• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.167-174
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• 2003

Fatigue damage of 2.2Ni-1Cr-0.5Mo steel used fir high strength pressure tubes and vessels was evaluated using uniaxial specimens subjected to strain-controlled fatigue loading. Based on the fatigue test results from different strain ratios of -2. -i 0, 0.5, 0.75, the fatigue damage of the steel was represented by using a cyclic strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Compared to other fatigue damage parameters, fatigue life prediction by the cyclic strain energy density showed a good correlation with the experimental fatigue lift within a factor of 3.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.4
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• pp.67-74
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• 2004

As data rate was increased, the conventional burst-mode automatic power control circuit caused errors due to the effort of the mark density variation. To solve this problem we invented a new structured peak-comparator which could eliminate the effect of the mark density variation even in high date rate, and revised the conventional one using it. We proposed a burst-mode automatic power control circuit robust to mark density variations. We found that the peak-comparator in the proposed automatic power control circuit was very robust to mark density variations because it affected very little by the mark density variation in high date rate and in the wide variation range of the reference current and the difference current.

• Journal of Environmental Health Sciences
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• v.22 no.3
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• pp.49-55
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• 1996

Water parsley(Oenanthe javanica(Blume) DC) was raised with varying population density(S) in the laboratory aquarium unit to determine the growth equation. The population density was measure after 7 days. The resultant growth curve was well fit to the equation 1/S = A+B (1/S0) with a high correlation coefficient ($R^2$ = 0.999). The maximum specific absorption rate was $9.011 \times 10^{-5}$ kg $NO_x-N/kg$ water parsley$\cdot$day and $1.31 \times 10^{-5}$ kg $PO_4-P/kg$ water parsley$\cdot$day when the average population density was $2.62 kg/m^2$. The relationship between population density and nutrient absorption rate, the absorption rate of $NO_x-N$ was 5.04~5.24 mg/l$\cdot$day when the population density was $7.51~10.0 $mg/m^2\cdot day$ and the absorption rate of $PO_4-P$ was 0.56~0.78 mg/l$\cdot$day when the population density was 5.02~10.0 $kg/m^2\cdot day$. Taking into account the nutrient absorption rate and growth rate, the population density between $7.0 kg/m^2\cdot day$ and $8.0 kg/m^2 \cdot day$ was selected. The removal rate of nutrient was investigated after 7 days culture. Removal rate of $NO_x-N$ was 95.6~99.95% with initial concentration of 35 mg $NO_x-N/l$, and the removal rate of $PO_4-P$ was also high, indicating 80.24~98.9% with initial concentration of 5.95 mg $PO_x-P/l$.

• Transactions of the Society of Information Storage Systems
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• v.3 no.2
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• pp.94-112
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• 2007

Nano-sized inverted domain dots in ferroelectric materials have potential application in ultrahigh-density rewritable data storage systems. Herein, a data storage system is presented based on scanning non-linear dielectric microscopy and a thin film of ferroelectric single-crystal lithium tantalite. Through domain engineering, we succeeded to form an smallest artificial nano-domain single dot of 5.1 nm in diameter and artificial nano-domain dot-array with a memory density of 10.1 Tbit/$inch^2$ and a bit spacing of 8.0 nm, representing the highest memory density for rewritable data storage reported to date. Sub-nanosecond (500psec) domain switching speed also has been achieved. Next, long term retention characteristic of data with inverted domain dots is investigated by conducting heat treatment test. Obtained life time of inverted dot with the radius of 50nm was 16.9 years at $80^{\circ}C$. Finally, actual information storage with low bit error and high memory density was performed. A bit error ratio of less than $1\times10^{-4}$ was achieved at an areal density of 258 Gbit/inch2. Moreover, actual information storage is demonstrated at a density of 1 Tbit/$inch^2$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.799-800
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• 2006

Wrought Si-steels are generally used for electromagnetic valves, which are needed good response. To date, Hitachi Powdered Metals Co., Ltd. have produced Fe-Si base sintered magnetic material, EU-52, which shows a magnetic flux density of more than 1.25T at 2000A/m and a maximum permeability of more than 3500. However these magnetic properties are lower than that of wrought Si-steels. Because EU-52 has a low density of $7.2Mg/m^3$. For improving the magnetic properties, it is necessary to increase the density of sintered cores. To increase density, a new mixing method of coating fine Si powders on atomized iron powders was developed, for avoiding the Kirkendall effect. As the result, developed P/M Fe-Si magnetic cores shows higher density of $7.38Mg/m^3$, higher magnetic flux density of 1.48T at 2000A/m and higher maximum permeability of 6800.

• Journal of Magnetics
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• v.22 no.2
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• pp.203-213
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• 2017

Magnetically suspended control & sensitive gyroscope (MSCSG) is a novel type of gyroscope with the integration of attitude control and attitude angular measurement. To improve the precision and reduce the power consumption of Lorentz Force-type Magnetic Bearing (LFMB), the air gap flux density distribution of LFMB has been studied. The uniformity of air gap flux density is defined to qualify the uniform degree of the air gap flux density distribution. Considering the consumption, the average value of flux density is defined as well. Some optimal designs and analyses of LFMB are carried out by finite element simulation. The strength of the permanent magnet is taken into consideration during the machining process. To verify the design and simulation, a high-precision instrument is employed to measure the 3-dimensional magnetic flux density of LFMB. After measurement and calculation, the uniform degree of magnetic flux density distribution reaches 0.978 and the average value of the flux density is 0.482T. Experimental results show that the optimal design is effective and some useful advice can be obtained for further research.

• Elastomers and Composites
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• v.50 no.3
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• pp.196-204
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• 2015

Crosslink density of a rubber vulcanizate determines the chemical and physical properties, while bound rubber is an important factor to estimate reinforcement of a filled rubber compound. Extender oil is added to a raw rubber with very high molecular weight for improving processability of a rubber composite. Influence of extender oil on crosslink density, bound rubber formation, and physical properties of solution styrene-butadiene rubber (SSBR) composites with differing microstructures was investigated. Crosslink densities of non-oil-extended SSBR (NO-SSBR) vulcanizates were higher than those of oil-extended SSBR (OE-SSBR) ones. Bound rubber contents of NO-SSBR compounds were also greater than those of OE-SSBR ones. The experimental results could be explained by interfering of extender oil. The OE-SSBR vulcanizates had low modulus but long elongation at break, whereas the NO-SSBR ones had high modulus but short elongation at break. It was found that the crosslink densities affected the physical properties more than the bound rubber contents. The moduli increased with increase in the crosslink density irrespective of extender oil, while the elongation at break decreased. Each variation of the tensile strengths of NO-SSBR and OE-SSBR vulcanizates with the crosslink density showed a decreasing trend. Tear strength of the OE-SSBR vulcanizate increased with increase in the crosslink density, whereas variation of the tear strength of NO-SSBR vulcanizate with the crosslink density showed a weak decreasing trend.

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.47-54
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• 2010

The SuperCritical Water-cooled Reactor (SCWR) pursues high power density to reduce its capital cost. The fast spectrum SCWR, called a super fast reactor, can be designed with a higher power density than thermal spectrum SCWR. The mechanism of increasing the average power density of the super fast reactor is studied theoretically and numerically. Some key parameters affecting the average power density, including fuel pin outer diameter, fuel pitch, power peaking factor, and the fraction of seed assemblies, are analyzed and optimized to achieve a more compact core. Based on those sensitivity analyses, a compact super fast reactor is successfully designed with an average power density of 294.8 W/$cm^3$. The core characteristics are analyzed by using three-dimensional neutronics/thermal-hydraulics coupling method. Numerical results show that all of the design criteria and goals are satisfied.

• Journal of Korea Foundry Society
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• v.42 no.6
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• pp.392-397
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• 2022

In order to compliant the stringent exhaust emission regulations, higher fuel efficiency and cleaner exhaust gas in combustion engines have been required. To improve combustion efficiency, an exhaust gas temperature is increasing, therefore higher temperature resistance is required for components in exhaust system, especially turbine wheel in turbocharger. IN100 looks quite attractive candidate as it has high temperature properties with low density, however it has low castability due to poor ductility at high temperature. In this study, the balance of Al and Ti composition was optimized from the base alloy IN100 to improve the high temperature ductility by expanding the γ single phase region below the solidification temperature, while obtaining the high temperature strength by maintaining the volume fraction of γ' phase equivalent to IN100 around 1000℃. Furthermore, the high temperature creep rupture life increased by adding a small amount of Ta. The alloy developed in this study has high castability, low density and high specific strength at high temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.142-142
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• 2011

Microwave diagnostics method for plasma science and engineering is vigorous research area for its good characteristics such as high sensitivity, reliability, and broad measurement spectrum from low density plasma to high density. We investigate mechanism of microwave probes (hairpin, impedance and absorbtionf probe) and apply it for interpretation of full transmitted spectrum of cutoff probe. Mechanism of the spectrum having same key roles of I-V curve of Langmuir probe is not exactly revealed yet in spite of its importance. This study elucidates physics behind it using a circuit model and E/M wave simulation. Circuit model reveals exact cut-off peak frequency taking account of a collision frequency and a plasma frequency and it enable precise diagnostics of plasma densty from low pressure to high pressre. Cut-off like peaks have been obstacle for choosing cut-off peak is analyzed by E/M simulation and one of cutoff like peaks made by probe holder used for acquire plasma density with cutoff peak applying the hairpin relation. Furthermore, phase difference method for plasma density is conducted. This method uses a single microwave frequency source and it is low-priced.