• Wind and Structures
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• v.19 no.4
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• pp.421-441
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• 2014

With the assistance of typhoon field data at aerial elevation level observed by meteorological satellites and wind velocity and direction records nearby the ground gathered in Guangzhou Weather Station between 1985 and 2001, some key wind field parameters under typhoon climate in Guangzhou region were calibrated based on Monte-Carlo stochastic algorithm and Meng's typhoon numerical model. By using Peak Over Threshold method (POT) and Generalized Pareto Distribution (GPD), Wind field characteristics during typhoons for various return periods in several typical engineering fields were predicted, showing that some distribution rules in relation to gradient height of atmosphere boundary layer, power-law component of wind profile, gust factor and extreme wind velocity at 1-3s time interval are obviously different from corresponding items in Chinese wind load Codes. In order to evaluate the influence of typhoon field parameters on long-span flexible bridges, 1:100 reduced-scale wind field of type B terrain was reillustrated under typhoon and normal conditions utilizing passive turbulence generators in TJ-3 wind tunnel, and wind-induced performance tests of aero-elastic model of long-span Guangzhou Xinguang arch bridge were carried out as well. Furthermore, aerodynamic admittance function about lattice cross section in mid-span arch lib under the condition of higher turbulence intensity of typhoon field was identified via using high-frequency force-measured balance. Based on identified aerodynamic admittance expressions, Wind-induced stochastic vibration of Xinguang arch bridge under typhoon and normal climates was calculated and compared, considering structural geometrical non-linearity, stochastic wind attack angle effects, etc. Thus, the aerodynamic response characteristics under typhoon and normal conditions can be illustrated and checked, which are of satisfactory response results for different oncoming wind velocities with resemblance to those wind tunnel testing data under the two types of climate modes.

• Restorative Dentistry and Endodontics
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• v.48 no.1
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• pp.1.1-1.11
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• 2023

Objectives: This study evaluated the dentinal penetration depth of 2.5% sodium hypochlorite (NaOCl) in root canals with and without preparation and different irrigant activation protocols. Materials and Methods: Sixty-three bovine mandibular incisors were randomly allocated to 6 groups (n = 10): G1, preparation + conventional needle irrigation (CNI); G2, preparation + passive ultrasonic irrigation (PUI); G3, preparation + Odous Clean (OC); G4, no preparation + CNI; G5, no preparation + PUI; G6, no preparation + OC; and CG (negative control; n = 3). Samples were filled with crystal violet for 72 hours. Irrigant activation was performed. Samples were sectioned perpendicularly along the long axis, 3 mm and 7 mm from the apex. Images of the root thirds of each block were captured with a stereomicroscope and analyzed with an image analysis software. One-way analysis of variance, followed by the Tukey post hoc test, and the Student's t-test were used for data analysis, with a significance level of 5%. Results: The NaOCl penetration depth was similar when preparation was performed, regardless of the method of irrigation activation (p > 0.05). In the groups without preparation, G6 showed greater NaOCl penetration depth (p < 0.05). The groups without preparation had a greater NaOCl penetration depth than those with preparation (p = 0.0019). Conclusions: The NaOCl penetration depth was similar in groups with root canal preparation. Without root canal preparation, OC allowed deeper NaOCl penetration. The groups without preparation had greater NaOCl penetration than those undergoing root canal preparation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.12
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• pp.1069-1077
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• 2011

In this paper, a design and fabrication of a miniaturized 2.5 GHz 8 W power amplifier using selectively anodized aluminum oxide(SAAO) substrate are presented. The process of SAAO substrate is recently proposed and patented by Wavenics Inc. which uses aluminum as wafer. The selected active device is a commercially available GaN HEMT chip of TriQuint company, which is recently released. The optimum impedances for power amplifier design were extracted using the custom tuning jig composed of tunable passive components. The class-F power amplifier are designed based on EM co-simulation of impedance matching circuit. The matching circuit is realized in SAAO substrate. For integration and matching in the small package module, spiral inductors and single layer capacitors are used. The fabricated power amplifier with $4.4{\times}4.4\;mm^2$ shows the efficiency above 40 % and harmonic suppression above 30 dBc for the second(2nd) and the third(3rd) harmonic at the output power of 8 W.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.348-351
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• 2006

Bipolar plate, which forms about 50% of the stack cost, is an important core part with polymer electrolyte membrane in PEMFC. Bipolar plates have been commonly fabricated from graphite meterial having high electrical conductivity and corrosion resistance. Lately, many researchers have concentrated their efforts on the development of metallic bipolar plate and stainless steel has been considered as a potential material for metallic bipolar plate because of its high strength, chemical stability, low gas permeability and applicability to mass production. However, it has been reported that its inadequate corrosion behavior under PEMFC environment lead to a deterioration of membrane by dissolved metal ions and an increase in contact resistance by the growth of passive film therefore, its corrosion resistance as well as contact resistance must be improved for bipolar plate application. In this work, several types of coating were applied to 316L and their electrical conductivity and corrosion resistance were evaluated In the simulated PEMFC environment. Application of coating gave rise to low interfacial contact resistances below $19m{\Omega}cm^2$ under the compress force of $150N/cm^2$. It also made the corrosion potential to shift in the posit ive direct ion by 0.3V or above and decreased the corrosion current from ca. $9{\mu}A/cm^2$ to ca. $0.5{\mu}A/cm^2$ in the mixed solution of $0.1N\;N_2SO_4$ and 2ppm HF A coat ing layer under potentiostatic control of 0.6V and $0.75V_{SCE}$ for 500 hours or longer showed some instabilities, however, no significant change in coat Ing layer were observed from Impedance data. In addition, the corrosion current maintained less than $1{\mu}A/cm^2$ for most of time for potentiostatic tests. It indicates that high electrical conductivity and corrosion resistance can be obtained by application of coatings in the present work.

• Journal of Korea Multimedia Society
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• v.14 no.3
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• pp.414-422
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• 2011

The paper is for top and bottom symmetrical phase controlled loop antenna using for multi-media devices. We developed a top and bottom phase control loop pattern arrangement methods for loop antenna in mobile devices like as a cell phone and PCS, WCDMA. In the loop antenna pattern, arrange close adhesive the loop antenna pattern $180^{\circ}$ cycle in wave length, the radiated electro-magnetic wave from close adhesive loop pattern in $180^{\circ}$ become to coherent wave than the phase controlled loop antenna has high efficiency and high radiation gain. To acquire a wide band width on phase controlled loop antenna, we arrange a top and bottom symmetrical architecture loop pattern that bas a $180^{\circ}$ wave length in each layer. Top and bottom each layer bas a U form pattern separated $90^{\circ}$ wave length each other. This architecture cause a well balanced electro-magnetic flow control that acquired wide bandwidth resonance response in loop pattern antenna. In experiment, we designed a WCDMA mobile multi-media antenna in $40mm{\times}6mm$ area thickness 0.2mm, in that passive experiment the radiation efficiency is over 50% and over 0dBi radiation average gain was acquired, in the active experiment in real multi-media device we acquired -4dBi average gain and 43% transmit/receive efficiency.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.41
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• pp.52.1-52.8
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• 2019

Background: A compact passive oxide layer can grow on tantalum (Ta). It has been reported that this oxide layer can facilitate bone ingrowth in vivo though the development of bone-like apatite, which promotes hard and soft tissue adhesion. Thus, Ta surface treatment on facial implant materials may improve the tissue response, which could result in less fibrotic encapsulation and make the implant more stable on the bone surface. The purposes of this study were to verify whether surface treatment of facial implant materials using Ta can improve the biohistobiological response and to determine the possibility of potential clinical applications. Methods: Two different and commonly used implant materials, silicone and expanded polytetrafluoroethylene (ePTFE), were treated via Ta ion implantation using a Ta sputtering gun. Ta-treated samples were compared with untreated samples using in vitro and in vivo evaluations. Osteoblast (MG-63) and fibroblast (NIH3T3) cell viability with the Ta-treated implant material was assessed, and the tissue response was observed by placing the implants over the rat calvarium (n = 48) for two different lengths of time. Foreign body and inflammatory reactions were observed, and soft tissue thickness between the calvarium and the implant as well as the bone response was measured. Results: The treatment of facial implant materials using Ta showed a tendency toward increased fibroblast and osteoblast viability, although this result was not statistically significant. During the in vivo study, both Ta-treated and untreated implants showed similar foreign body reactions. However, the Ta-treated implant materials (silicone and ePTFE) showed a tendency toward better histological features: lower soft tissue thickness between the implant and the underlying calvarium as well as an increase in new bone activity. Conclusion: Ta surface treatment using ion implantation on silicone and ePTFE facial implant materials showed the possibility of reducing soft tissue intervention between the calvarium and the implant to make the implant more stable on the bone surface. Although no statistically significant improvement was observed, Ta treatment revealed a tendency toward an improved biohistological response of silicone and ePTFE facial implants. Conclusively, tantalum treatment is beneficial and has the potential for clinical applications.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.447-451
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• 2007

We investigated the dependence of the various annealing conditions and thickness ($6\sim45nm$) of the Ti-doped $Al_2O_3$ coating on the electrochemical properties and the capacity fading of Ti-doped $Al_2O_3$ coated $LiCoO_2$ films. The Ti-doped-$Al_2O_3$-coating layer and the cathode films were deposited on $Al_2O_3$ plate substrates by RF-magnetron sputter. Microstructural and electrochemical properties of Ti-doped-$Al_2O_3$-coated $LiCoO_2$ films were investigated by transmission electron microscopy (TEM) and a dc four-point probe method, respectively. The cycling performance of Ti-doped $Al_2O_3$ coated $LiCoO_2$ film was improved at higher cut-off voltage. But it has different electrochemical properties with various annealing conditions. They were related on the microstructure, surface morphology and the interface condition. Suppression of Li-ion migration is dominant at the coating thickness >24.nm during charge/discharge processes. It is due to the electrochemically passive nature of the Ti-doped $Al_2O_3$ films. The sample be made up of Ti-doped $Al_2O_3$ coated on annealed $LiCoO_2$ film with additional annealing at $400^{\circ}C$ had good adhesion between coating layer and cathode films. This sample showed the best capacity retention of $\sim92%$ with a charge cut off of 4.5 V after 50 cycles. The Ti-doped $Al_2O_3$ film was an amorphous phase and it has a higher electrical conductivity than that of the $Al_2O_3$ film. Therefore, the Ti-doped $Al_2O_3$ coated improved the cycle performance and the capacity retention at high voltage (4.5 V) of $LiCoO_2$ films.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1A
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• pp.33-43
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• 2010

Recently, users want to use real-time multimedia services, such as internet, VoIP, etc., using their IEEE 802.11 wireless lan mobile stations. In order to provide such services, a handoff among access points is essential to support the mobility of a node, in such an wide area. However, the legacy handoff methods of IEEE 802.11 technology are easy to lose connections. Also, the recognition of a disconnection and channel re-searching time make the major delay of the next AP to connect. In addition, because IEEE 802.11 decides the selection of an AP depending only on received signal strength, regardless of a node direction, position, etc., it cannot guarantee a stable bandwidth for communication. Therefore, in order to provide a real-time multimedia service, a node must reduce the disconnection time and needs an appropriate algorithm to support a sufficient communication bandwidth. In this paper, we suggest an algorithm which predicts a handoff point of a moving node by using GPS location information, and guarantees a high transmission bandwidth according to the signal strength and the distance. We implemented the suggested algorithm, and confirmed the superiority of our algorithm by reducing around 3.7ms of the layer-2 disconnection time, and guaranteed 24.8% of the communication bandwidth.

• Korean Journal of Remote Sensing
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• v.39 no.6_2
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• pp.1605-1613
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• 2023

The physical properties of the ocean interior are determined by temperature and salinity. To observe them, we rely on satellite observations for broad regions of oceans. However, the satellite for salinity measurement, Soil Moisture Active Passive (SMAP), has low temporal and spatial resolutions; thus, more is needed to resolve the fast-changing coastal environment. To overcome these limitations, the algorithm to use the Geostationary Ocean Color Imager-II (GOCI-II) of the Geo-Kompsat-2B (GK-2B) was developed as the inputs for a Multi-layer Perceptron Neural Network (MPNN). The result shows that coefficient of determination (R²), root mean square error (RMSE), and relative root mean square error (RRMSE) between GOCI-II based sea surface salinity (SSS) (GOCI-II SSS) and SMAP was 0.94, 0.58 psu, and 1.87%, respectively. Furthermore, the spatial variation of GOCI-II SSS was also very uniform, with over 0.8 of R² and less than 1 psu of RMSE. In addition, GOCI-II SSS was also compared with SSS of Ieodo Ocean Research Station (I-ORS), suggesting that the result was slightly low, which was further analyzed for the following reasons. We further illustrated the valuable information of high spatial and temporal variation of GOCI-II SSS to analyze SSS variation by the 11th typhoon, Hinnamnor, in 2022. We used the mean and standard deviation (STD) of one day of GOCI-II SSS, revealing the high spatial and temporal changes. Thus, this study will shed light on the research for monitoring the highly changing marine environment.

• Journal of the Korean earth science society
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• v.28 no.1
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• pp.64-74
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• 2007

The marine seismic prospecting using a research vessel in the shallow sea near the coastal area has certain limits according to the water depth and survey environment. Also, for the electrical resistivity survey at seashore area, one may need a specially designed high-voltage source to penetrate the very conductive surface layer. Therefore, we have conducted a feasibility study on the application of magnetotelluric method (MT), a passive geophysical method, on investigating of shallow marine environment geology. Our study involves both theoretical modeling and field survey at the tidal flat area which represent the very shallow marine environment. We have applied the audio-frequency magnetotelluric (AMT) method to the intertidal deposits of Gunhung Bay, west coast of Korea, and analysed the field data both qualitatively and quantitatively to investigate the morphology and sedimentary stratigraphy of the tidal flat. The inversion of AMT data well reveals the upper sedimentary layer of Holocene intertidal sediments having a range of 13-20 m thickness and the erosional patterns at the unconformable contact boundary. However, the AMT inversion results tend to overestimate the depth of basement (30-50 m) when compared with the seismic section (27-33 m). Since MT responses are not significantly sensitive to the resistivity of middle layer or the depth of basement, the AMT inversion result for basement may have to be adjusted using the comparison with other geophysical information like seismic section or logging data if possible. But, the AMT method can be an effective alternative choice for investigating the seashore area to get important basic informations such as the depositional environment of the tidal flat, sea-water intrusion and the basement structure near the sea shore.