• Journal of the Korean Vacuum Society
• /
• v.18 no.4
• /
• pp.302-309
• /
• 2009

We fabricated a Si nano floating gate memory with Schottky barrier tunneling transistor structure. The device was consisted of Schottky barriers of Er-silicide at source/drain and Si nanoclusters in the gate stack formed by LPCVD-digital gas feeding method. Transistor operations due to the Schottky barrier tunneling were observed under small gate bias < 2V. The nonvolatile memory properties were investigated by measuring the threshold voltage shift along the gate bias voltage and time. We obtained the 10/50 mseconds for write/erase times and the memory window of $\sim5V$ under ${\pm}20\;V$ write/erase voltages. However, the memory window decreased to 0.4V after 104seconds, which was attributed to the Er-related defects in the tunneling oxide layer. Good write/erase endurance was maintained until $10^3$ write/erase times. However, the threshold voltages moved upward, and the memory window became small after more write/erase operations. Defects in the LPCVD control oxide were discussed for the endurance results. The experimental results point to the possibility of a Si nano floating gate memory with Schottky barrier tunneling transistor structure for Si nanoscale nonvolatile memory device.

• Korean Journal of Dental Materials
• /
• v.44 no.3
• /
• pp.263-272
• /
• 2017

In this study, antibacterial chlorhexidine (CHX)-containing hydroxyapatite (HAp) was coated on titanium and investigated its characteristics. Ti-mSBF-CHX group was prepared by soaking titanium disks in the modified simulated body fluid (mSBF) mixed with CHX. Ti-mSBF group was coated using mSBF without CHX. Ti-mSBF-adCHX group was prepared by soaking Ti-mSBF specimen in CHX-containing solution. The crystallines clusters composed with nano-shaped crystallites were coated on the surface of the Ti-mSBF specimen. The ribbon-shaped crystallites were observed with the crystalline clusters on the Ti-mSBF-CHX specimen. The content of CHX chemical compositions was high in ribbon-shaped crystallites. HAp crystalline structure was dominant for all prepared specimens, and ${\beta}-TCP$ (tricalcium phosphate) and OCP (octacalcium phosphate) crystalline structures were observed in the Ti-mSBF-CHX specimen. FT-IR spectra showed the strong peaks of CHX in Ti-mSBF-adCHX and Ti-mSBF-CHX groups. However, after immersing in a phosphate buffered saline (PBS), CHX was rapidly released in Ti-mSBF-adCHX group, while it was slowly released in Ti-mSBF-CHX. We expect that the coating method of Ti-mSBF-CHX group could be used for protecting inflammation of titanium implant by incorporating antibacterial agent CHX into HAp layer.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.1-2
• /
• 2011

Hybrid rockets have lately attracted attention as a strong candidate of small, low cost, safe and reliable launch vehicles. A significant topic is that the first commercially sponsored space ship, SpaceShipOne vehicle chose a hybrid rocket. The main factors for the choice were safety of operation, system cost, quick turnaround, and thrust termination. In Japan, five universities including Hokkaido University and three private companies organized "Hybrid Rocket Research Group" from 1998 to 2002. Their main purpose was to downsize the cost and scale of rocket experiments. In 2002, UNISEC (University Space Engineering Consortium) and HASTIC (Hokkaido Aerospace Science and Technology Incubation Center) took over the educational and R&D rocket activities respectively and the research group dissolved. In 2008, JAXA/ISAS and eleven universities formed "Hybrid Rocket Research Working Group" as a subcommittee of the Steering Committee for Space Engineering in ISAS. Their goal is to demonstrate technical feasibility of lowcost and high frequency launches of nano/micro satellites into sun-synchronous orbits. Hybrid rockets use a combination of solid and liquid propellants. Usually the fuel is in a solid phase. A serious problem of hybrid rockets is the low regression rate of the solid fuel. In single port hybrids the low regression rate below 1 mm/s causes large L/D exceeding a hundred and small fuel loading ratio falling below 0.3. Multi-port hybrids are a typical solution to solve this problem. However, this solution is not the mainstream in Japan. Another approach is to use high regression rate fuels. For example, a fuel regression rate of 4 mm/s decreases L/D to around 10 and increases the loading ratio to around 0.75. Liquefying fuels such as paraffins are strong candidates for high regression fuels and subject of active research in Japan too. Nakagawa et al. in Tokai University employed EVA (Ethylene Vinyl Acetate) to modify viscosity of paraffin based fuels and investigated the effect of viscosity on regression rates. Wada et al. in Akita University employed LTP (Low melting ThermoPlastic) as another candidate of liquefying fuels and demonstrated high regression rates comparable to paraffin fuels. Hori et al. in JAXA/ISAS employed glycidylazide-poly(ethylene glycol) (GAP-PEG) copolymers as high regression rate fuels and modified the combustion characteristics by changing the PEG mixing ratio. Regression rate improvement by changing internal ballistics is another stream of research. The author proposed a new fuel configuration named "CAMUI" in 1998. CAMUI comes from an abbreviation of "cascaded multistage impinging-jet" meaning the distinctive flow field. A CAMUI type fuel grain consists of several cylindrical fuel blocks with two ports in axial direction. The port alignment shifts 90 degrees with each other to make jets out of ports impinge on the upstream end face of the downstream fuel block, resulting in intense heat transfer to the fuel. Yuasa et al. in Tokyo Metropolitan University employed swirling injection method and improved regression rates more than three times higher. However, regression rate distribution along the axis is not uniform due to the decay of the swirl strength. Aso et al. in Kyushu University employed multi-swirl injection to solve this problem. Combinations of swirling injection and paraffin based fuel have been tried and some results show very high regression rates exceeding ten times of conventional one. High fuel regression rates by new fuel, new internal ballistics, or combination of them require faster fuel-oxidizer mixing to maintain combustion efficiency. Nakagawa et al. succeeded to improve combustion efficiency of a paraffin-based fuel from 77% to 96% by a baffle plate. Another effective approach some researchers are trying is to use an aft-chamber to increase residence time. Better understanding of the new flow fields is necessary to reveal basic mechanisms of regression enhancement. Yuasa et al. visualized the combustion field in a swirling injection type motor. Nakagawa et al. observed boundary layer combustion of wax-based fuels. To understand detailed flow structures in swirling flow type hybrids, Sawada et al. (Tohoku Univ.), Teramoto et al. (Univ. of Tokyo), Shimada et al. (ISAS), and Tsuboi et al. (Kyushu Inst. Tech.) are trying to simulate the flow field numerically. Main challenges are turbulent reaction, stiffness due to low Mach number flow, fuel regression model, and other non-steady phenomena. Oshima et al. in Hokkaido University simulated CAMUI type flow fields and discussed correspondence relation between regression distribution of a burning surface and the vortex structure over the surface.

• Korean Journal of Remote Sensing
• /
• v.37 no.5_1
• /
• pp.989-998
• /
• 2021

In the utilization of optical satellite imagery, which is greatly affected by clouds, periodic composite technique is a useful method to minimize the influence of clouds. Recently, a technique for selecting the optimal pixel that is least affected by the cloud and shadow during a certain period by directly inputting cloud and cloud shadow information during period compositing has been proposed. Accurate extraction of clouds and cloud shadowsis essential in order to derive optimal composite results. Also, in the case of an surface targets where spectral information is important, such as crops, the loss of spectral information should be minimized during cloud-free compositing. In thisstudy, clouds using two spectral indicators (Haze Optimized Tranformation and MeanVis) were used to derive a detection technique with low loss ofspectral information while maintaining high detection accuracy of clouds and cloud shadowsfor cabbage fieldsin the highlands of Gangwon-do. These detection results were compared and analyzed with cloud and cloud shadow information provided by Sentinel-2A/B. As a result of analyzing data from 2019 to 2021, cloud information from Sentinel-2A/B satellites showed detection accuracy with an F1 value of 0.91, but bright artifacts were falsely detected as clouds. On the other hand, the cloud detection result obtained by applying the threshold (=0.05) to the HOT showed relatively low detection accuracy (F1=0.72), but the loss ofspectral information was minimized due to the small number of false positives. In the case of cloud shadows, only minimal shadows were detected in the Sentinel-2A/B additional layer, but when a threshold (= 0.015) was applied to MeanVis, cloud shadowsthat could be distinguished from the topographically generated shadows could be detected. By inputting spectral indicators-based cloud and shadow information,stable monthly cloud-free composited vegetation index results were obtained, and in the future, high-accuracy cloud information of Sentinel-2A/B will be input to periodic cloud-free composite for comparison.

• Journal of the Society of Cosmetic Scientists of Korea
• /
• v.45 no.2
• /
• pp.175-184
• /
• 2019

The epidermal growth factor (EGF) has a intrinsic function of inducing growth and proliferation of cells through interacting with cell membrane receptors in human epidermis and dermis layer. These functions of EGF are used as a main ingredient for wound healing medicines and anti-aging cosmetics. As a cosmetic ingredient, the EGF has a problem in exhibiting its natural efficacy due to the lack of the ability to penetrate through the stratum corneum, which is known as the skin barrier. In this study, a recombinant human epidermal growth factor ($MTD_{151}-EGF$) fused with the macromolecule transduction domain $(MTD)_{151}$ with the skin penetration ability was developed to improve the skin penetration efficiency of the EGF. Expression of $MTD_{151}-EGF$ was performed in E. coli transformed with a vector encoding the $MTD_{151}-EGF$ gene and then purified. The purified $MTD_{151}-EGF$ was evaluated using cell proliferation assay, cytotoxicity test and skin penetration test by franz diffusion cell assay and artificial skin. Cell proliferation activity of $MTD_{151}-EGF$ purified to high purity of 99% or above was equivalent to the EGF or better, and cytotoxicity was not observed. In addition, the $MTD_{151}-EGF$ showed an excellent penetration efficiency compared to the EGF in the skin penetration test with EGF and $MTD_{151}-EGF$ labeled by FITC in an artificial skin penetration model. Based on the quantitative analysis of the penetrating substance using franz diffusion cell assay, the amount of penetration was about 16 times more than that of EGF. These results can be regarded as an effective alternative to improve the existing physical transdermal penetration method related to the use of various active ingredients for cosmetics.

• Korean Journal of Heritage: History & Science
• /
• v.51 no.2
• /
• pp.78-91
• /
• 2018

Sangjogam, located in Goseong, Gyeongsangnam-do, was designated as Natural Monument #411, because of its diverse geological heritage, such as fossils, ripple marks, dykes, and columnar joints. In the area, Byeongpungbawi, with its beautiful columnar joints vertical to the bedding plane of the underlying sedimentary rocks and spectacular coastal view, was named after its overall shape reminiscent of a huge folding screen. The purpose of this study was to investigate the formation process of the columnar joints using the anisotropy of magnetic susceptibility (AMS) method. AMS measurements showed that the k1 and k3 values representative of directions of the long and short axes of a magnetic particle at each point strongly clustered, and the oblate magnetic foliation structure in Byeongpungbawi developed during sill-type intrusion rather than lava flow. In summary, Byeongpungbawi was produced by sill-type intrusion along the bedding plane of the underlying sedimentary layer, and the subsequent formation of columnar joints was accompanied by the cooling and contraction of intruding rhyolite magma. This study potentially provides a basic research tool in understanding the formation mechanism of columnar joints which are widely distributed in southern Korea.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.26 no.1
• /
• pp.37-48
• /
• 2021

A new high speed rotation type-passive sampling device (HSR-PSD), which can rotate seawater at high speed and absorb easily and quickly the freely dissolved hydrophobic organic contaminants from seawater, was developed and then applied around the Korean Peninsula. Freely dissolved concentrations (Cfree) of polycyclic aromatic hydrocarbons (PAHs) were determined using the HSR-PSD with low density polyethylene (LDPE) sheets as a passive sampler. Furthermore, dissolved concentrations (Cdissolved) of PAHs in seawater were also obtained from high volume water sampling as a conventional method to account for actual bioavailability. When the LDPE sheets were rotated in the HSR-PSD at 900 rpm, PAHs with log KOW 3.4 ~ 5.2 were equilibrated between the LDPE and water in 5 hours. Although the high molecular weight PAHs with log KOW 5.6 ~ 6.8 was expected to be 2 to 30 days to reach the equilibrium, the Cfree of the PAHs at equilibrium could be corrected using performance reference compounds in 5 hours. Meanwhile, the total Cfree of PAHs were from 0.32 to 1.2 ng/L, which were higher than reported values in other oceans, but lower than in coastal water such as estuary, harbor, or shore. A bioavailability from the detected PAHs was highest at the sampling line near the dumping site of the Yellow Sea. Predicted residual concentrations in biota were relatively higher in offshore including the dumping site than in coastal regions.

• Korean Chemical Engineering Research
• /
• v.60 no.1
• /
• pp.93-99
• /
• 2022

With the rapid development of ultra-small and wearable device technology, continuous electricity supply without spatiotemporal limitations for driving electronic devices is required. Accordingly, Triboelectric nanogenerator (TENG), which utilizes static electricity generated by the contact and separation of two different materials, is being used as a means of effectively harvesting various types of energy dispersed without complex processes and designs due to its simple principle. However, to apply the TENG to real life, it is necessary to increase the electrical output. In addition, stable generation of electrical output, as well as increase in electrical output, is a task to be solved for the commercialization of TENG. In this study, we proposed a method to not only improve the output of TENG but also to stably represent the improved output. This was solved by using the contact layer, which is one of the components of TENG, as an electret for improved output and stability. The utilized electret was manufactured by sequentially performing corona charging-thermal annealing-corona charging on the Fluorinated ethylene propylene (FEP) film. Electric charges artificially injected due to corona charging enter a deep trap through the thermal annealing, so an electret that minimizes charge escape was fabricated and used in TENG. The output performance of the manufactured electret was verified by measuring the voltage output of the TENG in vertical contact separation mode, and the electret treated to the corona charging showed an output voltage 12 times higher than that of the pristine FEP film. The time and humidity stability of the electret was confirmed by measuring the output voltage of the TENG after exposing the electret to a general external environment and extreme humidity environment. In addition, it was shown that it can be applied to real-life by operating the LED by applying an electret to the clap-TENG with the motif of clap.

• Korean Journal of Remote Sensing
• /
• v.38 no.6_1
• /
• pp.1463-1478
• /
• 2022

Maritime transport accounts for 99.7% of the exports and imports of the Republic of Korea; therefore, developing a vessel monitoring system for efficient operation is of significant interest. Several studies have focused on tracking and monitoring vessel movements based on automatic identification system (AIS) data; however, ships without AIS have limited monitoring and tracking ability. High-resolution optical satellite images can provide the missing layer of information in AIS-based monitoring systems because they can identify non-AIS vessels and small ships over a wide range. Therefore, it is necessary to investigate vessel monitoring and small vessel classification systems using high-resolution optical satellite images. This study examined the possibility of developing ship monitoring systems using Compact Advanced Satellite 500-1 (CAS500-1) satellite images by first training a deep learning model using satellite image data and then performing detection in other images. To determine the effectiveness of the proposed method, the learning data was acquired from ships in the Yellow Sea and its major ports, and the detection model was established using the You Only Look Once (YOLO) algorithm. The ship detection performance was evaluated for a domestic and an international port. The results obtained using the detection model in ships in the anchorage and berth areas were compared with the ship classification information obtained using AIS, and an accuracy of 85.5% and 70% was achieved using domestic and international classification models, respectively. The results indicate that high-resolution satellite images can be used in mooring ships for vessel monitoring. The developed approach can potentially be used in vessel tracking and monitoring systems at major ports around the world if the accuracy of the detection model is improved through continuous learning data construction.

• Korean Journal of Environment and Ecology
• /
• v.35 no.6
• /
• pp.579-593
• /
• 2021

In order to understand the types of vegetation in warm temperate-climate zones, vegetation was investigated in several island areas in Jeollanam-do (Jindo, Wando, Gangjin, Goheung, and Yeosu). The evaluation standard for degraded level of warm temperate forests were proposed based on the importance percentage (IP) in canopy layer of the evergreen broad-leaf forests and the number of arboreal evergreen broad-leaf species. Through these measurements, the restoration types and techniques for each degraded level were estimated, and it is intended to be used in establishing restoration plans for the southwest coast island area. The vegetation was analyzed using the two-way indicator species analysis (TWINSPAN) method using survey data of 307 plots. As a result, it was divided into 8 communities, and the appearance characteristics of evergreen broad-leaf species were identified in each community. Community I was located on the lower slope at an altitude of 86.6 m, and Neolitsea sericea and Castanopsis sieboldii were dominant. Communities II and III were the vegetation types that appear on the coast below an altitude of 10.5 to 22.5 m, and Machilus thunbergii, Cinnamomum japonicum, N. sericea, and C. sieboldii were dominant. Communities IV and V were vegetation types that appeared in the lower and middle slops between the altitudes of 71.9 to 153.4m, and C. sieboldii was dominant. In community VI, the N. sericea was dominant in the lower and middle slops at an altitude of 166.9 m. The last communities VII and VIII were the vegetation types that appeared on the middle slop at an altitude of 187.8 to 246.2 m. Also, Quercus acuta and Q. salicina were present. In summary, the evergreen broad-leaf forests dominated by M. thunbergii, C. japonicum, and N. sericea appeared mainly in the coastal areas of the lowlands. The community of C. sieboldii was distributed higher inland than this community. The communities that appeared mainly in the inland highlands at levels above these two communities were Q. acuta and Q. salicina. The degraded level was classified as 0 to V, according to the IP of arboreal evergreen broad-leaf species and the number of arboreal evergreen broad-leaf species. According to the degraded level, the restoration types (preservation, induction, improvement, creation) and the restoration techniques were determined.