• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.14 no.3
• /
• pp.171-180
• /
• 2009

Based on the constituent analysis of sediments near Dok Island, the origin and sedimentary facies were Investigated. The sediments are mainly from originated from volcanic and volcaniclastic rock fragments derived from Dok Island and carbonate sediments formed by a variety of shallow-dwelling organisms that secreted calcareous skeletons. Carbonate producers include mollusks (bivalves and gastropods), encrusting & branching bryozoans, encrusting & segmented red algae, worm tubes, barnacles, diatoms, sponge spicules and echinoderm fragments. The distribution and relative amount of these constituents are basically dependent upon water depth and grain size even though local variations can be observed within the same depth interval. Five sedimentary facies can be divided: nearshore facies (<20 m), neritic facies ($20{\sim}100m$), upper transitional facies ($100{\sim}200m$), lower transitional facies ($200{\sim}700m$), and hemipelagic facies (>700 m). The sediments that were sampled below the water depth of 2,000 m still contain a significant amount of carbonates (ca. $10{\sim}20%$), implying that the carbonate compensation depth in the East Sea may well exceed this water depth.

• Proceedings of the KAIS Fall Conference
• /
• 2009.12a
• /
• pp.1034-1037
• /
• 2009

지구온난화룰 일으키는 온실가스중 하나인 이산화탄소를 제거하기 위하여 여러 가지 Epoxide와 이산화탄소를 Tetrabutylammonium bromide를 촉매로 하여 고압(900-1600psi), 고온($90^{\circ}C$)에서 반응시켜 고리형 카보네이트를 합성하였다. 합성된 고리형카보네트의 구조는 는 H-NMR, GC=MS, FT-IR을 이용하여 확인하였다.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.2
• /
• pp.622-624
• /
• 2014

• Macromolecular Research
• /
• v.16 no.7
• /
• pp.663-665
• /
• 2008

• Journal of the korean society of oceanography
• /
• v.33 no.3
• /
• pp.80-89
• /
• 1998

Three cores were taken from the northwest Pacific Ocean (Shikoku Basin) to determine the accumulation rates of both biogenic and terrigeneous fractions since the last penultimate interglacial period. The sediment is characterized by large amounts of terrigenous materials with low biogenic fractions and intermittent volcanic-ash layers, suggesting a hemipelagic origin. Composition of major elements shows no significant differences among sites. Relatively small variation of TiO$_2$/Al$_2$O$_3$ ratios with respect to SiO$_2$ content is the strong evidence for the common origin of terrigenous materials. The fraction of biogenic carbonates varies from near 0% in ash layers to about 35%, with a gradual increase toward the south (St. 4 through St. 6 to St. 20). However, carbonate contents show step-wise increasing tendency from St. 4 through St. 6 to St. 20, which suggests a southward increase of carbonate production. The color reflectance indicates that the sediment of the southern sites contains relatively higher amounts of biogenic carbonates. The mass accumulation rate of terrigenous fractions during the glacial period was 2-3 times higher than that of interglacial period. This enhanced mass accumulation rate of terrigenous materials was concomitant with the high accumulation rate of biogenic fractions. The total sediment accumulation rate is considered as the most important factor controlling mass accumulation rates of the biogenic and terrigenous materials. The enhanced sediment accumulation during the glacial periods is interpreted as a consequence of climate-induced change in the supply of eolian dust from the Asian continent. Enhanced wind strength during the glacial time may have increased transportation of terrigenous materials to the ocean. Thus, variation of sediment accumulation is highly linked with climatic variations.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.10
• /
• pp.3253-3257
• /
• 2012

Second-order rate constants for the reactions of phenyl Y-substituted-phenyl carbonates 5a-g with Z-substituted-phenoxides ($k_{Z-PhO^-}$) have been measured spectrophotometrically in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. 4-Nitrophenyl phenyl carbonate (5e) is up to 235 times more reactive than 4-nitrophenyl benzoate (4e). The Br$\o$nsted-type plot for the reactions of 5e with Z-substituted-phenoxides is linear with ${\beta}_{nuc}=0.54$, which is typical for reactions reported previously to proceed through a concerted mechanism. Hammett plots correlated with ${\sigma}^o$ and ${\sigma}^-$ constants for the reactions of 5a-f with 4-chlorophenoxide exhibit highly scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with ${\rho}_Y=1.51$ and r = 0.52, indicating that the leaving-group departure occurs at the rate-determining step (RDS). A stepwise mechanism, in which leaving-group departure occurs at RDS, has been excluded since the incoming 4-$ClPhO^-$ is more basic and a poorer nucleofuge than the leaving Y-substituted-phenoxides. Thus, the reaction has been concluded to proceed through a concerted mechanism. Our study has shown that the modification of the nonleaving group from benzoyl to phenyloxycarbonyl causes a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway) as well as an increase in the reactivity.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.7
• /
• pp.2023-2028
• /
• 2013

A kinetic study is reported for the nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5k) with piperidine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. [piperidine] for the reactions of substrates possessing a strong electron-withdrawing group (EWG) in the leaving group (i.e., 5a-5i) are linear and pass through the origin. In contrast, the plots for the reactions of substrates bearing a weak EWG or no substituent (i.e., 5j or 5k) curve upward, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. Thus, it has been suggested that the reactions of 5a-5i proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate (i.e., $T^{\pm}$) while those of 5j and 5k proceed through a stepwise mechanism with two intermediates (i.e., $T^{\pm}$ and its deprotonated form $T^-$). The slope of the Br${\o}$nsted-type plot for the second-order rate constants (i.e., $k_N$ or $Kk_2$) changes from -0.41 to -1.89 as the leaving-group basicity increases, indicating that a change in the rate-determining step (RDS) occurs. The reactions of 5a-5k with piperidine result in larger $k_1$ values than the corresponding reactions with ethylamine.

• The Korean Journal of Petroleum Geology
• /
• v.9 no.1_2 s.10
• /
• pp.1-15
• /
• 2001

Hierarchically controlled sequence stratigraphic analysis shows that the Lower Ordovician mixed carbonatesiliciclastic Mungok Formation, Korea consists of three depositional sequences: T1, T2, and T3 in ascending order. Sequence boundaries are generally marked by abrupt transition from coarse-grained shallow-water carbonates to finegrained deeper-water carbonates mixed with fine-grained siliciclastics, and show indication of subaerial exposure such as karstification. Within this sequence stratigraphic framework, facies characteristics indicate that the Mungok sequences were mostly deposited on a subtidal ramp without slope break. The Mungok ramp had been under the influence of frequent tropical storm activity during deposition. The difference in lithology of tempestites seems to have been controlled by the nature of substrates and by proximality. High-frequency cycles consist of upward-shallowing facies successions. Cycles of shallow-water and basinal deposits are not well represented, probably due to cycle amalgamation. Cycle stacking patterns do not show a consistent thickness change that is usually associated with a large-scale sea-level change probably because of unfilled accommodation space.

• Journal of Soil and Groundwater Environment
• /
• v.21 no.6
• /
• pp.87-100
• /
• 2016

Biochar, which has high alkalinity, has widely studied for amendment of soil that contaminated with heavy metals. The aim of this study is assessment of amendment for arsenic and heavy metals contaminated acidic agricultural soil using biochar that derived from buffalo weed (A. trifida L. var. trifida). Pot experiments were carried out including analysis of soil solution, contaminants fractionation, soil chemical properties and plant (lettuce) uptake rate. Arsenic and heavy metals concentrations in soil solution showed relatively low in biochar added experiments when compared to the control. In the heavy metals fractionation in soil showed decrease of exchangeable fraction and increase of carbonates fraction; however, arsenic fractionations showed constant. Soil chemical properties indicated that biochar could induce recovery of soil quality for plant growth in terms of soil alkalinity. However, phosphate concentration in biochar added soil decreased due to Ca-P precipitation by exchangeable calcium from biochar. Arsenic and heavy metals uptake rate of plant in the amended experiment decreased to 50% when compared to the control. Therefore biochar derived from buffalo weed can be used as amendment material for agricultural soil contaminated with arsenic and heavy metals. Precipitation of As-Ca and metal-carbonates are major mechanisms for soil amendment using char.

• Journal of Soil and Groundwater Environment
• /
• v.16 no.5
• /
• pp.31-41
• /
• 2011

The objectives of this study were to investigate the efficiencies of the stabilizers such as mono-potassium phosphate (MKP), phosphate fertilizer and red mud in treating the mine tailings contaminated with heavy metals and to characterize the changes in fractionations of the heavy metals during the stabilization. The TCLP results showed that the stabilization efficiencies of Cd, Pb and Zn increased with the increase in the stabilizer dosage and the reaction times. MKP showed the highest efficiencies for the heavy metals stabilization among the stabilizers tested. When the mine tailings were amended with MKP, the TCLP concentrations of Cd, Pb and Zn were reduced by 79~97%, 61~84%, and 89~99%, respectively. When the composite stabilizers, MKP/phosphate fertilizer or MKP/red mud, were used, the stabilization efficiencies were lower than when MKP was used as a single stabilizer. The sequential extraction results showed that carbonates fraction of Cd and Zn increased generally. Especially, when red mud was used, carbonates fraction of Cd and Zn increased 5 and 18 times, respectively. In the case of Pb, the treatment with MKP increased residual fraction by 10 times. The results showed that MKP was the most effective in stabilizing the heavy metals (Cd, Pb and Zn) to improve the efficacy of the composite binders.