• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.11
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• pp.1161-1170
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• 2009

In this paper, dielectric, drude model and ideal metamaterial are applied to core of A-Sandwich radome and each radome is analyzed using recursive method in Ku band. The main parameters of radome performance are insertion loss, insertion phase delay and depolarization. In case of ideal metamaterial, the radome using ideal metamaterial dose not generate depolarization because insertion loss, insertion phase delay and loss for incidence angle of wave do not happened. If circular polarization wave is incident on radome with meta material, transmitted wave also keeps circular polarization. In case of the dispersive metamaterial, the performance of radome using dispersive metamaterial is better than it of radome using dielectric in a part of frequency band. From these results, it is showed that metamaterial can be applied to various radome structure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.6
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• pp.551-561
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• 2009

FH system is very robust to the jamming interference. OFDM system is very good for the high speed communication system. But, it has high PAPR. SC-FDMA system based on OFT-spread OFDM was proposed to reduce high PAPR. Therefore, in this paper, we like to introduce the FH system into SC-FDMA system, which can be best solution to the jamming hostile environment and for the high power efficiency. Also, OFDM is very sensitive to ICI. Especially, ICI generated by frequency offset and phase noise breaks the orthogonality among sub-carriers, which seriously degrades the system performance. We analyze the performance of the FH SC-FDMA system in the PBJ and MTJ channel. In this paper, the ICI effects caused by phase noise, frequency offset and Doppler effects are analyzed and we like to propose the PNFS algorithm in the equalizer to compensate the ICI influences. Through the computer simulations, we can confirm the performance improvement.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.529-538
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• 2002

There is no adverse opinion on the anticariogenic effect of fluoride, so glass ionomer restoration which release the fluoride is recommended fer child patient. To study the anticariogenic effect of initial carious lesion of fluoride released from adjacent glass ionomer restoration, the in situ model was constructed. A microhardness test, polarized scope investigation and electron probe microanalysis was done for analyzing the distribution of fluoride which was precipitated from glass ionomer restoration to the enamel caries lesion. Fuji IX, the conventional glass ionomer, was used for experimental group and Z-100, composite resin that fluoride was not contained, was used for control group. On the microhardness test, the remineralization was accelerated by fluoride. And on the polarized investigation, the size of caries lesion was reduced in the oral cavity and that phenomenon was accelerated by fluoride, too. Electron probe microanalysis shows that the remineralization was accelerated by fluoride and the fluoride concentration on subsurface area was increased. It maybe that the subsurface area was critical to anticariogenic effect. In summary of these result, initial caries lesion can be remineralized in the oral cavity and that phenomenon can be accelerated by fluoride. The subsurface area of caries lesion was a major part of defense to cariogenic invasion and to conserve the subsurface area, the surface of lesion body have to conserved.

• Composites Research
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• v.29 no.3
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• pp.117-124
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• 2016

The failure strength of composite single-lap joint repaired using scarf patch was investigated by test and finite element method. A total of 45 specimens were tested changing scarf ratio, stacking pattern, and defect size to study the failure strength and mode. Except for one case, all repaired specimens showed the equal or higher strength than the sound specimens and the effect of considered repair parameters was not remarkable. It was found through the failure mode inspection that the surface treatment for bonding was not enough in the case which failed at the lower load than the sound specimen. Three-dimensional finite element analysis was conducted to verify the test results. It was confirmed that the considered repair parameters do not significantly affect the stress distribution of the specimens. It was also observed that the applied tensile load is relieved passing through the overlapped region thickness of which is almost double. From this study, it is concluded that if the bonding procedure for adherends and patch including surface treatment for fabric layer is thoroughly followed, the strength of repaired single-lap joint can be restored up to the strength of sound one.

• The Journal of Industrial Distribution & Business
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• v.9 no.7
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• pp.61-70
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• 2018

Purpose - The purpose of this research is reflected on the rapid development of online tourism industries. The study was to establish the strategy for Korean tourism enterprises to develop tourist commodities suitable for Chinese tourists and attract them to visit Korea by the empirical analysis of the relation between repurchase intention of tourists and its premise variables (e-service quality, perceived value and satisfaction). Research design, data, and methodology - This research carried out a questionnaire survey on Chinese tourists who visited Korea with experience of using the online travel agency web sites. A total 398 answers were recovered, 41 of them were excluded due to the dishonest answers and 357 of them were finally analyzed. The data was analyzed with IBM SPSS AMOS 22.0. Results - The research results show that in the online travel agency web site e-service quality, convenience, interactivity, information validity, credibility had a positive impacts on perceived value and satisfaction. The perceived value of online travel agency website users has positive impart on satisfaction and repurchase intention. Satisfaction of online travel agency web site users have positive impacts on repurchase intention. But safety has no impact on perceived value while positive impacts on satisfaction was affected. Conclusions - First, in the online travel agency web site e-service quality, safety has no impact on perceived value while it was shown to have positive impacts on satisfaction because the users of online travel agency web sites believe that the protection of personal information, the defense of cracker and the safeguard of payment security are the basic premises of website operation. Although safety does not have impacts on perceived value, users benefits will suffer damage when hacker intrusion and other accidents occur so that online travel agency web sites should not ignore the security concerns. Second, credibility is a major concern for online travel agency web site users. At this time, it is necessary for the web site to establish a system to display both the commodity information and the using experience published on the user's SNS, thus improving the credibility of the website information.

• Biomedical Science Letters
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• v.11 no.2
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• pp.165-173
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• 2005

A potent demethylating agent, 5-Azacytidine (5-AzaC) has been widely used as in many studies on DNA methylation, regulation of gene expression, and cancer biology. The mechanisms of the demethylating activity were known to be formation of complex between DNA and DNA methyltransferase (MTase), which depletes cellular MTase activity. However, 5-AzaC can also induce hypermethylation of a transgene in a transgenic cell line, G12 cells and it was explained as a result of defense mechanisms to inactivate foreign gene(s) somehow. This finding evoked the question that whether the phenomenon of hypermethylation induced by 5-AzaC is limited to the transgene or it can be occurred in endogenous gene(s). In order to answer the question, mutagenicity test of 5-AzaC and molecular characterization of mutants obtained from the test were performed using an endogenous gene, thymidine kinase (tk) in Chinese hamster V79 cells. When V79 and V79-J3 subclone cells were treated with 1, 2.5 ,5, $10{\mu}M$ of 5-AzaC for 48 hours, their maximum mutant frequencies were revealed as $6\times10^{-3}\;at\;5{\mu}M$(350-fold induction over background) and $8\times10^{-3}\;at\;2.5{\mu}M$ (l,800-fold induction over background) respectively. Since the induction rates were too high to be induced by true mutations, many trifluorothymidine (TFT)-resistant $(TFT^R)$ cells were subjected to Northern blot analysis to check the presence of tk transcripts. Surprisingly, all clones tested possessed the transcripts in a similar level, that implicates the $TFT^R$ phenotype induced by 5-AzaC has not given rise to hypermethylation of the gene in spite of unusually high mutation frequency. In addition, it has shown that the TK activity in the pool of 5-AzaC-induced $TFT^R$ cells has about a half of that in spontaneously-induced $TFT^R$ cells or in non-selected parental V79-J3 cells. This result suggests that the mechanism(s) underlying the TFT-resistance between spontaneously occurred and 5-AzaC-induced cells may be different. These findings have shown that the $TFT^R$ phenotype induced by 5-AzaC has not given rise to hypermethylation of the tk gene, and 5-AzaC may be induced by one or combined pathways among many drug resistance mechanisms. The exact mechanisms for the 5-AzaC-induced $TFT^R$ phenotype remain to elucidate.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.27 no.2
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• pp.281-292
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• 2017

It is demanded to promote research and development of cyber weapons system and core technology in response to the ongoing cyber attack of North Korea. In this paper, core technologies of the future cyber weapon system are developed and the factors affecting the realization timing of core technologies were analyzed. 9 core technology groups and 36 core technologies are derived. Afterwards, these core technology groups are compared to the operation phase of the joint cyber warfare guideline and the cyber kill chain of Lockheed Martin. As a result of the comparison, it is confirmed that the core technology groups cover all phases of the aforementioned tactics. The results of regression analyses performed on the degree of influence by each factor regarding the moment of core technology realization show that the moment of core technology realization approaches more quickly as factors such as technology level of the most advanced country, technology level of South Korea, technology transfer possibility from the military sector to the non-military sector(spin-off factor), and technology transfer possibility from the non-military sector to the military sector(spin-on factor) increase. On the contrary, the moment of core technology realization is delayed as the degree at which the advanced countries keep their core technologies from transferring decrease. The results also confirm that the moment of core technology realization is not significantly correlated to the economic ripple effect factor. This study is meaningful in that it extract core technologies of cyber weapon system in accordance with revision of force development directive and join cyber warfare guideline, which incorporated cyber weapon system into formal weapon system. Furthermore, the study is significant because it indicates the influential factor of the moment of core technology realization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.5
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• pp.555-564
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• 2016

This paper proposes a time slot allocation scheme for military patrol environments. This proposal comes from analysis of traffic properties in a military patrol environment. In the near future, robots are expected to explore enemy grounds and measure threat, taking the place of human patrol. In order to control such robots, control messages must be extremely accurate. One mistake from the control center could cause a tragedy. Thus, high reliability must be guaranteed. Another goal is to maintain a continual flow of multimedia data sent from patrol robots. That is, QoS (Quality of Service) must be guaranteed. In order to transmit data while fulfilling both attributes, the per-path based centralized TDMA slot allocation scheme is recommended. The control center allocates slots to robots allowing synchronization among robots. Slot allocation collisions can also be avoided. The proposed scheme was verified through the ns-3 simulator. The scheme showed a higher packet delivery ratio than the algorithm in comparison. It also performed with shorter delay time in the downlink traffic transmission scenario than the algorithm in comparison.

• Journal of Powder Materials
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• v.24 no.6
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• pp.437-443
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• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• Analytical Science and Technology
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• v.30 no.6
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• pp.405-410
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• 2017

High energetic materials (HEMs) have been used in fuels, civil engineering and architecture as well as military purposes such as explosives and propellants. The essential process for the development of new energetic compounds is to accurately calculate its detonation performances. The most typical equation for calculating the explosive performance is the Kamlet-Jacobs (K-J) equation. In the K-J equation, the parameter such as the number of moles of gaseous products at the explosion, the average molar mass of gas products, and the explosion heat greatly affect the explosion performance. These depend on the product composition for the detonation reaction. In this study, detonation products of 65 high energetic molecules (HEMs) were calculated from the various rules such as Kamlet-Jacobs, Kistiakowsky-Wilson, modified Kistiakowsky-Wilson, Springall-Roberts rules to calculate more accurate detonation velocity (Dv). In addition, they were applied to five kinds of detonation velocity equations proposed by K-J, Rothstein, Xiong, Stine and Keshavarz. The mean absolute error and root mean square error of HEMs were obtained from experimental and calculated velocity value for each method. The K-J and Xiong equation that is slightly complex showed a lower mean absolute error than the simple Rothstein and Keshavarz equation. When the mod-KW rule was applied to the Xiong equation, the detonation velocities were the most accurate. This study compared the various method of calculating the detonation velocity of HEMs to obtain accurate HEMs performance.