• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.363-369
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• 2016

Enhancing mechanical strength of concrete has been fascinated using carbon-based nanomaterials such as CNT and graphene. The key to improving strength is a dispersion of nanomaterials. A novel method is required to investigate the dispersion inner concrete nondestructively. In this study, the optical optical properties such as refractive index and absorption coefficient are measured in nano-cement mortar specimens containing MWCNT and GO using THz electro-magnetic waves. From the results, the properties of nano-cement mortar are confirmed to be 1.0% to 2.5% higher in refractive index, and -14% to 28% higher in absorption coefficient than those of cement mortar at the average values. Using these characteristics, visualizing the dispersion of nano-concrete structures seems possible in future.

• Korean Chemical Engineering Research
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• v.48 no.4
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• pp.423-427
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• 2010

Carbon nano sphere(CNS) and nano bowl of carbon(NBC) containing 1.0 wt% copper were prepared by impregnation method and their catalytic activity was compared in the phenol hydroxylation with hydrogen peroxide in the presence of water and acetonitrile as a solvent, respectively. Cu content of catalysts was determined by EDS, and BET, pore volume, pore size and pore size distribution were compared. For both catalysts, phenol conversion, $H_2O_2$ efficiency and yield of catechol and hydroquinone were higher in the presence of water as a solvent than those in the presence of actonitrile. And catalytic activity such as phenol conversion and $H_2O_2$ efficiency of 1.0 Cu/CNS is about two times higher than that of 1.0 Cu/NBC in water solvent.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.117-128
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical model. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.366-377
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• 2000

The development of proper joint model, which can describe real phenomena exactly and still can be used easily, is one of the most important element for the analysis of the mechanical and hydraulic behavior of discontinuous rock mass. In this study, an elasto-plastic constitutive model of joint behavior considering asperity degradation was extended with the concept of first and second order asperities. The proposed model was implemented to numerical code with discrete finite joint element. The parametric study with the various asperity angles and degradation coefficients showed that the model can reproduce the shear behavior of typical rough joints well. Results of laboratory monotonic and cyclic shear tests were compared with those of numerical tests to validate the model. The hydraulic model considering the relations between gouge production and aperture was introduced to the mechanical mode1. In an attempt to examine the performance of the model, comparative numerical test was conducted. Permeability between joint surfaces increased rapidly at the first stage, but became nearly constant with increasing shear displacement due to gouge production and uniform variation of aperture distribution.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.627-632
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• 2007

A fundamental study on the melt decontamination of metal wastes generated by dismantling the nuclear facility, the melting of metal wastes such as stainless steel and carbon steel have been carried out to investigate the distribution phenomena of the radioisotopes such as $^{60}Co$ and $^{137}Cs$ into the ingot, slag and dust phases by using the various slag types, slag concentration and basicity in an arc furnace. The $^{60}Co$ remained homogeneously in the ingot phase above 90 % and it was barely present in the slag below 10 %. The effect of the slag composition on the distribution for Co-60 was not considerable, but a basic slag former with high fluidity showed effective. $^{137}Cs$ was completely eliminated from the melt of the stainless steel as well as the carbon steel and distributed to the slag and the dust phase.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.707-713
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• 1998

The influence of plasma carburizing process on the surface hardness of SCM415 low-alloy steel (0.15% C) was investigated under the various process conditions of gas composition. gas pressure, plasma current density. temperature and time. The effective case depth was found to depend on the amount of methan gas containing carbon. thus the deepest case depth and the uniform hardeness were obtained with the 100% methan gas. The case depth increased with the plasma current density. The effective plasma carburizing temperature of SCM415 steel was found to be higher than 85$0^{\circ}C$, and the case depth was proportional to the square root of carburizing time under the same current density. The bending fatigue strength of the plasma carburized specimen is' higher than those of as- received specimen or reheat-quenched specimen.

• Journal of Korean Society of Forest Science
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• v.103 no.4
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• pp.593-598
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• 2014

In this study, we developed the carbon emission factors for 4 major species of warm-temperate region in Korea, and tried to provide their carbon emissions and removals estimates using these carbon emission factors. We selected Castanopsis cuspidata, Camellia japonica, Quercus acuta and Quercus glauca as target species and derived their carbon emission factors. The basic wood density that serve as one of the carbon emission factors were 0.583 for Castanopsis cuspidata, 0.657 for Camellia japonica, 0.833 for Quercus acuta and 0.763 for Quercus glauca and their uncertainties ranged from 5.3 to 17.9%. Biomass expansion factors were calculated as well: 1.386 for Castanopsis cuspidata, 2.621 for Camellia japonica, 1.701 for Quercus acuta and 2.123 for Quercus glauca and associated uncertainties varied from 14.7 to 30.5%. Lastly root-shoot ratios for each species were also determined: 0.454 for Castanopsis cuspidata, 0.356 for Camellia japonica, 0.191 for Quercus acuta and 0.299 for Quercus glauca with the uncertainties lying within a range from 19.8 to 35.7%. These three carbon emission factors including basic wood density had the uncertainties of less than 40% recommended by FAO. Therefore the application of country-specific emission factors seemed to provide quite accurate estimates of carbon emissions and removals. The estimation of the carbon stored in the 4 species were also conducted which amounted to $186.10tCO_2/ha$ for Castanopsis cuspidata, $280.63tCO_2/ha$ for Camellia japonica, $344.04tCO_2/ha$ for Quercus acuta and $278.91tCO_2/ha$ for Quercus glauca and their annual carbon removals were $6.65tCO_2/ha/yr$, $6.25tCO_2/ha/yr$, $11.70tCO_2/ha/yr$ and $12.29tCO_2/ha/yr$, respectively. This systematic assessment of forest resources can be a reliable source of information for managing evergreen broadleaved forest in warm temperate regions and thus serve as useful data for effective decision-making to address vegetation zone shifts due to climate change.

• Korean Journal of Ecology and Environment
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• v.36 no.4 s.105
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• pp.434-446
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• 2003

The fate and transport of many trace metals, metalloids, and radionuclides in porous media is closely linked to the biogeochemical reactions that occur as a result of organic carbon being sequentially degraded by different microorganisms using a series of terminal electron acceptors. The spatial distribution of these biogeochemical reactions is affected by processes that are often unique and/or characteristic to a specific environment. Generic model formulations have been developed and applied to simulate the fate and transport of arsenic in two hydrologic settings, permanently flooded freshwater sediments, namely non-vegetated wetland sediments and vegetated wetland sediments. The key physical processes that have been considered are sedimentation, effects of roots on biogeochemistry, advective transport, and differences in mixing processes. Steady-state formulations were applied to the sedimentary environments. Results of numerical simulations show that these physical processes significantly affect the chemical profiles of different electron acceptors, their reduced species, and arsenate as well as arsenite that will result from the degradation of an organic carbon source in the sediments. Even though specific biological transformations are allowed to proceed only in zones where they are thermodynamically favorable, the results show that mixing as well as abiotic reactions can make the profiles of individual electron acceptors overlap and/or appear to reverse their expected order.

• Journal of Wetlands Research
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• v.25 no.4
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• pp.408-416
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• 2023

The IUCN Red List of Ecosystems serves as a global standard for assessing and identifying ecosystems at high risk of biodiversity loss, providing scientific evidence necessary for effective ecosystem management and conservation policy formulation. The IUCN Red List of Ecosystems has been designated as a key indicator (A.1) for Goal A of the Kunming-Montreal Global Biodiversity Framework. The assessment of the Red List of Ecosystems discerns signs of ecosystem collapse through specific criteria: reduction in distribution (Criterion A), restricted distribution (Criterion B), environmental degradation (Criterion C), changes in biological interaction (Criterion D), and quantitative estimation of the risk of ecosystem collapse (Criterion E). Since 2014, the IUCN Red List of Ecosystems has been evaluated in over 110 countries, with more than 80% of the assessments conducted in terrestrial and inland water ecosystems, among which tropical and subtropical forests are distributed ecosystems under threat. The assessment criteria are concentrated on spatial signs (Criteria A and B), accounting for 68.8%. There are three main considerations for applying the Red List of Ecosystems assessment domestically: First, it is necessary to compile applicable terrestrial ecosystem types within the country. Second, it must be determined whether the spatial sign assessment among the Red List of Ecosystems categories can be applied to the various small-scale ecosystems found domestically. Lastly, the collection of usable time series data (50 years) for assessment must be considered. Based on these considerations, applying the IUCN Red List of Ecosystems assessment domestically would enable an accurate understanding of the current state of the country's unique ecosystem types, contributing to global efforts in ecosystem conservation and restoration.

• Composites Research
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• v.24 no.4
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• pp.29-35
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• 2011

The characteristic length method used to determine a laminate's strength generally requires the test for un-notched and notched laminates and finite element analysis together. In this paper, the methods used to predict the stress distribution and tensile characteristic length of open-hole laminates using the stress concentration factor and equivalent material properties are proposed. These methods do not require data on the failure load of open-hole laminates or finite element analysis. Once the stress and characteristic length have been determined, the failure load of the open-hole laminate can be calculated. The proposed method considers the effect of the material properties as a parameter and therefore can be applied to a variety of materials. The stress distribution is verified by comparing with a finite element analysis and test results. The predicted failure load shows a maximum deviation of 8% from the test results.