• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.9
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• pp.944-950
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• 2013

This paper is a study of a rain sensor using an open-ended coaxial cavity resonator which senses the amount of rain drops linearly. It shows that it will be used as a sensor to sense the amount of rain dropped on the windshield of an automobile based on the principle of varied resonant frequency and the loss according to the amount and characteristics of an dielectric lied on the open side of a resonator. The input and output ports are built in the both sides of the resonator and the input and output coupling probes are formed like 'ㄱ' shape. The response of rain drops were simulated by the radius of inner conductor of 2 mm, 5 mm, and 10 mm respectively and it showed that the raindrop was sensed most linearly and sensitively when the radius of inner conductor is 5 mm, We have measured that the resonant frequency have varied from 3.55 GHz to 3 GHz and the Q value have varied from 42.38 to 24.3 according to the variation of rain drop amount on the fabricated resonator. Therefore, it shows that the designed resonator can be applied as a rain sensor that measures the amount of rain drops linearly by using the resonant frequency as a measurement parameter.

• Journal of Periodontal and Implant Science
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• v.38 no.1
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• pp.97-102
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• 2008

Purpose: Periodontal intrabony defects have great deal of importance since they contribute to the development of periodontal disease. Current treatment regimens for intrabony defects involve grafting of numerous bony materials, GTR using biocompatible barriers, and biomodification of root surface that will encourage the attachment of connective tissue. Xenograft using deproteinized bovine bone particles seems to be very convenient to adjust because it doesn't require any donor sites or imply the danger of cross infections. These particles are similar to human cancellous bone in structure and turned out to be effective in bone regeneration in vivo. We here represent the effectiveness of grafting deproteinized bovine bone particles in intrabony defect and furcation involvements that have various numbers of bony walls. Materials and methods: Open flap debridement was done to remove all root accretions and granulation tissue from the defects within persisting intrabony lesions demonstrating attachment loss of over 6mm even 3 months after nonsurgical periodontal therapy have been completed. Deproteinized bovine bone particles($BBP^{(R)}$, Oscotec, Seoul) was grafted in intrabony defects to encourage bone regeneration. Patients were instructed of mouthrinses with chlorohexidine-digluconate twice a day and to take antibiotics 2-3 times a day for 2 weeks. They were check-up regularly for oral hygiene performance and further development of disease. Probing depth, level of attachment and mobility were measured at baseline and 6 months after the surgery. The radiographic evidence of bone regenerations were also monitored at least for 6 months. Conclusion: In most cases, radio-opacities increased after 6 months. 2- and 3-wall defects showed greater improvements in pocket depth reduction when compared to 1-wall defects. Class I & II furcation involvements in mandibular molars demonstrated the similar results with acceptable pocket depth both horizontally and vertically comparable to other intrabony defects. Exact amount of bone gain could not be measured as the re-entry procedure has not been available. With in the limited data based on our clinical parameter to measure pocket depth reduction following $BBP^{(R)}$ grafts, it was comparable to the results observed following other regeneration techniques such as GTR.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.256-262
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• 2000

The dielectric properties of complex perovskite ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ with >($0.5{\le}x{\ge}0.65$ were investigated at microwave frequencies. Dilectric constant decreased with increasing Ca content, and was directly proportional to the cube of average ionic ra야 of A-site. For the specimen of x=0.6 sintered at $1250^{\circ}C$ for 3 h in air, dielectric constant (k) of 63, QF of 11000 GHz, and the temperature coefficient of resonant frequency(TCF) of -14ppm/$^{\circ}C$ were obtained. As Ca content increased, TCF of the specimen negatively increased due to the reduction of the tolerance factor(t). Changes in intrinsic loss with varying Ca content was investigated by the infrared reflectivity spectra ranging 50 to 4000 $cm^{-1}$, which were calculated by the Kramers-Kronig analysis and classical oscillator model. The relative tendency of microwave dielectric properties of the ($Pb_{1-x}Ca_{x}$)($Fe_{0.5}Ta_{0.5}$)$O_{3}$ specimens calculated from the reflectivity data were in good agreement with the results by the post resonant method.

• Journal of the Korean Ceramic Society
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• v.43 no.12 s.295
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• pp.812-822
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• 2006

This study amis to investigate the functional analysis of anode and cathode materials in Anode supported Solid Oxide Fuel Cell. The concentration polarization of single cell was investigated with CFD (Computational Fluid Dynamics) method for the case of the different morphology by using four types of unit cell and discussed to reduce the concentration polarization. The concentration polarization at anode side effected the voltage loss in Anode supported Solid Oxide Fuel Cell and increased contact areas between fuel gas and anode side could reduce the concentration polarization. For intermediate temperature operation, Anode-supported single cells with thin electrolyte layer of YSZ (Yttria-Stabilized Zirconia) were fabricated and short stacks were built and evaluated. We also developed diesel and methane autothermal reforming (ATR) reactors in order to provide fuels to SOFC stacks. Influences of the $H_2O/C$ (steam to carbon ratio), $O_2/C$ (oxygen to carbon ratio) and GHSV (Gas Hourly Space Velocity) on performances of stacks have been investigated. Performance of the stack operated with a diesel reformer was lower than with using hydrogen as a fuel due to lower Nernst voltage and carbon formation at anode side. The stack operated with a natural gas reformer showed similar performances as with using hydrogen. Effects of various reformer parameters such as $H_2O/C$ and $O_2/C$ were carefully investigated. It is found that $O_2/C$ is a sensitive parameter to control stack performance.

• Korean Journal of Remote Sensing
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• v.31 no.6
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• pp.513-521
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• 2015

In the processing of ocean color remote sensing data, spatio-temporal binning is crucial for securing effective observation area. The validity determination for given source data refers to the information in Level-2 flag. For minimizing the stray light contamination, NASA OBPG's standard algorithm suggests the use of large filtering window but it results in the loss of effective observation area. This study is aimed for quality improvement of ocean color remote sensing data by recovering/extending the portion of effective observation area. We analyzed the difference between MODIS/Aqua standard and modified product in terms of chlorophyll-a concentration, spatial and temporal coverage. The recovery fractions in Level-2 swath product, Level-3 daily composite product, 8-day composite product, and monthly composite product were $13.2({\pm}5.2)%$, $30.8({\pm}16.3)%$, $15.8({\pm}9.2)%$, and $6.0({\pm}5.6)%$, respectively. The mean difference between chlorophyll-a concentrations of two products was only 0.012%, which is smaller than the nominal precision of the geophysical parameter estimation. Increase in areal coverage also results in the increase in temporal density of multi-temporal dataset, and this processing gain was most effective in 8-day composite data. The proposed method can contribute for the quality enhancement of ocean color remote sensing data by improving not only the data productivity but also statistical stability from increased number of samples.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.261-275
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• 2020

When excavating a small cross-section tunnel in a fault fracture zone using the shield TBM method, there is a high possibility of excessive convergence and collapse. Appropriate ground reinforcement is required to minimize construction cost loss and trouble due to a fault fracture zone. In this study, the optimal reinforcement area was suggested and the surrounding ground behavior was investigated through numerical analysis using MIDAS GTS NX (Ver. 280). For the parameters, the width of the fault fracture zone, the existence of fault gouge, and the groundwater level and depth of cover were applied. As a result, when there is not fault gouge, the convergence and ground settlement are satisfied the standard when applying ground reinforcement by up to 0.5D. And, due to the high permeability coefficient, it is judged that it is necessary to apply 0.5D reinforcement. There is a fault gouge, it was possible to secure stability when applying ground reinforcement between the entire fault fracture zone from the top of the tunnel to 0.5D. And, because the groundwater discharge occurred within the standard value due to the fault gouge, reinforcement was unnecessary.

• Korean Journal of Optics and Photonics
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• v.12 no.2
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• pp.135-142
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• 2001

Recently, plastic optical fiber draws a lot of attention as a new transmission medium for local area network (LAN) and home network applications. As PMMA based GI-POF (Graded Index Plastic Optical Fiber) has very low loss at about 500 nm and 650 nm wavelengths, it is very important to have a compact ultra short optical pulse source at these wavelength windows. In this paper, we have investigated detailed characteristics of gain switched laser system by using a commercially available low cost RF devices and an InGaAlP Fabry Perot semiconductor laser operating at 650 nm wavelength. The shortest optical 'pulse obtained was 33 psec with 1 GHz repetition rate. Depending on the DC bias current and the modulation frequency, the FWHM and the pulse energy of the gain switched pulses show 33.3-82.8 psec and 0.97-9.69 pI respectively. Also, the spectral bandwidths for CW and gain switched operations are 0.44 nm and 1.50 nm. We believe that these results are quite useful for high bit rate optical transmission applications with PMMA based plastic optical fibers in addition to estimate properties of ultra fast optical components and electro-optic devices. vices.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.3
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• pp.181-189
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• 2019

In this study, a triple-band antenna that can be used in WLAN(Wireless Local Area Network) at 2.4 GHz, 5.8 GHz, and 5G at 3.5 GHz is fabricated. The proposed antenna uses a parasitic element to show the triple band, and the reflector is used at a distance of ${\lambda}/4$ from the antenna to reduce the Specific Absorption Rate(SAR). Its dimensions are $100{\times}75{\times}1.6mm^3$ and each parameter value is optimized for better performance and a lower SAR value. As a result, we obtained a bandwidth of 540 MHz(2.02~2.56 GHz), 390 MHz(3.39~3.78 GHz), and 1,210 MHz(5.56~6.77 GHz) based on the reflection loss factor of -10 dB. In addition, the SAR values of the antenna with reflector are observed to reduce below the SAR value of international standard.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.3
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• pp.415-421
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• 2021

This study analyzed the effect on the cooling performance of the channel shape of a heat sink for an insulated gate bipolar transistor (IGBT). A serpentine channel was used for this analysis, and the parameter for the analysis was the number of curves. The analysis was conducted using computational fluid dynamics with the commercial software ANSYS fluent. One curve in the channel improved the heat dissipation performance of the heat sink by up to 8% compared to a straight-channel heat sink. However, two curves in the channel could not improve the heat discharge performance further. Instead, the two curves caused a higher pressure drop, which induces parasitic loss for the pumping of coolant. The pressure drop of the two-curve channel case was 2.48-2.55 times larger than that of a one-curve channel. This higher pressure drop decreased the heat discharge efficiency of the heat sink with two curves. The discharge heat per unit pressure drop was calculated, and the result of the straight heat sink was highest among the analyzed cases. This means that the heat discharge efficiency of the straight heat sink is the highest.

• Journal of Convergence for Information Technology
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• v.11 no.6
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• pp.1-6
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• 2021

In the field of speech recognition, as the DNN is applied, the use of speech recognition is increasing, but the amount of calculation for parallel training needs to be larger than that of the conventional GMM, and if the amount of data is small, overfitting occurs. To solve this problem, we propose an efficient method for robust voice feature extraction and voice signal noise removal even when the amount of data is small. Speech feature extraction efficiently extracts speech energy by applying the difference in frame energy for speech and the zero-crossing ratio and level-crossing ratio that are affected by the speech signal. In addition, in order to remove noise, the noise of the speech signal is removed by removing the noise of the speech signal with an average predictive improved LMS filter with little loss of speech information while maintaining the intrinsic characteristics of speech in detection of the speech signal. The improved LMS filter uses a method of processing noise on the input speech signal by adjusting the active parameter threshold for the input signal. As a result of comparing the method proposed in this paper with the conventional frame energy method, it was confirmed that the error rate at the start point of speech is 7% and the error rate at the end point is improved by 11%.