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Coarse woody debris mass dynamics in temperate natural forests of Mt. Jumbong, Korea
윤태경,정혜근,김래현,노남진,서경원,이수경,조우용,손요환 한국생태학회 2011 Journal of Ecology and Environment Vol.34 No.1
Coarse woody debris (CWD) mass dynamics in three temperate natural forests, dominated by Quercus mongolica, Abies holophylla, and Pinus densiflora, were studied for 5 to 8 years in a Korea National Long-Term Ecological Research (KNLTER) site located in Mt. Jumbong, Korea. CWD mass (Mg/ha), input rate of CWD mass (Mg ha^(-1) y^(-1)), and decay rate constant (1/y) were 20.6, 1.20, and 0.058 for Q. mongolica forest, 12.2, 0.44, 0.106 for A. holophylla forest, and 5.0, 0.00, and 0.086 for P. densiflora forest, respectively. CWD mass was classified into species, types (log, snag, and stump), and decay classes (I-V). The proportion of logs was higher than that of the other CWD types in Q. mongolica forest because of wind-related mortality, whereas the proportion of logs was similar to the proportion of snags in A. holophylla forest and P. densiflora forest. CWD mass, input rate, decay rate, and distribution reflected the status of forest regeneration and succession for three forests. Mass dynamics were affected interactively by a variety of factors including species, microclimate, and topography, but these effects were hardly distinguishable in this study because of the limited number of comparable sites and pieces of CWD. Thus, further studies will require data regarding long-term microclimate and CWD mass dynamics in a variety of forest types, which could represent diverse environmental factors.
Byungwoo Kim,정혜근,Byoung Koun Min,김홍곤,김웅 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.12
We demonstrate that vertically aligned carbon nanotubes can be synthesized directly on tantalum substrate via waterassisted chemical vapor deposition and evaluate their properties as electrochemical capacitors. The mean diameter of the carbon nanotubes was 7.1 ± 1.5 nm, and 70% of them had double walls. The intensity ratio of G-band to D-band in Raman spectra was as high as 5, indicating good quality of the carbon nanotubes. Owing to the alignment and low equivalent series resistance, the carbon nanotube based supercapacitors showed good rate performance. Rectangular shape of cyclic voltammogram was maintained even at the scan rate of > 1 V/s in 1 M sulfuric acid aqueous solution. Specific capacitance was well-retained (~94%) even when the discharging current density dramatically increased up to 145 A/g. Consequently, specific power as high as 60 kW/kg was obtained from as-grown carbon nanotubes in aqueous solution. Maximum specific energy of ~20 Wh/kg was obtained when carbon nanotubes were electrochemically oxidized and operated in organic solution. Demonstration of direct synthesis of carbon nanotubes on tantalum current collectors and their applications as supercapacitors could be an invaluable basis for fabrication of high performance carbon nanotube supercapacitors.
Facile Synthesis of Silver Chloride Nanocubes and Their Derivatives
Seungwook Kim,정혜근,Jong Hwa Kwon,윤호규,김웅 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.10
We demonstrate a facile route to synthesize silver chloride nanocubes and derivative nanomaterials. For the synthesis of silver chloride nanocubes, silver nitrate and hydrochloric acid were used as precursors in ethylene glycol, and poly (vinyl pyrrolidone) as a surfactant. Molar ratio of the two precursors greatly influenced the morphology and composition of the final products. As-synthesized silver chloride nanocubes showed size-dependent optical properties in the visible region of light, which is likely due to a small amount of silver clusters formed on the surface of silver chloride nanocubes. Moreover, we show for the first time that simple reduction of silver chloride nanocubes with different reducing reagents leads to the formation of delicate nanostructures such as cube-shaped silver-nanoparticle aggregates, and silver chloride nanocubes with truncated corners and with silver-nanograin decorated corners. Additionally, we quantitatively investigated for the first time the evolution of silver chloride nanocubes to silver chloride nanocubes decorated with silver nanoparticles upon exposure to e-beam. Our novel and facile synthesis of silver chloride related nanoparticles with delicately controlled morphologies could be an important basis for fabricating efficient photocatalysts and antibacterial materials.
Bacterial and fungal community composition across the soil depth profiles in a fallow field
고대근,유가영,윤성택,전성천,정혜근 한국생태학회 2017 Journal of Ecology and Environment Vol.41 No.9
Background: Soil microorganisms play key roles in nutrient cycling and are distributed throughout the soil profile. Currently, there is little information about the characteristics of the microbial communities along the soil depth because most studies focus on microorganisms inhabiting the soil surface. To better understand the functions and composition of microbial communities and the biogeochemical factors that shape them at different soil depths, we analyzed microbial activities and bacterial and fungal community composition in soils up to a 120 cm depth at a fallow field located in central Korea. To examine the vertical difference of microbial activities and community composition, β-1,4-glucosidase, cellobiohydrolase, β-1,4-xylosidase, β-1,4-N-acetylglucosaminidase, and acid phosphatase activities were analyzed and barcoded pyrosequencing of 16S rRNA genes (bacteria) and internal transcribed spacer region (fungi) was conducted. Results: The activity of all the soil enzymes analyzed, along with soil C concentration, declined with soil depth. For example, acid phosphatase activity was 125.9 (± 5.7 (± 1 SE)), 30.9 (± 0.9), 15.7 (± 0.6), 6.7 (± 0.9), and 3.3 (± 0.3) nmol g−1 h−1 at 0–15, 15–30, 30–60, 60–90, and 90–120 cm soil depths, respectively. Among the bacterial groups, the abundance of Proteobacteria (38.5, 23.2, 23.3, 26.1, and 17.5% at 0–15, 15–30, 30–60, 60–90, and 90–120 cm soil depths, respectively) and Firmicutes (12.8, 11.3, 8.6, 4.3, and 0.4% at 0–15, 15–30, 30–60, 60–90, and 90–120 cm soil depths, respectively) decreased with soil depth. On the other hand, the abundance of Ascomycota (51.2, 48.6, 65.7, 46.1, and 45.7% at 15, 30, 60, 90, and 120 cm depths, respectively), a dominant fungal group at this site, showed no clear trend along the soil profile. Conclusions: Our results show that soil C availability can determine soil enzyme activity at different soil depths and that bacterial communities have a clear trend along the soil depth at this study site. These metagenomics studies, along with other studies on microbial functions, are expected to enhance our understanding on the complexity of soil microbial communities and their relationship with biogeochemical factors.