• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.199-204
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• 2010

The objective of this paper is to present new binder systems that can be applied in composite rocket propellants, to improve properties of these propellants not only for better performance, but also to reduce waste and pollution. These novel systems are based on the thermoplastic elastomer (TPE) binders, which consists of copolymers with the addition of a plasticizer, and additives. The effect of the novel TPE binder systems on the burning rate and mechanical properties of AP based propellants was studied. The results show that propellants based on the novel TPE binders have a better energy performance than today's workhorse hydroxyl terminated polybutadine/ammonium perchlorate propellant, exhibit a similar range of burning rate, possess appropriate mechanical properties, and exhibit good processing and aging characteristics at low cost.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.623-624
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• 2006

The behavior of hardmetals under cyclic loads is investigated. Unnotched specimens were employed to obtain practical information regarding fatigue in hardmetals. All the tested hardmetals exhibit an increase in the number of cycles until failure with a decrease in the maximum stress, i.e., the hardmetals exhibit a high fatigue sensitivity. The fatigue strength increases with the cobalt content. Although distinct fatigue limits, as observed in metals, cannot be observed, the calculated fatigue limit stress at $10^7$ cycles is found to be approximately 70% of the flexural strength, and the stress value exhibits a linear relationship with the flexural stress.

• Journal of Biosystems Engineering
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• v.27 no.2
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• pp.107-116
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• 2002

This study was designed to analyze farmers' behavior on dealing with secondhand agricultural machinery and to device proper measures for promoting utilization of secondhand agricultural machinery. This objective was accomplished by using data which were analyzed, collected through questionnaires from 35 farmers on dealing with secondhand agricultural machinery. The main, realistic measures for promoting utilization of secondhand agricultural machinery, based on farmers' behavior, are as fellows: First, to make and offer a criteria fer evaluating the optimal price of secondhand agricultural machinery, which should be a effective measure for promoting farmers' dealing with them. Second. to establish a store to exhibit and sell secondhand agricultural machinery. This is the most important way to promote dealing with them. In the process of political supporting to establish the store, the equality of opportunity should be adopted to every organization want to deal secondhand agricultural machinery. Third, to strengthen financial supports for buying secondhand agricultural machinery and to assure A/S system.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.101-108
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• 2003

Polymeric positive temperature coefficient(PTC) composites have been prepared by incorporating carbon black(CB) into high density polyethylene(HDPE), polyphenylene sulfide(PPS) and polybutylene terephthalate(PBT) matrices. A PTC effect was observed in the composite, caused by the large thermal expansion due to He consecutive melting of HDPE, PPS and PBT crystallites. This theory is based upon the premise that the PTC phenomenon is due to a critical separation distance between carbon particles in the polymer matrix at the higher temperature. The influence of PTC characteristics of the PPS/CB composite can be explained by DSC result. HDPE, one of prepared composition, exhibit the higher performance PTC behavior that decreaseing of negative temperature coefficient(NTC) effect and improved reproducibility by chemically crosslinking. Also, PBT/CB and PPS/CB composites exhibit the higher PTC peack temperature than HDPE/CB PTC composite, individually $200^{\circ}C$ and $230^{\circ}C$. These PTC composite put to good use in a number of safety application, such as self$.$controlled heater, over-current protectors, auto resettable switch, high temperature proctection sensor, etc.

• Journal of Technology Innovation
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• v.7 no.1
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• pp.124-150
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• 1999

This study examines the personal characteristics, organizational attitudes, technical performances, and reward preferences of R&D professionals with Ph.D. degree in large private companies in Korea. Based on survey data from 887 professionals in nine different R&D organizations, the following results are found; 1) R&D professionals with Ph.D. degree exhibit higher autonomy preference, need for achievement, self-efficacy, technical career orientation, and performance proficiency than other R&D professionals; 2) As their organizational tenure increases, performance proficiency and transfer career orientation increases but their socialized level of organizational goals and values does not change; 3) They produce more technical publications and exhibit more positive organizational attitude than other R&D professionals; 4) They are more likely to prefer job content, professional, and job security rewards. These empirical findings suggest several theoretical and practical implications for the management of R&D professionals with Ph.D. degree in the large Korean firms.

• Archives of Pharmacal Research
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• v.18 no.2
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• pp.65-68
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• 1995

The methanol extract from the whole parts of the flowers of Chrysanthemum boreals was found to exhibit a significant inhibition of a rat lens aldose reductase (RLAR) activity in vitro. Bioassay guided systematic fractionation of the methanol extract led to the isolation of four flavonoids which were identified as acacetin (1), apigenin (II), luteolin (III) and linarin (IV). Compounds I-III were demonstrated to exhibit a significant inhibition of RLAR. Luteolin (II) was found to be the most potent AR inhibitor with $IC_{50}$ value of $5{\times}10^{-7}M$.

• Journal of the Korean Chemical Society
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• v.63 no.4
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• pp.237-245
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• 2019

Hydrogen bihalide anions, $XHX^-$ (X = F, Cl, and Br) have been studied by high level ab initio methods to determine the molecular structure, vibrational frequencies, and energetics of the anions. All bihalide anions are found to be of linear and symmetric structures, and the calculated bond lengths are consistent with experimental data. The harmonic frequencies exhibit large deviations from the experimental frequencies, suggesting the vibrations of these anions are very anharmonic. Two different approaches, the VSCF and VPT2 methods, are employed to calculate the anharmonic frequencies, and the results are compared with the experimental frequencies. While the ${\nu}_1$ and ${\nu}_2$ frequencies are in reasonable agreement with the experimental values, the ${\nu}_3$ and ${\nu}_1+{\nu}_3$ frequencies still exhibit large deviations. The hydrogen-bond energies and enthalpies are calculated at various levels including the W1BD and G4 composite methods. The hydrogen-bond enthalpies calculated are in good agreement with the experimental values.

• Communications of the Korean Mathematical Society
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• v.11 no.1
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• pp.147-151
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• 1996

In this paper we consider n-species autonomous competitive Lotka-Volterra systems. We exhibit here simple algebraic criteria on the parameters which guarantee the coexistence of all the species.

• Bulletin of the Korean Mathematical Society
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• v.35 no.3
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• pp.465-471
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• 1998

The class of finite solube groups with zero deficiency known to have soluble lenght five or six is small. In this paper we exhibit some classes of such goups.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.230.2-230.2
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• 2015

Nanoparticles of magnesium ferrite are used as a heterogeneous catalyst, humidity sensor, oxygen sensor and cure of local hyperthermia. These applications usually utilize the magnetic behavior of these nanoparticles. Moreover, magnetic properties of nanoferrites exhibit rather complex behavior compared to bulk ferrite. The magnetic properties of ferrites are complicated by spins at vortices, surface spins. Reports till date indicate strong dependency on the structural parameters, oxidation state of metal ions and their presence in octahedral and tetrahedral environment. Thus we have carried out investigation on magnesium ferrite nanoparticles in order to study coordination, oxidation state and structural distortion. For present work, magnesium ferrite nanoparticles were synthesized using nitrates of metal ions and citric acid. Fe L-edge spectra measured for these nanoparticles shows attributes of $Fe^{3+}$ in high spin state. Moreover O K-edge spectra for these nanoparticles exhibit spectral features that arises due to unoccupied states of O 2p character hybridized with metal ions. Mg K-edge spectra shows spectral features at 1304, 1307, 1311 and 1324 eV for nanoparticles obtained after annealing at 400, 500, 600, 800, 1000, and $1200^{\circ}C$. Apart from this, spectra for precursor and nanoparticles obtained at $300^{\circ}C$ exhibit a broad peak centered around 1305 eV. A shoulde rlike structure is present at 1301 eV in spectra for precursor. This feature does not appear after annealing. After annealing a small kink appear at ~1297 eV in Mg K-edge spectra for all nanoparticles. This indicates changes in local electronic structure during annealing of precursor. Observed behavior of change in local electronic structure will be discussed on the basis of existing theories.