• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.660-665
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• 1999

Structure of water soluble chitosan (WSC) was confirmed by Fourier transform infrared spectrometer (FT-IR), X-ray diffractometer and thermal analyser. The viscosity average molecular weight of WSC ranged from $3.0{\times}10^{4}$ to $4.5{\times}10^{4}$. Using the WSC having viscosity average molecular weight of $3.0{\times}10^{4}$, the antimicrobacterial effects against microorganism and oral microorganism showed 81.7% and 80.6% for Staphyloccus aureus and Bacillus subtilis, respectively, while the anitmicrobacterial effect exhibited 100% and 73.8% against Streptococcus mutans and Streptococcus sanguis, respectively. Therefore it is concluded that WSC is more effective against oral microorganism that microorganism in terms of antimicrobacterial effects. WSC sample with the viscosity average molecular weight of $4.5{\times}10^{4}$ exhibited a half of the antimicrobacterial effect of the low MW sample, indicating that the WSC with low MW was better than that with high MW. Chitin and chitosan showed a drastic decrease of acidity from pH 7.0 to 4.9 after 8 minute incubation time and reached an equilibrium after that. WSC, however, restrained pH of the sample from lowering up to about 16 minutes of incubation and reached an equilibrium after that. WSC obviously showed a buffering effect against pH change.

• Journal of the Mineralogical Society of Korea
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• v.15 no.1
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• pp.1-10
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• 2002

The present study is focused on the granite weathering and soil formation, and the heavy metal contamination in soils in the Onsan industrial area. For profile study, soil sampling was conducted on each depth and experimental analyses have been conducted on those samples. X-ray diffraction analyses show that clay minerals consist mainly of kaolin minerals, vermiculite, and minor illite. Most of kaolin minerals in the lower kiwi of the profile consist of halloysite as confirmed by formamide intercalation, but the content of halloysite decreases gradually toward the surface since it has been transformed to kaolinite in the upper part of the profile. Thermal treatment by heating at $110^{\circ}C,\;300^{\circ}C,\;and\;550^{\circ}C$ shows a diffuse and broad peak the between 10 and $14\;{\AA}$ region in X-ray diffractograms. This suggests the possible existence of the hydroxy-Al interlayerecl vermiculite. Na-citrate extraction method reaconfirms this result showing transition of $14\;{\AA}$ peak to $10\;{\AA}$ In by removing the interlayer materials and restoring the vermiculite to its original state. The occurrence of hydroxy-Al interlayered vermiculite is also supported by soil pH distribution room 3.9 In the lower part to 3.6 in the upper part of the profile. Sequential extraction experiment was conducted to investigate the states of heavy metals in soils. The experiment shows that relatively high amounts of heavy metals are concentrated in the upper part of the profile and that most of them are bound to Fe/Mn oxides and organic matters while less concentration in clay minerals. The result indicates that most of heavy metal pollutants are concentrated in the surface soil and that the low concentrations of heavy metals in clays are mainly due to the low adsorption capacities of clay minerals such as kaolin minerals and hydroxy-Al interlayered vermiculite in acidified soil condition.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 1994.07a
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• pp.184-215
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• 1994

The Hydrogeologic data of 455 water wells comprising geologic and aquifer test were analyzed to determine hydrogeoloic characteristics of Cheju island. The groundwater of Cheju island is occurred in unconsolidated pyroclastic deposits interbedded in highly jointed basaltic and andesic rocks as high level, basal and parabasal types order unconfined condition. The average transmissivity and specific yield of the aquifer are at about 29,300m$^2$/day and 0.12 respectively. The total storage of groundwater is estimated about 44 billion cubic meters(m$^3$). Average annual precipitation is about 3390 million m$^3$ among which average recharge amount is estimated 1494 million m$^3$ equivalent 44.1% of annual precipitation with 638 million m$^3$ of runoff and 1256 million m$^3$ of evapotranspiration. Based on groundwater budget analysis, the sustainable yield is about 620 million m$^3$(41% of annual recharge)and rest of it is discharging into the sea. The geologic logs of recently drilled thermal water wens indicate that very low-permeable marine sediments(Sehwa-ri formation) composed of loosely cemented sandy sat derived from mainly volcanic ashes, at the 1st stage volcanic activity of the area was situated at the 120$\pm$68m below sea level. And also the other low-permeable sedimentary rock called Segipo-formation which is deemed younger than former marine sediment is occured at the area covering north-west and western part of Cheju at the $\pm$70m below sea level. If these impermeable beds are distributed as a basal formation of fresh water zone of Cheju, most of groundwater in Cheju will be para-basal type. These formations will be one of the most important hydrogeologic boundary and groundwater occurences in the area.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.1
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• pp.60-68
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• 2015

The study of waste activated sludge (WAS) solubilization has been increased for sludge volume reduction and enhancing the efficiency of anaerobic digestion. Microwave (MW)-assisted solubilization is an effective method for the solubilization of WAS because this method can lead to thermal, nonthermal effect and ionic conduction by dielectric heating. In this study, the solubilization of WAS by MW heating and conductive heating (CH) was compared and to enhance the MW-assisted solubilization of WAS at low MW output power, chemical agents were applied such as $H_2SO_4$ as the strong acid and $CaCl_2$, NaCl as the ionic materials. Compared to the COD solubilization of WAS by CH, that by MW heating was approximately 1.4, 6.2 times higher at $50^{\circ}C$, $100^{\circ}C$, respectively and the highest COD solubilization of WAS was 10.0% in this study of low MW output power condition. At the same MW output power and reaction time in chemically agents assisted experiments, the COD solubilization of WAS were increased up to 18.1% and 12.7% with the addition of $H_2SO_4$ and NaCl, however, that with the addition of $CaCl_2$ was 10.7%. This result might be due to the fact that the precipitation reaction occurred by calcium ion ($Ca^{2+}$) and phosphate ion (${PO_4}^{3-}$) produced in WAS after MW-assisted solubilization. In this study, $H_2SO_4$ turned out to be the optimal agent for the enhancement of MW efficiency, the addition of 0.2 M $H_2SO_4$ was the most effective condition for MW-assisted WAS solubilization.

• Journal of the Korean Magnetics Society
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• v.23 no.4
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• pp.122-125
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• 2013

Perpendicular magnetic anisotropy (PMA) is the phenomenon of magnetic thin film which is preferentially magnetized in a direction perpendicular to the film's plane. Amorphous multilayer with PMA has been studied as the good candidate to realization of high density STT-MRAM (Spin Transfer Torque-Magnetic Random Access Memory). The current issue of high density STT-MRAM is a decrease in the switching current of the device and an application of amorphous materials which are most suitable devices. The amorphous ferromagnetic material has low saturated magnetization, low coercivity and high thermal stability. In this study, we presented amorphous ferromagnetic multilayer that consists of an amorphous alloy CoSiB and a nonmagnetic material Pd. We investigated the change of PMA of the $[CoSiB\;t_{CoSiB}/Pd\;1.3nm]_5$ multilayer ($t_{CoSiB}$ = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 nm, and $t_{Pd}$ = 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 nm) and $[CoSiB\;0.3nm/Pd\;1.3nm]_n$ multilayer (n = 3, 5, 7, 9, 11, 13). This multilayer is measured by VSM (Vibrating Sample Magnetometer) and analyzed magnetic properties like a coercivity ($H_c$) and a magnetization ($M_s$). The coercivity in the $[CoSiB\;t_{CoSiB}\;nm/Pd\;1.3nm]_5$ multi-layers increased with increasing $t_{CoSiB}$ to reach a maximum at $t_{CoSiB}$ = 0.3 nm and then decreased for $t_{CoSiB}$ > 0.3 nm. The lowest saturated magnetization of $0.26emu/cm^3$ was obtained in the $[CoSiB\;0.3nm/Pd\;1.3nm]_3$ multilayer whereas the highest coercivity of 0.26 kOe was obtained in the $[CoSiB\;0.3nm/Pd\;1.3nm]_5$ mutilayer. Additional Pd layers did not contribute to the perpendicular magnetic anisotropy. The single domain structure evolved in to a striped multi-domain structure as the bilayer repetition number n was increased above 7 after which (n > 7) the hysteresis loops had a bow-tie shapes.

• Korean journal of applied entomology
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• v.51 no.4
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• pp.421-429
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• 2012

The developmental time period of Aphis gossypii was studied in laboratory (six constant temperatures from 15 to $30^{\circ}C$ with 50~60% RH, and a photoperiod of 14L:10D) and in a cucumber plastic house. The mortality of A. gossypii in the laboratory was high in the 2nd (20.0%) and 3rd stage(13.3%) at low temperature but high in the 3rd (26.7%) and 4th stage (33.3%) at high temperatures. Mortality in the plastic house was high in the 1st and 2nd stage but there was no mortality in the 4th stage at low temperature. The total developmental period was longest at $15^{\circ}C$ (12.2 days) in the laboratory and shortest at $28.5^{\circ}C$ (4.09 days) in the plastic house. The lower threshold temperature at the total nymphal stage was $6.8^{\circ}C$ in laboratory. The thermal constant required to reach the total nymphal stage was 111.1DD. The relationship between the developmental rate and temperature fit the nonlinear model of Logan-6 which has the lowest value for the Akaike information criterion(AIC) and Bayesian information criterion(BIC). The distribution of completion of each development stage was well described by the 3-parameter Weibull function ($r^2=0.89{\sim}0.96$). This model accurately described the predicted and observed outcomes. Thus it is considered that the model can be used for predicting the optimal spray time for Aphis gossypii.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.266-271
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• 2009

We designed a thermo-optic switch based on a directional coupler with not only a high extinction ratio but also significantly low power consumption. The switch operates by using the thermo-optic effect of the polymer which the refractive index changes by heating the electrode. If the electrode is not powered (OFF), the input light will be coupled completely to the other waveguide. When the electrode is powered at a certain level (ON), input light launched into the input waveguide will remain in that waveguide due to the lower index adjusted in the other waveguide. The switch based on the directional coupler was designed using the generalized extinction ratio curve and the lateral shift of the input waveguide. The coupling length is 1,610 ${\mu}m$ and the extinction ratios are -28 and -30 dB for ON and OFF states, respectively. The electrode structures were optimized by thermal analysis. The transported heat into the waveguide is increased, as the electrode width (w) is increased and the center distance between the electrode and the waveguide (d) is decreased. Also, because the heat generated in the electrode affects the other waveguide, the temperature difference between two waveguides is varied as the given w and d. There are specific conditions which have the maximum of the temperature difference. That of the temperature difference is increased as the width and the temperature of the electrode are increased. Especially, when the switch is designed using the condition with the maximum of the temperature difference for switching, the temperature of the electrode can be decreased. We expect this condition will be the novel method for the reduction of the power consumption in a thermo-optic switch.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.239-247
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• 2014

The (U-Th)/He dating utilizes the production of alpha particles ($^4He$ atoms) during natural radioactive decays of $^{238}U$, $^{235}U$ and $^{232}Th$. (U-Th)/He age can be determined from the abundances of the parent nuclides $^{238}U$, $^{235}U$ and $^{232}Th$ and the radiogenic $^4He$. Because helium is one of the noble gases (non-reactive) with a relatively small radius, it diffuses rapidly in many geological materials, even at low temperatures. Therefore, ingrowth of $^4He$ during radioactive decay competes with diffusive loss at elevated temperatures during the geologic time scale, determining the amount of $^4He$ existing today in natural samples. For example, He diffusion in apatite is known to be very rapid compared to that in most other minerals, causing a significant diffusive loss at ${\sim}80^{\circ}C$ or higher. At ${\sim}40^{\circ}C$, He diffusion in apatite becomes slow enough to preserve most $^4He$ in the sample. Thus, an apatite's (U-Th)/He age represents the timing when the sample passed through the temperature range of $80-40^{\circ}C$. The crustal depth corresponding to this temperature range is called a "partial retention zone." Normal closure temperatures for a typical grain size and cooling rate are ${\sim}60-70^{\circ}C$ for apatite and ${\sim}200^{\circ}C$ for zircon and titanite. Because the apatite He closure temperature is lower than that of most other thermochronometers, it can provide critical constraints on relatively recent or shallow-crustal exhumation histories.

• Journal of Bio-Environment Control
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• v.28 no.4
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• pp.420-428
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• 2019

This study is the heating energy saving test of the high-bed strawberry crown heating system. The system consists of electric hot water boiler, thermal storage tank, circulation pump, crown heating pipe(white low density polyethylene, diameter 16mm) and a temperature control panel. For crown heating, the hot water pipe was installed as close as possible to the crown part after planting the seedlings and the pipe position was fixed with a horticultural fixing pin. In the local heating type, hot water at $20{\sim}23^{\circ}C$ is stored in the themal tank by using an electric hot water boiler, and crown spot is partially heated at the setting temperature of $13{\sim}15^{\circ}C$ by turning on/off the circulation pump using a temperature sensor for controlling the hot water circulation pump which was installed at the very close to crown of strawberry. The treatment of test zone consisted of space heating $4^{\circ}C$ + crown heating(treatment 1), space heating $8^{\circ}C$(control), space heating $6^{\circ}C$ + crown heating(treatment 2). And strawberries were planted in the number of 980 for each treatment. The heating energy consumption was compared between November 8, 2017 and March 30, 2018. Accumulated power consumption is converted to integrated kerosene consumption. The converted kerosene consumption is 1,320L(100%) for space $8^{\circ}C$ heating, 928L(70.3%) for space $4^{\circ}C$ + crown heating, 1,161L($88^{\circ}C$) for space $6^{\circ}C$ + crown heating). It was analyzed that space $4^{\circ}C$ + pipe heating and space $6^{\circ}C$ + crown heating save heating energy of 29.7% and 12% respectively compared to $8^{\circ}C$ space heating(control).

• Journal of the Korean Institute of Gas
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• v.26 no.3
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• pp.45-53
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• 2022

In order to improve the emission of diesel engines, natural gas-diesel dual fuel combustion compression ignition engines are in the spotlight. In particular, a reactivity controlled compression ignition (RCCI) combustion strategy is investigated comprehensively due to its possibility to improve both efficiency and emissions. With advanced diesel direct injection timing earlier than TDC, it achieves spontaneous reaction with overall lean mixture from a homogeneous mixture in the entire cylinder area, reducing nitrogen oxides (NOx) and particulate matter (PM) and improving braking heat efficiency at the same time. However, there is a disadvantage in that the amount of incomplete combustion increases in a low load region with a relatively small amount of fuel-air. To solve this, sensitive control according to the diesel injection timing and fuel ratio is required. In this study, experiments were conducted to improve efficiency and exhaust emissions of the natural gas-diesel dual fuel engine at low load, and evaluate combustion stability according to the diesel injection timing at the operation point for power generation. A 6 L-class commercial diesel engine was used for the experiment which was conducted under a 50% load range (~50 kW) at 1,800 rpm. Two injectors with different spray patterns were applied to the experiment, and the fraction of natural gas and diesel injection timing were selected as main parameters. Based on the experimental results, it was confirmed that the brake thermal efficiency increased by up to 1.3%p in the modified injector with the narrow-angle injection added. In addition, the spray pattern of the modified injector was suitable for premixed combustion, increasing operable range in consideration of combustion instability, torque reduction, and emissions level under Tier-V level (0.4 g/kWh for NOx).