• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.33-39
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• 2021

As the interest and demand in the recycled yarn field has increased rapidly worldwide, domestic companies are also promoting research and development and business on recycled yarn. The chemical and thermal properties of four types of virgin and recycled PET samples from A and B company, which are the leading domestic companies in the recycled polyester yarn business, were confirmed through infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Virgin and recycled PET from two companies were compared. FT-IR spectroscopy revealed the typical spectra of PET for both companies and a different peak at 872 cm-1. DSC confirmed that the melting point and crystallization temperature of recycled PET were lower than those of virgin PET. These results indicate that small amounts of contaminants are an important parameter affecting the thermal properties of recycled PET. In the DSC results after seven repeats of the heating and cooling processes, all four samples showed that a lower melting point, crystallization temperature, and low heat flow intensity increased with increasing number of cycles. The results of melting and crystallization enthalpy also showed similar patterns.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.99-106
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• 2006

In the present study, in order to clarify the effects of latent hydraulic property of granulated blast furnace slag (GBF slag) on the liquefaction, GBF slag was cured in the high temperature alkali water (adding the calcium hydroxide, pH=12, water temperature is about $30^{\circ}C$), and then the cyclic and the static tri-axial compression tests were carried out. Then the results were compared with those for Japanese standard sand of Toyoura sand and natural sand of Genkai sand. From the test results, it is clarified that the liquefaction strength of the GBF slag increases with the increase of the curing period by the hardening due to the latent hydraulic property. It is also shown that GBF slag with Dr=50% and 80% which was cured for 189 days in the fresh-water shows cohesion due to developing of latent hydraulic property. In addition, as for the liquefaction strength of GBFS during the hardening process, a linear relation between the cyclic stress ratio $R_{20}$ at the number of stress cycles Nc=20 and cohesion $C_{d}$ was observed. It is also clarified that the liquefaction strength for cured GBF slag in the high temperature alkali water is predicted by the cohesive strength or the unconfined compressive strength.

• Korean Journal of Agricultural and Forest Meteorology
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• v.25 no.2
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• pp.71-79
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• 2023

The quantification of soil respiration rates is important to understand carbon cycles of forest ecosystems. Soil respiration rates were assessed using Li-8100A soil flux system in one evergreen broadleaved (Quercus glauca Thunb.) and two coniferous (Cryptomeria japonica D. Don and Chamaecyparis obtusa Endl.) stands from May 2020 to April 2022 in southern Korea. Monthly variations of soil respiration rates were higher in the Q. glauca stand than in the C. japonica and the C. obtusa stands. The mean soil respiration rates were significantly higher in the Q. glauca stand (2.63µmol m^-2 s^-1) than in the C. japonica (0.93µmol m^-2 s^-1) and C. obtusa (0.99µmol m^-2 s^-1) stands. The three stands showed exponential relationships between soil respiration rates and soil temperature (R² = 0.44-0.80). The sensitivity of temperature (Q10 values) to soil respiration rates was highest in the Q. glauca stand (5.13), followed by the C. obtusa (3.10) and C. japonica (2.58) stands. These results indicate that soil respiration rates can be increased more in evergreen broadleaved stands than in coniferous stands under enhanced soil temperature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.41-53
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• 2008

Unprecedented weather phenomena are occurring because of climate change: extreme heavy rains, heat waves, and severe rain storms after the rainy season. Recently, the frequency of these abnormal phenomena has increased. However, regular pattern or cycles cannot be found. Analysis of annual data or annual average data, which has been established a research method of climate change, should be applied to find frequency and tendencies of extreme climate events. In this paper, extreme indicators of precipitation and temperature marked by objectivity and consistency were established to analyze data collected by 66 observatories throughout Korea operated by the Meteorological Administration. To assess the statistical significance of the data, linear regression and Kendall-Tau method were applied for statistical diagnosis. The indicators were analyzed to find tendencies. The analysis revealed that an increase of precipitation along with a decrease of the number of rainy days. A seasonal trend was also found: precipitation rate and the heavy rainfall threshold increased to a greater extent in the summer(June-August) than in the winter (September-November). In the meanwhile, a tendency of temperature increase was more prominent in the winter (December-February) than in the summer (June-August). In general, this phenomenon was more widespread in inland areas than in coastal areas. Furthermore, the number of winter frost days diminished throughout Korea. As was mentioned in the literature, the progression of climate change has influenced the increase of temperature in the winter.

• Journal of the Korean earth science society
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• v.22 no.5
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• pp.388-404
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• 2001

In order to examine the relative accuracy of satellite observations and model reanalyses about lower stratospheric temperature trends, two satellite-observed Microwave Sounding Unit (MSU) channel 4 (Ch 4) brightness temperature data and two GCM (ECMWF and GEOS) reanalyses during 1981${\sim}$1993 have been intercompared with the regression analysis of time series. The satellite data for the period of 1980${\sim}$1999 are MSU4 at nadir direction and SC4 at multiple scans, respectively, derived in this study and Spencer and Christy (1993). The MSU4 temperature over the globe during the above period shows the cooling trend of -0.35 K/decade, and the cooling over the global ocean is 1.2 times as much as that over the land. Lower stratospheric temperatures during the common period (1981${\sim}$1993) globally show the cooling in MSU4 (-0.14 K/decade), SC4 (-0.42 K/decade) and GEOS (-0.15 K/decade) which have strong annual cycles. However, ECMWF shows a little warming and weak annual cycle. The 95% confidence intervals of the lower stratospheric temperature trends are greater than those of midtropospheric (channel 2) trends, indicating less confidence in Ch 4. The lapse rate in the trend between the above two atmospheric layers is largest over the northern hemispheric land. MSU4 has low correlation with ECMWF over the globe, and high value with GEOS near the Korean peninsula. Lower correlations (r < 0.6) between MSU4 and SC4 (or ECMWF) occur over $30^{\circ}$N latitude belt, where subtropical jet stream passes. Temporal correlation among them over the globe is generally high (r > 0.6). Four kinds of lower stratospheric temperature data near the Korean peninsula commonly show cooling trends, of which the SC4 values (-0.82 K/decade) is the largest.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.288-296
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• 2019

Radiation cooling has used ceilings or floors as cooling surfaces. In such cases, to avoid moisture condensation on the surface, the surface temperature needs be higher than the dew point temperature or an additional dehumidifier is added. In this study, with a goal for residential application, intentional moisture condensation on the cooling surface was attempted, which increased the cooling capacity and improved the indoor comfortness. This method included two separate refrigeration cycles - convection-type dehumidifying cycle and the panel cooling cycle. Test results on the panel cooling cycle showed that, at the standard outdoor ($35^{\circ}C/24^{\circ}C$) and indoor ($27^{\circ}C/19.5^{\circ}C$) condition, the refrigerant flow rate was 8.8 kg/h, condensation temperature was $51^{\circ}C$, evaporation temperature was $8.8^{\circ}C$, cooling capacity was 376 W and COP was 1.75. Furthermore, the panel temperature was uniform within $1^{\circ}C$ (between $13^{\circ}C$ and $14^{\circ}C$). As the relative humidity decreased, the cooling capacity decreased. However, the power consumption remained approximately constant. In the convection-type dehumidification cycle, the refrigerant flow rate was 21.1 kg/h, condensation temperature was $61^{\circ}C$, evaporation temperature was $5.0^{\circ}C$, cooling capacity was 949 W and COP was 2.11 at the standard air condition. When both the radiation panel cooling and the dehumidification cycle operated simultaneously, the cooling capacity of the radiation panel cycle was 333 W and that of the dehumidification cycle was 894 W, and the COP was 1.89. As the fan flow rate decreased, both the cooling capacity of the radiation panel and the dehumidification cycle decreased, with that of the dehumidification cycle decreasing at a higher rate. Finally, a possible control logic depending on the change of the cooling load was proposed based on the results of the present study.

• Korean Journal of Materials Research
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• v.3 no.6
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• pp.624-631
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• 1993

The composites in the system aluminium titanate-mullite were synthesized by stepwise alkoxide hydrolysis of tetraethylorthosilicate, Si(OCLH5), and titaniumtetraethoxide, $Ti(OC_{2}H_{5})_4$ in $Al_{2}O_{3}$ ethanolic colloidal solution. All particles produced by sol-gel-process were amorphous, monodispesed and had a narrow particle size distribution. Sintered bodies at $1600 ^{\circ}C$ for 2h were subjected to prolonged durability tests-on the one hand annealing at the critical decomposition temperature of $1100 ^{\circ}C$ for lOOh and on the other cyclic thermal shock between 750 and $1400 ^{\circ}C$ for 100h. The best thermal durability was achieved by a composition containing 70 and 80 vol% aluminium titanate, which showed little change in microstructure and thermal expansion cycles during the tests. The microstructural degradation of samples studied using scanning electron microscopy, X-ray diffraction, and dilatometry, was presented here. The study was conducted in order to predict the service life of aluminium titanate-mullite ceramics formed by this processing route.

• Transactions of the Korean hydrogen and new energy society
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• v.5 no.2
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• pp.99-109
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• 1994

To develop high capacity hydrogen storage alloys for secondary Ni/MH batteries, electrochemical charge/discharge characteristics of $Zr_{1-x}Ti_xMn_{1-y}V_yNi_{1-z}M_z$ (M=Al,Co,Fe) alloys were investigated, in which $0.2{\leq}x{\leq}0.6$, $0.2{\leq}y{\leq}0.8$, $0.2{\leq}z{\leq}0.4$. With increasing Ti content(x) and/or decreasing V content(y), lattice constants and maximum theoretical capacities of the alloys were decreased and equilibrium pressure of hydrogen absorption were increased. Electrochemical discharge capacities were increased with increasing Ti content(x). Especially, the alloys of x= 0.4~0.6 showed better charge/discharge efficiencies than those of x<0.4. Discharge capacities of $Zr_{0.4}Ti_{0.6}Mn_{0.4}V_{0.6}Ni_{0.8}Fe_{0.2}$, $Zr_{0.4}Ti_{0.6}Mn_{0.4}V_{0.6}Ni_{0.8}Al_{0.2}$ and $Zr_{0.5}Ti_{0.5}Mn_{0.4}V_{0.6}Ni_{0.6}Co_{0.4}$ were 385, 328 and 333mAh/g, respectively. These alloys were fully activated within five charge/discharge cycles and had a good charge and discharge rate capabilities and temperature characteristics.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.5
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• pp.189-193
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• 2020

Recently, various methods for preparing a flexible electrode for implementing a wearable sensor have been introduced. Wearable sensors show similar tendency to use various polymer substrates, which provides elasticity suitable to the motion of human body. In this paper, a highly elastic silver nanowire based electrode was prepared on a sponge-based stretchable substrate, and electrical properties were evaluated. Silver nanowires were grown using a wet chemical synthesis, impregnated into a plasma-treated sponge, and then heat treated at a low temperature. In particular, the plasma surface treatment of the sponge enables uniform coating of silver nanowires. The flexible sponge electrode showed reliable electrical resistance changes over 160 repeated tensile-compression cycles.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.307.2-307.2
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• 2016

In this study, we synthesized Au nanoparticles (AuNPs) in polyacrylonitrile (PAN) thin films using a simple annealing process in the solid phase. The synthetic conditions were systematically controlled and optimized by varying the concentration of the Au salt solution and the annealing temperature. X-ray photoelectron spectroscopy (XPS) confirmed their chemical state, and transmission electron microscopy (TEM) verified the successful synthesis, size, and density of AuNPs. Au nanoparticles were generated from the thermal decomposition of the Au salt and stabilized during the cyclization of the PAN matrix. For actual device applications, previous synthetic techniques have required the synthesis of AuNPs in a liquid phase and an additional process to form the thin film layer, such as spin-coating, dip-coating, Langmuir-Blodgett, or high vacuum deposition. In contrast, our one-step synthesis could produce gold nanoparticles from the Au salt contained in a solid matrix with an easy heat treatment. The PAN:AuNPs composite was used as the charge trap layer of an organic nano-floating gate memory (ONFGM). The memory devices exhibited a high on/off ratio (over $10^6$), large hysteresis windows (76.7 V), and a stable endurance performance (>3000 cycles), indicating that our stabilized PAN:AuNPs composite film is a potential charge trap medium for next generation organic nano-floating gate memory transistors.