• Journal of the Korean Vacuum Society
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• v.22 no.2
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• pp.79-85
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• 2013

Rare earth ions, either $Eu^{3+}$ or $Dy^{3+}$-doped $CaMoO_4$ phosphors were synthesized by using the solid-state reaction method. The crystalline structure of all the phosphor powders, irrespective of the type and concentration of activator ions, was found to be a tetragonal system with the main diffraction peak at (112) plane. For $Eu^{3+}$-doped $CaMoO_4$ phosphors, the grain particles showed an increasing tendency and the pebble-like patterns with a very homogeneous size distribution in the range of 0.01~0.10 mol of $Eu^{3+}$ ions concentration, and the excitation spectra were composed of a broad band centered at 311 nm and weak multiline peaked in the range of 360~470 nm. The dominant emission spectrum was the strong red emission centered at 618 nm due to the $^5D_0{\rightarrow}^7F_2$ transition of $Eu^{3+}$ ions. For $Dy^{3+}$-doped $CaMoO_4$ powders, excitation spectra showed a charge transfer band centered at 303 nm and relatively weak bands resulting from the transitions of $Dy^{3+}$ ions and the main yellow emission spectrum was observed at 578 nm, which was assigned to the $^4F_{9/2}{\rightarrow}^7H_{13/2}$ transition of $Dy^{3+}$ ions.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.190-199
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• 2012

The reproductive ecology of an endangered species, Gobiobotia macrocephala (Pisces: Cyprinidae), was investigated in the Seom River, a tributary of the Han River drainage system, from March 2010 to February 2011. During the non-spawning season, no difference in the external morphology was observed between males and females; however, during the spawning season, clear differences merged for the depth and width of the body, preventral length and preanal length in the standard length. The sex ratio of females to males was 1 : 1.01. The spawning season was estimated to last from late April to middle of June, at water temperatures of $15{\sim}25^{\circ}C$. The number of mature eggs in the ovary averaged about $2,134{\pm}930$ (mean${\pm}$SD), and the mean diameter was approximately $0.88{\pm}0.04$ mm. The spawning area was composed of pebble and cobble bottoms (3~10 cm), with current velocities of 13~24 cm $s^{-1}$ and water depths of 12~18 cm. Spawning behavior between males and females was observed in a water tank 14~15 h after injecting females with Ovaprim to promote reproduction. Fish spawned near the water surface with monogamous pairing.

• Journal of the Korean institute of surface engineering
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• v.50 no.4
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• pp.282-288
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• 2017

$Eu^{3+}$- or $Sm^{3+}$-doped $La_2MoO_6$ phosphors were synthesized with different concentrations of activator ions via a solid-state reaction. The X-ray diffraction patterns exhibited that crystalline structures of all the phosphors were tetragonal systems with the dominant peak occurring at (103) plane, irrespective of the concentration and the type of activator ions. The crystallites showed the pebble-like crystalline shapes and the average crystallite size increased with a tendency to agglomerate as the concentration of $Eu^{3+}$ ions increased. The excitation spectra of $Eu^{3+}$-doped $La_2MoO_6$ phosphors contained an intense charge transfer band centered at 331 nm in the range of 250-370 nm and three weak peaks at 381, 394, and 415 nm, respectively, due to the $^7F_0{\rightarrow}^5L_7$, $^7F_0{\rightarrow}^5L_6$, and $^7F_0{\rightarrow}^5D_3$ transitions of $Eu^{3+}$ ions. The emission spectra under excitation at 331 nm exhibited a strong red band centered at 620 nm and two weak bands at 593 and 704 nm. As the concentration of $Eu^{3+}$ increased from 1 to 20 mol%, the intensities of all the emission bands gradually increased. For the $Sm^{3+}$-doped $La_2MoO_6$ phosphors, the emission spectra consisted of an intense emission band at 607 nm arising from the $^4G_{5/2}{\rightarrow}^6H_{7/2}$ transition and three relatively small bands at 565, 648, and 707 nm originating from the $^4G_{5/2}{\rightarrow}^6H_{5/2}$, $^4G_{5/2}{\rightarrow}^6H_{9/2}$, and $^4G_{5/2}{\rightarrow}^6H_{11/2}$ transitions of $Sm^{3+}$, respectively. The intensities of all the emission bands approached maxima when concentration of $Sm^{3+}$ ions was 5 mol%. These results indicate that the optimum concentrations for highly-luminescent red and orange emission are 20 mol% of $Eu^{3+}$ and 5 mol% of $Sm^{3+}$ ions, respectively.

• Economic and Environmental Geology
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• v.50 no.5
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• pp.353-361
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• 2017

Uranium concentration in groundwater of the Goesan area was anticipated high because the area contains Ogcheon metamorphic rock zone which partly includes coal bed bearing high uranium content and nearly half of the area is covered by granitic rocks. Groundwater samples collected from 250 wells in five 5 lithology (Ogcheon meta-sandy rock zone (Og1), Ogcheon lower phyllite zone (Og2), Ogcheon pebble bearing phyllite zone (Og3), Jurassic granite (Jgr), Cretaceous granite (Kgr)), of the area were analyzed and equivalent uranium concentrations (e(U)) from 200 rocks near sampled wells were measured using portable gamma spectrometry. Higher median value of e(U) (8.2 mg/kg) was found on Kgr outcrops. The median e(U) value of Og2 was not as high as that of Kgr and similar to those of Jgr, Og1, and Og3 (3.05~3.90 mg/kg). The uranium level in groundwater of the area ranged from 0.01 to $293.0{\mu}g/L$ with a median value of $0.87{\mu}g/L$ which is similar to the national median uranium level of $0.74{\mu}g/L$. The uranium concentration was high in the samples from the Kgr (median $4.74{\mu}g/L$) and low samples from the Og1, Og2, and Og3 (median $0.35{\sim}0.74{\mu}g/L$). The percentage of total samples having uranium level above $30{\mu}g/L$ was 2.8%, on the other hand, that of Kgr is 20.7%, reflecting additional survey on the Kgr area is needed.

• Korean Journal of Ecology and Environment
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• v.44 no.2
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• pp.144-154
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• 2011

The fish community structure and inhabiting status of the endangered species Gobiobotia macrocephala and G. brevibarba were investigated at 10 stations in the Seom River, Korea from spring to autumn in 2010. During the survey, 37 species belonging to 10 families were found as inhabitants. A dominant species was Zacco platypus (36.2%), subdominant species were G. macrocephala (13.2%) and G. brevibarba (12.2%), and predominant species were Coreoleuciscus splendidus (8.1%) and Rhinogobius brunneus (4.9%). In addition, 18 species were endemic species to Korea; G. brevibarba and G. macrocephala were endangered species. The similarity index based on species composition and numbers clearly separated fish communities in the Seom River according to main sections, i.e., upper section (St. 1~3), middle section (St. 4~6) and lower section (St. 7~10). Dominance index gradually decreased toward the lower section, while diversity and species richness index gradually increased toward the downstream section. G. macrocephala resided in a fast-running downstream riffle with pebble and cobble substratum, while G. brevibarba inhabited the entire riffle with cobble substratum.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.242-254
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• 2010

Streams changed by artificial factor those support positive functions but also negative function to humanbeing. Time and pathway exceed the lost of structure and negative function appearing as disturbance. Therefore, it is desirable to prepare right situation to break of a vicious circle. Stream ecology was evaluated with using ichthyofauna during three years at the three disturbed sites and reference sites in Nakdong River. Forty-one species belonging three orders and ten families were identified in six surveying sites of Nakdong River during 2007~2009. Korean endemic species (14 species, 34.1%) and alien (3 species, 7.3%) were identified in Nakdong River ichthyofauna. Species number, species diversity, ecosystem structure and habitat variability of ecosystem were applied to evaluate stream ecosystem. In view of three year comprehended data at six sites; numeric instability appeared Andong Dam and Naeseongcheon sites worse than Gamcheon and reference site, otherwise more numeric diversity appeared Gamcheon and reference site than Andong Dam and Naeseongcheon. As a result of integration, sand stream including downstream of Andong dam, Naeseongcheon and Gamcheon has been having more diversified biodiversity and habitat diversity than those in the pebble stream.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.89-101
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• 2010

To constrain the depositional ages of the Gyeongsang sedimeantary formations, SHRIMP U-Pb ages were determined from detrital zircons in three samples: (1) a pebble-bearing sandstone from the lowermost Jinju Formation of the Sindong Group and (2) two conglomerates from the Silla Conglomerate of the Hayang Group. Their concordia ages are $112.4{\pm}1.3(2{\sigma})$ Ma and $110.4{\pm}2.0(2{\sigma})$ Ma respectively. Such ages represent the maximum deposition ages for the lowermost Jinju Formation and Silla Conglomerate, indicating the deposition of the Jinju Formation started from late Aptian and lasted to early Albian, then deposition of the rather thin Chilgok Formation and Silla Conglomerate was followed during the Albian. The age distribution of the analyzed detrital zircons indicates the presence of protoliths, or zircons derived from them, regarding a wide span of igneous activities from Mesozoic to Archean. Among such ages, there are Mesoproterozoic, Neoproterozoic and Paleozoic igneous activities, which have not been known or seldom reported from Korean peninsula. These ages further suggest the possible presence of rocks with such ages during the deposition periods or their derivation through a long river system developed into the continents at the time of deposition.

• Korean Journal of Environment and Ecology
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• v.24 no.1
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• pp.69-77
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• 2010

The Jeongdori windbreak forests of Wando island, located between the sea and the land, are very important as ecological succession areas that protect cultivated lands and fishing villages. Among the Jeongdori windbreak forests, the rocky seashore areas are occupied by Sageretia theezans mantle community, and their inner sections by sub-tree layers such as Ligustrum japonicum and Ligustrum obtusifolium. More specifically, the inner sections of the rocky seashore areas were found to be the habitat of Ligustrum japonicum-Quercus variabilis community, Ligustrum jarponicum-Viburnum erosum community, Ligustrum japonicum-Cinnamomum japonicum community, Cinnamomum japonicum-Carpinus tschonoskii community, and Pinus densiflora-Viburnum erosum community. The average height of tree layers of the Jeongdori windbreak forests is 10.3m, and the average diameter at breath height are 30.3cm. Though the windbreak forests was artificially made, it is now virtually natural forest and deserves protection for ecological reasons. Designated as a scenic spot 3, it is always in the danger of being damaged by frequent tourist visits. So the Jeongdori windbreak forest needs to be continuous maintenance and management by the National Park Service. Considering of the precious cultural treasures of the famous pebble stones covering Gugyedeung and the naturality of the Jeongdori windbreak forests, the Jeongdori windbreak forests as a scenic spot have to designated as the national monument in future and will preserve by the Cultural Properties Administration.

• Korean Journal of Ichthyology
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• v.27 no.4
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• pp.300-305
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• 2015

The characteristics of 11 spawning sites in the natural environment of the Korean endemic species, Liobagrus somjinensis were investigated in the Yocheon (stream) of Seomjingang (river), located in Sikjeong-dong, Namwon-si, Jeollabuk-do, Korea from May to June 2015. The spawning sites had largely two parts, the upper region close to the surface of the waters and under region at bottom: the upper part was covered with a large and flat boulder over about 256 mm in size, whereas the under part consisted mainly of pebbles and sand. The large boulder put on the upper region may be seen as a bulwark for guarding eggs laid at the under (bottom) region. All the sites under the boulder showed a similar structure having a small hollow filled with an egg mass and an individual (male). The spawning bottoms left clean having no any benthic invertebrates and detritus. The egg shape was spherical, yellow and covered with a transparent membrane and the egg size was $3.31{\pm}0.15mm$ (n=30) in diameter. The development stage of each egg mass under the boulder was almost same from morula stage to formation stage of eye lens. The average number of eggs in 11 spawning sites was $121{\pm}35.5$ (84~176) and the average number of female fecundity in ovary was $143{\pm}31.3$ (110~232).

• Korean Journal of Ichthyology
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• v.30 no.2
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• pp.100-106
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• 2018

The distribution aspect and extinction threat evaluation of the endangered species, Rhodeus pseudosericeus were investigated from 2012 to 2017 in Korea for the subject of this study. The number of appearance sites in the past literature of available and identified R. pseudosericeus was 26. During the study period, the samples of R. pseudosericeus were collected in 44 sites (Hangang River 35 sites, Sapgyocheon Stream 4 sites, Daecheoncheon Stream 5 sites) among the noted 214 sampling stations investigated. Among these, the newly appearance streams were Ilricheon Stream, Samsancheon Stream, Bangyecheon Stream and Hanpocheon Stream in the Hangang River. In addition, the habitats and populations in the upper Seomgang River (Hoengseong Dam), lower Heukcheon Stream, Muhancheon Stream and Daecheoncheon Stream decreased due to dam construction, river work, water pollution, and the spread of the exotic species Micropterus salmoides. The main habitat of R. pseudosericeus was the middle-upper stream of clean water with slow water velocity, sand-pebble bottoms and lots of aquatic plants. Given this evidence as noted for the 30.2% reduction in occupancy within 10 years, due to the qualitative decline of habitat, the overfishing risk of ornamental fish and the spread of M. salmoides, in this case R. pseudosericeus is considered to be Vulnerable (VU A2cde) based on the IUCN Red List categories and criteria.