• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.759-769
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• 2021

For aerospace propulsion systems, Titanium Hydride Potassium Perchlorate (THPP) is a material commonly used as a pyrotechnic initiator that generates gas when energy is supplied or as a supplement charge for NASA standard initiator (NSI). However, when the energetic materials are stored for a long time, it faces the problem of 'aging'. In this study, changes in thermodynamic properties of THPP aged under various humidity environments were identified through thermal analysis and surface analysis. First, a considerable amount of cracks on the surface of the oxidant was found in the aged THPPs. Particularly, when the humidity level increased, the number and length of the cracks rapidly increased. Also, the deterioration of Viton was found only in the thermally aged sample whereas the oxidation of the fuel was more pronounced in the hygrothermally aged samples. The extracted kinetic parameters of THPP on the reaction progress vary greatly by the humidity level, indicating that moisture significantly changes the performance and combustion reaction of THPP, which may eventually result in a reduced lifespan.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.6
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• pp.66-73
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• 2021

The development of excellent high-energy materials has progressed in the direction of synthesizing compounds with high nitrogen content, ultimately oriented toward the form of polynitrogen. As cyclo-N₅^-, a type of polynitrogen, is synthesized as sodium pentazolate(NaN₅) and the results of various metal and non-metal compounds have been studied, the usage of polynitrogen compounds is attracting attention. However, since the known synthesis and purification method of NaN₅ are very extreme and complicated, it is essential to improve the process in order to increase the utility of the pentazolate compounds in the future. In this study, only a simple filtration method was applied to purify the NaN₅, and based on this, two non-metal pentazolate salt compounds were successfully synthesized.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.

• Resources Recycling
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• v.14 no.3
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• pp.16-36
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• 2005

The quantity of passenger cars in industrial countries has been significantly increased in recent years. According to prognoses, this tendency is likely to continue in the forthcoming future. As a direct consequence, an increase of End-of Life-Vehicles (ELV) will confront us with the problem of "ELV-Recycling". In order to cope with this situation, the European regulation for the treatment of End-of-Life-Vehicles (09/2000) has been transferred to national law in Germany (ELV-Regulation from 1 July 2002). The long term aim is to reduce residues from the ELV-treatment to less than 5 wt% from 30 wt% within the next 10 years (2015). For that reason, there is a need for innovative and more efficient recycling techniques tailored to future materials in automobiles. The design process at automotive industry is continuously changing due to the strong demand on optional equipment and new technical solutions for fuel saving. Light materials, such as aluminum and plastics, consequently become more important and cause a decrease of ferrous metals. Since plastic materials are often used as compounds, a separation into initial material types by means of mechanical recycling methods is not possible. For that reason, efficient recycling can only be realized by introducing recycling-friendly car designs. In the end an integrated approach of auto makers and recycling industry is of decisive significance for the fulfillment of future regulations.

• Journal of Science Education
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• v.34 no.1
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• pp.33-46
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• 2010

The purpose of this study was to find out the image as science teachers recognized by pre-service science teachers. The data was collected from 312 pre-service science teachers from Kyungpook National University in Daegu and participants were asked to write about the image of science teachers they liked most and least in their secondary school years freely. The result of this research was as follows. The image as science teachers categorized 2 factors: science instructional situation, image of science teacher. Each factor was subdivided into more detailed ones. First of all, 'science instructional situation' category subdivided into lesson style, teaching-learning materials, teaching methods, and class atmosphere. In lesson style, 'experiment' and 'observation' gained the most favorable comments, and questioning-answering gained the least. In teaching-learning materials, print materials such as handouts, worksheets, reports were the most liked, and 'writing on the blackboard' was the least liked. In teaching methods, the 'detailed and systematic explanation of the theory and concepts' was preferred to rote learning and memorization lacking explanation. In class atmosphere, friendly and free atmosphere was the most preferred, and uncomfortable, boring one was the least preferred. Secondly, in 'image of the science teachers' category and 'quality as the teachers' sub-category, thoughtful and considerate teachers who respect students' personality was the most preferred. On the contrary, they didn't prefer teachers who were indifferent and humiliated students. Finally in 'characteristics of the teachers' sub-category, the participants liked clear, energetic voice, and mild expression, and they didn't like formal style, overly fancy clothes, etc. Based on the result of this study, more empirical study on the teachers' image is needed, and the thoughts of educational administrators, students, parents, and teachers should be reflected because an undesirable teacher can be advised and get opportunity to be a better teacher.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.3
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• pp.63-70
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• 2016

The pyrotechnic separation devices are widely used in space systems and guided weapons during the launching and operations, however, they generate intensive pyroshock and fragments that can cause critical damages or the malfunction of electric devices onboard. There have been proposed many types of alternative devices to avoid pyro-induced problems since 1960's. A ball-type separation bolt is the one of alternative Pyrotechnic Mechanical Devices (PMD). In this study, the detail separation behavior of the ball-type separation bolt is analyzed using ANSYS AUTODYN. A simplified one-dimensional mathematical model, consisting of a combustion model and 5-stages of differential equation of motions, is also established to effectively describe the entire separation process.

• Journal of Korean Elementary Science Education
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• v.26 no.3
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• pp.276-285
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• 2007

The purpose of this study was to observe five teachers' science classes and analyze the patterns of their analogies. To analyze the data, investigator triangulation was used, and the results were as follows: First, among the patterns of analogy used, expressions of similes and metaphors were utilized by all the teachers; teachers with over ten years' experience used adult's daily phrases, and teachers with under ten years' experience tended to use anthropomorphism. Regarding pictorial analogies, these manifested themselves in the sixth period, while teachers with over ten years' experience drew a simple picture about circulation of water, teachers with under one year's experience made additional materials for their analogy and they put an emphasis on the concept of the circulation itself. Teachers tended to use analogs according to their interests; teachers who majored in science education used pictorial analogies for further study. Second, the patterns emerging from the correspondence of the analogy manifested themselves in all the teachers equally, but they have no relation to the teacher's background. Third, routine analogy and artificial analogy appeared equally in consideration of degree of artificiality among the patterns of the analogies used. Regarding routine analogy, most teachers tended to look for analogs from things and experiences from themselves or their own backgrounds rather than those of the students. Regarding artificial analogies, teachers tended to purposely choose analogs to help students to understand; energetic teachers sometimes failed to choose appropriate analogs because they approached the topic with too much intensity. While a teacher who lacked experience and interest in science used many expressions of analogy, a teacher who felt some degree of constraint rarely used expressions of analogy. Fourth, most of the teachers used analogs familiar to their own experiences but students often found understanding these analogs difficult. Therefore, teachers need to make greater efforts to utilize analogs which are especially familiar to students when they attempt to explain science concepts.

• Journal of the Korean Vacuum Society
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• v.8 no.3B
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• pp.262-268
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• 1999

Polycarbonate (PC) and Polymethylmethacrylate (PMMA) surface was modified by ion assisted reaction (IAR) technique to obtain the hydrophilic functional groups and improve the wettability. In conditions of ion assisted reaction, ion beam energy was changed from 500 to 1500eV, and ion dose and oxygen gas blown rate were fixed $1\times10^{16}$ ions/$\textrm{cm}^2$ and 4ml/min, respectively. Wetting angle of water on PC and PMMA surface modified by $Ar^+$ ion without blowing oxygen at 4ml/mon showed $5^{\circ}$ and $10^{\circ}$. Changes of wetting angle with oxygen gas and $Ar^+$ ion irradiation were explained by considering formation of hydrophilic group due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas. X-ray photoelectron spectroscopy analysis shows that hydrophilic groups such as -C-O, -(C=O)- and -(C=O)-O- are formed on the surface of polymer by chemical interaction. The polymer surface modification using ion assisted reaction only changed the surface physical properties and sept the bulk properties. In comparison with other modification methods, the surface modification by IAR treatment was chemically stable and enhanced the adhesion between metal and polymer surface. The applications of various kinds of polymer surface modification methods, metal and polymer surface. The applications of various kinds of polymer surface modification could be appled to the new materials about hydrophilic surface properties by IAR treatment. The adhesion between metal film and polymer measured by Scotch tape test whether the hydrophilic surfaces could improve the adhesion strength or not.

• Journal of Astronomy and Space Sciences
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• v.32 no.2
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• pp.145-149
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• 2015

A newly designed Tissue Equivalent Proportional Counter (TEPC) has been developed for the CubeSat mission, SIGMA (Scientific cubesat with Instruments for Global Magnetic field and rAdiation) to investigate space radiation. In order to test the performance of the TEPC, we have performed heavy ion beam experiments with the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. In space, human cells can be exposed to complex radiation sources, such as X-ray, Gamma ray, energetic electrons, protons, neutrons and heavy charged particles in a huge range of energies. These generate much a larger range of Linear Energy Transfer (LET) than on the ground and cause unexpected effects on human cells. In order to measure a large range of LET, from 0.3 to $1,000keV/{\mu}m$, we developed a compact TEPC which measures ionized particles produced by collisions between radiation sources and tissue equivalent materials in the detector. By measuring LET spectra, we can easily derive the equivalent dose from the complicated space radiation field. In this HIMAC experiment, we successfully obtained the linearity response for the TEPC with Fe 500 MeV/u and C 290 MeV/u beams and demonstrated the performance of the active radiation detector.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.135-136
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• 1998

By the ion bombardment the original discrete layered structure is damaged and a uniformly mixed layer is formed by the intermixing of the films. Immediately after this dynamic cascade mixing a structure of this mixed layer is likely to be a mixture of randomly distributed atoms. Subsequently the mixed layered structure becomes a non-equilibrium structure such as the metastable pphase because the kinetic energies of the incident ions rappidly dissippate and host atoms within the collision cascade region are quenched from a highly energetic state. The formation of the metastable transition metal alloys using ion-beam-mixing has been extensively studied for many years because of their sppecific ppropperties that differ from those of bulk materials. in ion-beam-mixing the alloy or comppound is formed due to the atomic interaction between different sppecies during ion bombardment. in this study the metastable pphase formed by ion-beam-mixing pprocess is comppared with equilibrium one by arc-melting method by GXRD and XAS. Therfore we studied the fundamental characteristics of charge redistribution uppon alloying and formation of intermetallic comppounds. The multi-layer films were depposited on a wet-oxidized Si(100) substrate by sequential electron beam evapporation at a ppressure of less than 5$\times$10-7 Torr during depposition. These compprise 4 ppairs of Co and ppt layers where thicknesses of each layer were varied in order to change the alloy compposition.