• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.25-32
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• 2002

The fractal dimension that was evaluated with soil components from the traditional particle-size distribution(PSD) curve was analyzed using the results of Wu et al.(1993) and Bittelli et al.(1999). In order to find the change of the variation of fractal dimension with the upper and lower limit, three limit values(200$\mu{m}$, 63$\mu{m}$, and 125$\mu{m}$) were chosen, and these results of fractal dimension analysis were compared to the result that was evaluated in the whole range of the soils. The results showed that it is possible to evaluate fractal dimension from the traditional PSD curve with the soil contents, and it showed that Bittelli et at.(1999)'s upper and lower limit value was more reasonable than Wu et al.(1993). Equations that were presented by Bittelli et at.(1999) also showed a good agreement with the analytical results in the silt domain.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.14 no.5
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• pp.362-369
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• 2001

The electrical properties of varistors consisting of Zn-Pr-Co-Cr-Er oxides were investigated in the Er$_2$O$_3$content range of 0.0 to 2.0 mol%. the varistors without Er$_2$O$_3$ exhibited a relatively low nonlinearity, which was 14.24 in the nonlinear exponent and 21.47 $\mu$A in the leakage current. However, the varistors with Er$_2$O$_3$ sintered at 1335$^{\circ}C$ for 1h exhibited very high nonlinear exponent of 70, in particular, reaching a maximum value of 78.05 in 2.0 mol% Er$_2$O$_3$, and those sintered at 1335$^{\circ}C$ for 2h exhibited the nonlinear exponent close to 50, in particular, reaching a maximum value of52.76 in 0.5 mol% Er$_2$O$_3$. The others except for 0.5 mol% Er$_2$O$_3$-added varistors exhibited very high instability resulting in a thermal runaway within a short time, even a weak DC stress. Increasing soaking time decreased the nonlinearity, but increased the stability. The varistors containing 0.5mol% Er$_2$O$_3$ sintered for 2h exhibited excellent stability, in which the variation rate of the varistor voltage and nonlinear exponent was -1.70% and -7.15%, respectively, under more severe DC stress such as (0.80 V$_{1mA}$/9$0^{\circ}C$/12h)+(0.85 V$_{1mA}$/115$^{\circ}C$/12h)+(0.90 V$_{1mA}$/12$0^{\circ}C$/12h)+(0.95 V$_{1mA}$/1$25^{\circ}C$/12h)+(0.95 V$_{1mA}$/15$0^{\circ}C$/12h).TEX>/12h).

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1003-1007
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• 1999

This paper is reported for the stability of ZnO-$Pr_{6}O_{11}-CoO-Er_{2}O_{3}$ based ceramic varistors with $Er_{2}O_{3}$ added in the addition range 0.0 to 2.0 mol%. The varistors sintered at $130^{\circ}C$ exhibited abrupt positive current creep phenomena, which accompany thermal run away within short times, even under weak d.c. stress. As a result, these varistors were completely degraded. On the contrary, the stability of varistors sintered at $1350^{\circ}C$ was far better than that of $1300^{\circ}C$. In particular, the varistor containing 0.5 mol% $Er_{2}O_{3}$ showed a excellent stability, which the variation rate of the varistor voltage, the nonlinear coefficient, and leakage current is below 1%, 2%, and 3.5%, respectively, even under more severe d.c. stress, such as ($0.8V_{1mA}/90^{\circ}C/12h$) + ($0.85V_{1mA}/115^{\circ}C/12h$) + ($0.9V_{1mA}/120^{\circ}C/12h$) + ($0.9V_{1mA}/150^{\circ}C/12h$). Consequently, it is estimated that the basic composition of ZnO-$Pr_{6}O_{11}-CoO-Er_{2}O_{3}$ based varistor contain 0.5 mol% $Er_{2}O_{3}$ will be used to the fabrication of the varistors for high performance and stability in a forthcoming.

• Journal of the Mineralogical Society of Korea
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• v.9 no.2
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• pp.55-63
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• 1996

Epidote occurs as veinlets in the propylitic alteration zone of the Bobae clay deposit, Pusan, Korea. Its cell parameters apparently decrease with the contents of Al, Fe, and Ca. Fourier transform infrared (FTIR) spectra show one hydrosyl environment related to AlM2 at 3357-3358 cm-1. In the mid-infrared region, the peaks at 950 and 1030 cm-1 sharper with increasing Al shifting to higher energy region. The peak at 885 cm-1 shifts slightly to a lower energy region with a decreasing intensity as the Fe content increases. In the far-IR region, epidote exhibits absorption bands at 120 and 140 cm-1, which are related to the Ca-O bonds in A-sites.M ssbauer spectra of epidote show that the isomer shifts of Fe3+ range from 0.36-0.37 at the M3 site and from 0.35-0.44 at M1 site. Fe2+ shows the isomer shift ranging from 1.11 to 1.13. Quadrupole splitting is 2.04 for Fe3+M3, 0.52-0.70 for Fe3+M1, and 2.61-2.70 for Fe2+M3. Calculation shows Fe3+M386-90.7%, Fe3+M12.5-3.6%, and Fe2+M35.8-11.4% of total iron, showing preferential distribution of Fe3+ in the M3 site. The Fe3+M3 content is between 0.486 and 0.513 per formula unit. in the Fe-rich epidote, less Fe3+ and more Fe2+ are accommodated in the M1 and M3 sites. Hence, the overall disorder increases as total Fe content increase. The ordering parameter of the Bobae epidote is 0.93-0.95, suggesting a disequilibrium state below 200$^{\circ}C$. The constant temperature over a long period may be essential for the transition from disordered state to equilibrium state, despite the possible variation in flux and composition of the hydrothermal fluid.

• Journal of Applied Biological Chemistry
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• v.59 no.4
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• pp.361-364
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• 2016

We developed a spectrophotometric assay method for polyethoxylated ascorbic acidusing 3-ethyl ascorbic acid as standard material. The analytical method was validated by linearity, accuracy, precision, and stability. The coefficient of variation of the precision of the assay was less than 3.4 %. The linearity of the calibration curves in the desired concentration range is good ($r^2$>0.998). 3-Ethyl ascorbic acid and polyethoxylated ascorbic acid were stable in stock solution at room temperature for up to at least 6 h. The developed assay could be used for the content analysis of polyethoxylated ascorbic acid in samples.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.8
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• pp.1963-1970
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• 1998

In this paper, a two-dimensional slotline coupling structure is proposed for the planar active phased array antenna system with scanning the beam by coupled oscillators without phase shifters. The operating characteristics are analyzed and experimentally demonstrated. The proposed two-dimensional slotline coupling structure consists of $|{=}|$-type slotline in the ground plane for the coupling of E-plane and H-plane. From the simulation results of coupling strength with the variation of width, length and the number of slotlines, the optimal coupling structure is proposed and applied to $2{\times}5$ elements of planear phased array antenna. The experimental results show that the beamwidth of E-plane and H-pland are $42^{\circ}$ and $15^{\circ}$, respectivly, and the scanning range is from $-20^{\circ}$ to $15^{\circ}$ from the broadside. Therefore, it is shown the two-dimensional slotline coupling structure for oscillator-type active phased array antenna can be applied to the planar phased array antenna system.

• 한국전산유체공학회:학술대회논문집
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• 2002.10a
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• pp.133-138
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• 2002

A 3-D axisymmetric computer program is developed to predict the NO behavior in SNCR system for the stoker incinerator with the waste treatment capacity, 200ton/day. To this end a turbulent reacting flow field calculation is made using proper assumption and empiricism. The stoker bed is assumed to be a homogeneous waste-volatilized gaseous state. The initial composition or reactants are assumed based on the data of the ultimate analysis. Turbulent is resolved by k-e model and turbulent reaction is handled by eddy-breakup model harmonized with empirical chemistry data for gaseous combustion, NO and urea reaction. The liquid droplet is traced by Lagrangian method incorporated by aerodynamic drag, Coriolis and crntrifugal forces. Radiation is treated by sensible heat loss model. Calculation results are in good agreement with experimental data at the outlet of post combustion chamber in Daejon 4th industrial complex. The flue gas shows the temperature range of $900\sim1000^{\circ}C$, velocity of 5m/s and NO concentration of 140ppm at the exit while the measured temperature, flue gas velocity and NO concentration are $967^{\circ}C$, $3\sim4m/s$ and $100\sim200ppm$respectively. Using the developed computer program a parametric study has been made with the variation of heat content of waste, castable length and SNCR variables for the determination of proper injector location. In general, the calculated results are consistent and physically acceptable.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4
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• pp.32-35
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• 1996

The pressure pulses generated from the underwater electric spark system ranged from 0.4 to 1.6kJ are measured with the variation of source depth and range. The characteristics of pressure pulses obtained through this experiment continue to show the same electric energy and depth dependence previously reported, but two particular phenomena are observed. First, it is observed that the peak pressure of the 1st bubble pulse induced from implosion is higher than that of the initial shock wave, which is particularily apparent to high electric energy more than 10kJ previous studies. Second, it has been reported that the energy ratio (potential energy of bubble/intrinsic energy of source) has some tendency to "droop" on the low electric energy as 0.02 for 5kJ and 0.01 for 1kJ but the results of the present experiment show that it continues to have the ratio of 0.01 near 1kJ again.

• Journal of the Korean Solar Energy Society
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• v.23 no.2
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• pp.71-79
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• 2003

The goal of this paper is to measure and compare the performance of solar heat pump for refrigerants. To accomplish the goal, solar heat pump with aluminum roll bond type evaporator and indoor heat exchanged(condenser) was built. The test results showed that the COP and heating capacity of HFC-32/125/134a(23/25/52 wt%, $CH_2F_2/CF_3CHF_2/CF_3CH_2F$) were higher than those of HCFC-22$(CHClF_2)$. A study proved that best conditions to use heating system that is about $40m^2$ and $80m^2$. The COP range of the whole system was from 4 to 6 according to the solar collector's area variation. Hydrochlo-rofluorocarbon HCFC-22$(CHClF_2)$ is included in the compound to be controlled. HFC-32/125/134a(23/25/52 wt%, $CH_2F_2/CF_3CHF_2/CF_3CH_2F$) is the most suitable replacement HCFC-22$(CHClF_2)$ in solar heat pump application. The solar heat pump system was designed to show the best efficiency that the room temperature make $18\sim20^{\circ}C$ and $23\sim25^{\circ}C$ in Seoul during the fall season.

• Journal of the Korean Institute of Landscape Architecture
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• v.31 no.1
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• pp.66-77
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• 2003

The purpose of this study is to propose a standard putting green management program to prepare fast green suitable for international golf tournaments, and to conform whether the reported green speed model can be applied to the real field situations. The west course of Lakeside Country Club was selected for the case study. This study was initiated on August 1st, 2001 and continued through October 4th, 2001. The results are summarized as follows: 1. Following the long-term schedule, 'penncross' creeping bentgrass turf was mowed at 5.0mm(37days), 4.5mm(8days), 4.0mm(4days), 3.5mm(2days), 3.2mm(2days), 3.0mm(2days), 2.8mm(2days) and the mowing direction was changed daily. Variation of mowing height was reduced to a minimum range. Core aerification with deep tines was applied 19 days prior to the first practice round. Dry sand maintenance was top-dressed 2 times at 1.5mm/$m^2$ on the 17th day and 1.0mm/$m^2$ on the 10th day. Minimum irrigation was applied to keep the turf alive. During the tournament preparation week, dew on the putting greens was removed by using a sponge roller. Following the dew removal, the greens were cut once each morning at a height of 2.8mm. The mower used was the 21 inch working behind mower equipped with a tournament bedknife and 11 reel blades. Following the mowing, the peens were rolled with a light-weight roller in one direction in the morning. Rolling was used as a finishing technique to ensure that the surface was as smooth as possible, and to provide true ball roll and maximum green speed. In conclusion these management practices satisfied the daily green stimpmeter readings required for USGA championship play. 2. During the period of tournament preparation, no damage was observed on the green, but scalping in green edge appeared in about 0.39% of the total area of 18 greens in the west course.