• The Korean Journal of Mycology
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• v.24 no.1 s.76
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• pp.8-16
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• 1996

The ${\alpha}-amylase$ of Alternaria alternata was purified through ammonium sulfate precipitation, dialysis and Sephadex G-100 column chromatography. One single band was obtained in SDS-polyacrylamide gel electrophoresis. The optimum pH for enzyme activity was 5.0 and the enzyme activity was maintained at $3.6{\sim}7.0$pH range. The optimum temperature for ${\alpha}-amylase$ activity was $40^{\circ}C$ and 71% of the activity was still maintained until 30 min after heating at $80^{\circ}C$. The ${\alpha}-amylase$ was slightly activated by $Mn^{2+},\;Zn^{2+}\;and\;Sn^{2+}$, but inhibited by $Ba^{2+},\;Pb^{2+},\;Co^{2+}\;and\;Ag^{1+}$. The $Hg^{2+}\;and\;Ag^{2+}$ slightly inhibited the activity of the enzyme at concentrations of $10^{-3}\;and\;10^{-4}M$. The Michaelis constant $(K_m)$ to soluble starch was $6.50{\times}10^{-2}M$ and inhibition constant $(K_i)$ by the 1mM EDTA was $8.0{\times}10^{-2}M$. The inhibition of this enzyme by EDTA was competitive one.

• Korean Journal of Environment and Ecology
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• v.18 no.2
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• pp.236-248
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• 2004

This study was carried out to propose improvement planting method by the research and analysis of planting concept, planting density, planting style and pattern in apartment complex, Seoul. Survey sites were selected by reflecting the change of green area ratio : Hawgok Jugong apartment complex, Gangseo-gu(1974), Samik-green apartment complex, Gangdong-gu(1980), Dongsindaea apartment complex, Gangseo-gu(1992). Green area in apartment complex was classified with front green area, side green area, and back-side green area. Planting concept that composed of landscape planting concept but anyother concept was not, was similar to all sites not differ from creation time. And planted species was not differ from planting style. Planting density was of both conopyㆍunder story layer was 0.0∼0.2 tree/$m^2$, and that of shrub layer was 0.0∼0.5 tree/$m^2$ Shrub layer planting density was insufficient and the density was not changed according to the creation time. Canopyㆍunderstory and shrub was planted to another green space, not concern with multi-layer structure. Planting pattern was utilized to single planting, linear planting, and random triangle planting, but it was not to the change that in each green space planting concept. Green area in apartment complex should be variety according to planting density, planting structure and planting pattern. And we should get the function of covering and beauty in case of front green space, that of ecological environment and increasing green volume in case of back-side green area, that of increasing green volume in case of side green area, apartment complex.

• Korean Journal of Remote Sensing
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• v.34 no.3
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• pp.519-533
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• 2018

The sensible heat flux (SHF)and latent heat flux (LHF) over Korean Peninsula ocean during recent 4 years were calculated using Coupled Ocean-Atmosphere Response Experiment (COARE) 3.5 bulk algorithm and satellite-based atmospheric-ocean variables. Among the four input variables (10-m wind speed; U, sea surface temperature; $T_s$, air temperature; $T_a$, and air humidity; $Q_a$) required for heat flux calculation, Ta and $Q_a$, which are not observed directly by satellites, were estimated from empirical relations developed using satellite-based columnar atmospheric water vapor (W) and $T_s$. The estimated satellite-based $T_a$ and $Q_a$ show high correlation coefficients above 0.96 with the buoy observations. The temporal and spatial variability of monthly ocean heat fluxes were analyzed for the Korean Peninsula ocean. The SHF showed low values of $20W/m^2$ over the entire areas from March to August. Particularly, in July, SHF from the atmosphere to the ocean, which is less than $0W/m^2$, has been shown in some areas. The SHF gradually increased from September and reached the maximum value in December. Similarly, The LHF showed low values of $40W/m^2$ from April to July, but it increased rapidly from autumn and was highest in December. The analysis of monthly characteristics of the meteorological variables affecting the heat fluxes revealed that the variation in differences of temperature and humidity between air and sea modulate the SHF and LHF, respectively. In addition, as the sensitivity of SHF and LHF to U increase in winter, it contributed to the highest values of ocean heat fluxes in this season.

• Journal of the Korean Vacuum Society
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• v.19 no.4
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• pp.307-313
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• 2010

One-dimensional cubic phase silicon carbide nanowires (${\beta}$-SiC NWs) were efficiently synthesized by thermal chemical vapor deposition (TCVD) with mixtures containing Si powders and nickel chloride hexahydrate $(NiCl_2{\cdot}6H_2O)$ in an alumina boat with a carbon source of methane $(CH_4)$ gas. SEM images are shown that the growth temperature (T) of $1,300^{\circ}C$ is not enough to synthesize the SiC NWs owing to insufficient thermal energy for melting down a Si powder and decomposing the methane gas. However, the SiC NWs could be synthesized at T>$1,300^{\circ}C$ and the most efficient temperature for growth of SiC NWs is T=$1,400^{\circ}C$. The synthesized SiC NWs have the diameter with an average range between 50~150 nm. Raman spectra clearly revealed that the synthesized SiC NWs are forming of a cubic phase (${\beta}$-SiC). Two distinct peaks at 795 and $970 cm^{-1}$ in Raman spectra of the synthesized SiC NWs at T=$1,400^{\circ}C$ represent the TO and LO mode of the bulk ${\beta}$-SiC, respectively. XRD spectra are also supported to the Raman spectra resulting in the strongest (111) peaks at $2{\Theta}=35.7^{\circ}$, which is the (111) plane peak position of 3C-SiC. Moreover, the gas flow rate of 300 sccm for methane is the optimal condition for synthesis of a large amount of ${\beta}$-SiC NW without producing the amorphous carbon structure shown at a high methane flow rate of 800 sccm. TEM images are shown two kinds of the synthesized ${\beta}$-SiC NWs structures. One is shown the defect-free ${\beta}$-SiC NWs with a (111) interplane distance of 0.25 nm, and the other is the stacking-faulted ${\beta}$-SiC NWs. Also, TEM images exhibited that two distinct SiC NWs are uniformly covered with $SiO_2$ layer with a thickness of less 2 nm.

• Solar Energy
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• v.13 no.2_3
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• pp.65-78
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• 1993

An overdose of fossil fuel for greenhouse heating causes not only the high cost and low quality of agricultural products, but also the environmental pollution of farm village. To solve these problems it is desirable to maximize the solar energy utilization for the heating of greenhouse in winter season. In this study phase change materials were selected to store solar energy concentratively for heating the greenhouse and their characteristics of thermal energy storage were analyzed. The results were summarized as follows. The organic $C_{28}H_{58}$, and the inorganic $CH_3COONa{\cdot}3H_2O\;and\;Na_2SO_4{\cdot}10H_2O$ were selected as low temperature latent heat storage materials. The equation of critical radius was derived to define the generating mechanism of the maximum latent heat of phase change materials. The melting point of $C_{28}H_{58}$ was $62^{\circ}C$, and the latent heat was $50.0{\sim}52.0kcal/kg$. The specific heat of liquid and solid phase was $0.54{\sim}0.69kcal/kg^{\circ}C$ and $0.57{\sim}0.75kcal/kg^{\circ}C$ respectively. The melting point of $CH_3COONa{\cdot}3H_2O$ was $61{\sim}62^{\circ}C$, the latent heat was $64.9{\sim}65.8$ kcal/kg and the specific heat of liquid and solid phase was respectively $0.83kcal/kg^{\circ}C$ and $0.51{\sim}0.52kcal/kg^{\circ}C$. The melting point of $Na_2SO_4{\cdot}10H_2O$ was $30{\sim}30.9^{\circ}C$, the latent heat was 53.0 kcal/kg and the specific heat of liquid and solid phase was respectively $0.78{\sim}0.89kcal/kg^{\circ}C$ and $0.50{\sim}0.7kcal/kg^{\circ}C$ When the urea of 21.85% was added to control the melting point of $Na_2SO_4{\cdot}10H_2O$ and the phase change cycles were repeated from 0 to 600, the melting point was $16.7{\sim}16.0^{\circ}C$ and the latent heat was $36.0{\sim}28.0kcal/kg^{\circ}C$.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.444-448
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• 2016

Hollow silicon/carbon (H-Si/C) composites as anode materials for lithium ion batteries were investigated to overcome the large volume expansion. H-Si/C composites were prepared as follows; hollow $SiO_2\;(H-SiO_2)$ was prepared by adding $NaBH_4$ to $SiO_2$ synthesized using $st{\ddot{o}}ber$ method followed by magnesiothermic reduction and carbonization of phenolic resin. The H-Si/C composites were analyzed by XRD, SEM, BET and EDX. To improve the capacity and cycle performance, the electrochemical characteristics of H-Si/C composites synthesized with various $NaBH_4$ contents were investigated by charge/discharge, cycle, cyclic voltammetry and impedance tests. The coin cell using H-Si/C composite ($SiO_2:NaBH_4=1:1$ in weight) in the electrolyte of $LiPF_6$ dissolved in organic solvents (EC : DMC : EMC = 1 : 1 : 1 vol%) has better capacity (1459 mAh/g) than those of other composition coin cells. It is found that the coin cell ($SiO_2:NaBH_4=1:1$ in weight) has an excellent capacity retention from 2nd cycle to 40th cycle.

• Applied Chemistry for Engineering
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• v.27 no.4
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• pp.397-401
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• 2016

A new solid oxidizer, pyridinium dinitramide (Py-DN) is a low toxic energetic material which can be utilized as a HPGP (high performance green propellant). In this work, Py-DN was synthesized using various starting materials including potassium sulfamate, pyridine hydrochloride, strong nitric acid and sulfuric acid. Physical and chemical properties of the Py-DN were characterized using UV-Vis, FT-IR and a thermal analyzer and their properties were compared to those of previously prepared salts including ammonium dinitramide[ADN, $NH_4N(NO_2)_2$] and guanidine dinitramide[GDN, $NH_2C(NH_2)NH_2N(NO_2)_2$] in our lab. Endothermic and exothermic decomposition temperatures of Py-DN were $77.4^{\circ}C$ and $144.7^{\circ}C$, respectively. The combustion caloric value was 1739 J/g, which is thermally more sensitive than that of conventional dinitramides. It may enable to lower the decomposition temperature, which can reduce preheating temperature required for satellite thruster applications.

• Journal of the Korean Geotechnical Society
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• v.21 no.6
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• pp.81-91
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• 2005

'Coarse grained material' refers to crushed stones or gravels, and the behaviour of soil containing coarse grained material is not easily defined using the conventional soil mechanics theory due to the influences of large particles, therefore large scale test is essential to investigate their effects. Previous studies have identified the major factors affecting the properties of coarse grained materials by using large scale shear testing apparatus, such as maximum particle size, water content, density and uniformity coefficients. In this paper, the effect of variation of maximum particle size and water content on shear strength was analyzed from the results of large scale shear test. In addition, the fiction coefficient at critical state per vertical load was estimated using the equation proposed by Wood (1998). The sample for the test was obtained from the local quarry sites. Tests results show that the shear strength for 50.8 m maximum particle size is relatively larger than that of 76.3 m and air-dry sample has larger shear strength than saturated sample. In the meantime, the friction coefficient at critical state shows $1.0\sim1.6$ according to the test conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.11
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• pp.927-933
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• 2016

In a solid propulsion system, the rocket nozzle is exposed to high temperature combustion gas. Hence, choosing an appropriate material that could demonstrate adequate performance at high temperature is important. As advanced materials, carbon/silicon carbide composites (C/SiC) have been studied with the aim of using them for the rocket nozzle throat. However, when compared with typical structural materials, C/SiC composites are relatively weak in terms of both strength and toughness, owing to their quasi-brittle behavior and oxidation at high temperatures. Therefore, it is important to evaluate the thermal and mechanical properties of this material before using it in this application. This study presents an experimental method to investigate the fracture behavior of C/SiC composite material manufactured using liquid silicon infiltration (LSI) method at elevated temperatures. In particular, the effects of major parameters, such as temperature, loading, oxidation conditions, and fiber direction on strength and fracture characteristics were investigated. Fractography analysis of the fractured specimens was performed using an SEM.

• Journal of Conservation Science
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• v.31 no.2
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• pp.159-173
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• 2015

The patternless potteries excavated from the Baekseokdong Gojaemigol site in Cheonan, was subdivided into talc and non-talc (including amphibole) type pottery. The potteries showed black, reddish brown and yellowish brown colors, but represent to difference with occurrences and internal texture of raw materials and temper minerals. The all potteries and paleosoils are commonly high content of temper minerals with poorly sorting and roundness of particles, and the paleosoils composed mainly of quartz, plagioclase, mica, chlorite and kaolinite. Between the talc and non-talc type potteries are very similar with magnetic susceptibility, absorption ratio and specific gravity. Geochemical behaviors of major, minor, compatible and incompatible elements in talc pottery are very similar with amphibole, non-talc pottery and paleosoils, and well correspondence with enrichment and deficiency patterns of each element, and the talc and amphibole potteries are highly enriched patterns of MgO concentration. In paleosoils of Gojaemigol site, talc and amphibole are not detected, therefore, making the pottery of the site estimate the possible to artificial additions of the temper minerals of talc and amphibole used interbedded talc layer within gneiss complex near the Baekseokdong area. Based on the phase relations, differential thermal and thermal gravimetric analyses, the potteries could be classified into two groups by firing temperature. The one group of talc temper pottery fired from 800 to $870^{\circ}C$ and the other group of amphibole and non-talc temper pottery revealed of 900 to $950^{\circ}C$.