volume에서의 peak I은 주로 아밀로오스 그리고 ${\overline{dp}}$ 25-10에서의 peak II는 아밀로펙틴 성분이었다. 그러나 아밀로텍틴을 debranching한 후의 용출분포는 void volume에서 peak를 나타나지 않았으며 ${\overline{dp}}$ 35-25 및 ${\overline{dp}}$ 25-10에서 bimodal peak를 나타내었다. 또 pullulanase와 ${\beta}-amylase$를 동시에 처리한 경우는 ${\overline{dp}}$ 2-10에서 peak를 나타내었다.

• 해양환경안전학회지
• /
• 제29권6호
• /
• pp.525-535
• /
• 2023

본 연구는 2003년부터 2022년까지 동해 남서부 해역에서 초미소(0.2-2 ㎛) 식물플랑크톤의 군집, 표층 수온 상승, 그리고 무기 영양염 간의 복잡한 상호작용을 다루었다. 동해에서 관측된 표층 수온의 상승 추세는 전 지구규모의 수온 상승과 일치하며, 여름에는 최대 온도가 나타나지만 봄에는 최소 온도를 보여 일반적인 온대해역의 계절적 수온 변동과는 다른 양상을 보였다. 표층 무기 영양염의 농도는 겨울에 증가하며 봄을 거치면서 서서히 감소하는 계절적 변동성을 나타냈다. 식물플랑크톤의 생물량을 대표하는 표층 총 chlorophyll-a 농도는 온대 해역의 전형적인 쌍봉분포(bimodal distribution) 양상을 보였다. 연구 기간 동안 초미소 식물플랑크톤의 기여도는 연평균 0.5%씩 지속적으로 증가하였으나, 총 chlorophyll-a 농도는 약한 감소 추세를 보였다. 초미소 식물플랑크톤의 기여도와 영양염 간에는 강한 상관관계가 나타났으며, 이는 이러한 변동이 식물플랑크톤의 크기별 영양염의 가용성과 밀접하게 연관되어 있음을 의미한다. 이러한 분석 결과는 해양 생태계의 변화 조건에서 식물플랑크톤이 어떻게 반응할는지 예측 가능하게 하므로, 생태학적으로 중요한 의미를 갖는다.

• 한국대기환경학회지
• /
• 제25권6호
• /
• pp.550-561
• /
• 2009

This study is to investigate the air pollution characteristics of an industrialized midsize west-coastal city by comparing air quality to a neighboring inland city. The hourly averaged data of $O_3$, $SO_2$, $NO_2$, CO, and $PM_{10}$ measured from continuous air quality monitoring sites in Gunsan (coastal) and Jeonju (inland) were analyzed. The data set covers the period from 2004 to 2006. The annual average concentrations of the air pollutants in two cities were compared in their abundances and temporal trends as well. $O_3$ and $SO_2$ in Gunsan were relatively higher than those in Jeonju, while vice versa in case of $NO_2$ and $PM_{10}$. It seems that heavy automobile emissions from Jeonju mainly bring on higher $NO_2$ and $PM_{10}$ than those in Gunsan on annual base. $NO_2$ concentrations in both cities showed bimodal diurnal variations with peaks in the morning and in the late evening. These peaks correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). Maximum hourly averages of $NO_2$ ranged from 18 ppb to 28 ppb at Jeonju, and from 12 ppb to 20 ppb at Gunsan. $O_3$ showed typical diurnal variation with a maximum in the afternoon between 14:00 and 16:00 LST. Diurnal variations of CO and $PM_{10}$ were similar to $NO_2$ while $SO_2$ was similar to $O_3$. Seasonal variations of $PM_{10}$ in both cities indicated that their concentrations during spring season were significantly high. Asian dust storms occur frequently during spring and seem to affect increase in $PM_{10}$. High $O_3$ and $PM_{10}$ days were selected from both cities. The analyses based on the HYSPLIT trajectory model during the high $O_3$ and $PM_{10}$ showed these episodes (six cases) were mostly coincident with Asian dust storm originated from northern China and Mongolia. However, these high air pollution episodes in the west coastal cities may not only be caused by the Asian dust but also affected by other air pollutants transported from China accompanying the Asian dust.

• 대한지리학회지
• /
• 제49권5호
• /
• pp.779-793
• /
• 2014

본 연구에서는 치악산 국립공원을 사례로 TCI를 이용하여 관광기후환경의 변화와 미래 전망을 파악하였다. 과거와 미래를 포함하여 분석된 모든 기간에서 TCI 일평균값의 분포는 봄철과 가을철에 두 개의 봉우리가 나타나는 이봉형태가 나타났다. 따라서 치악산 국립공원은 봄철과 가을철에 관광하기 가장 적합한 기후로 파악되었다. 이러한 분포에는 주간 쾌적지수(Cid)와 일쾌적지수(Cia)의 요소인 기온과 습도가 주요한 영향을 미치는 것으로 분석되었다. 최근 들어 치악산 국립공원의 여름철 관광기후환경이 저하된 것으로 분석되었다. 이는 일조시간의 감소가 이에 가장 큰 영향을 미친 것으로 나타났다. 미래로 갈수록 여름철 관광기후환경의 저하는 더욱 심화될 것으로 전망되었다. 또한 연중 가장 낮은 TCI는 현재 겨울철에 나타났지만 미래에는 여름철로 변화할 것으로 분석되었는데 이는 세부지수 중 주간 쾌적지수(Cid)의 감소가 가장 큰 기여를 하였다.

• 한국환경과학회지
• /
• 제13권4호
• /
• pp.377-387
• /
• 2004

This study has been performed to clarify the characteristics of temporal and spatial distribution of surface ozone concentration over Jeju Island, one of the cleanest areas in Korea with low emissions of air pollutants. Ozone data are monitored at four sites in Jeju Island. These monitoring sites are located at two urban area(referred to Ido and Donghong), coastal area(Gosan site) and forest site(Chuna site). Ozone data has been routinely collected at these sites for the late four years. The patterns of seasonal cycle of ozone concentrations at all stations show the bimodal with the peaks on spring and autumn and a significant summer minimum. However, the patterns of diurnal variations at rural station, i.e., Gosan and Chuna sites are considerably different to those at urban stations such as Ido and Donghong sites. The patterns of $\DeltaO_3$ variations are very similar with those of monthly mean ozone concentrations and $\DeltaO_3$ values are exceeded 30 ppb, at urban stations. This may be that urban stations are more influenced by local photochemical reactions rather than rural stations. In order to assess the potential roles of meteorological parameters on ozone formation, the meteorological parameters, such as radiation, temperature, and wind are monitored together with ozone concentrations at all stations. The relationships of meteorological parameters to the corresponding ozone concentration are found to be insignificant in Jeju Island. However, at Gosan and Donghong stations, when the sea breeze blew toward the station, the ozone concentration is considerably increased.

• Journal of Korean Society for Atmospheric Environment
• /
• 제22권E1호
• /
• pp.35-43
• /
• 2006

Ambient particle size distributions of PCBs and their dry deposition fluxes were measured at a site in Seoul to quantify dry deposition fluxes of PCBs and size characteristics of PCBs in the air, and to estimate ambient concentrations of gaseous PCBs and dry deposition fluxes. The dry deposition plate was used to measure dry deposition fluxes of particulate mass and PCBs and a cascade impactor and rotary impactor were used to measure ambient particle size distributions for small ($D_p<9{\mu}m$) and large ($D_p>9{\mu}m$) particles, respectively. Six sample sets were collected from April to July 1999. The fluxes of particulate total PCBs (the sum of 43 congeners) ranged from 160 to $607ng\;m^{-2}day^{-1}$. The size distribution of total PCBs was bimodal with two peaks in small particle size ($D_p{\sim}0.6\;and\;6{\mu}m$, respectively) and, thus, mass concentration being dominant in small particles. The mean particulate PCBs concentration was $6.9{\mu}g$ PCBs/g. The concentrations of PCB homologues in the gas phase were estimated based on the particle/gas partition coefficient ($K_p$) with the measured values of particulate PCBs in this study and they were comparable to those observed in other previous studies. Dry deposition fluxes were estimated by calculating dry deposition velocities.