• Applied Chemistry for Engineering
• /
• v.28 no.3
• /
• pp.351-354
• /
• 2017

An experimental design method was used to optimize the synthesis of gamma-alumina with a superior thermal stability using the reverse micelle method. First, twelve experimental conditions were derived by using the mixture design method to optimize conditions for the ratio of surfactant, water and oil, which are main factors in the synthesis process. When the particles synthesized by reverse micelle method were calcined at $900^{\circ}C$ under the designed condition, they all had gamma-alumina crystal structure although there were differences in particle sizes. The coefficient of determination of the second-order regression model using the derived experimental results was 93.68% and the P-value was 0.002. The synthesis conditions forgamma-alumina with various particle sizes were presented using surface and contour lines. As a result, it was calculated that the smallest particle size of about 2.8 nm was synthesized when the ratio of surfactant/water/oil was 0.3450/0.0729/0.5821.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.45 no.6
• /
• pp.87-93
• /
• 2008

This paper describes implementation of the 5.0GHz RF frequency synthesizer with $0.18{\mu}m$ silicon CMOS technology being used as an application of the IEEE802.15.4 USN sensor node transceiver modules. To get good performance of speed and noise, design of the each module like VCO, prescaler, 1/N divider, fractional divider with ${\Sigma}-{\Delta}$ modulator, and common circuits of the PLL has been optimized. Especially to get good performance of speed, power consumption, and wide tuning range, N-P MOS core structure has been used in design of the VCO. The chip area including pads for testing is $1.1*0.7mm^2$, and the chip area only core for IP in SoC is $1.0*0.4mm^2$. Through comparing and analysing of the designed two kind of the frequency synthesizer, we can conclude that if we improve a litter characteristics there is no problem to use their as IPs.

• The Journal of the Acoustical Society of Korea
• /
• v.21 no.1
• /
• pp.62-68
• /
• 2002

It is well known that the MDVR beamforming outperforms the conventional delay-sum beamformer in the sense of noise rejection and bearing resolution. However, the MDVR method requires long observation time to achieve high frequency resolution. The STMV method uses the steered covariance matrix of sensor data, so it has an ability to form an adaptive weight vector from a single time-series snapshot. But it uses the same weight vector across all frequencies. In this paper, we propose an SSMV method. The basic idea of the SSMV method is to decompose a full frequency band into several subbands to acquire a weight vector for each subband, individually. Also the wrap may be divided into several subarrays in order to reduce a computational load and the bandwidth of each subband. Simulations using real sea trial data show that the proposed SSMV method has good performance with short observation time.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.17 no.9
• /
• pp.1996-2002
• /
• 2013

In this paper, a design method for a compact broadband planar monopole antenna fed by a coplanar waveguide (CPW) is studied. The proposed broadband monopole is optimized for terrestrial digital television (DTV) reception. In order to achieve broadband characteristics, the monopole and ground conductor are gradually tapered. By loading slit pairs on both monopole and ground plane, the proposed antenna is miniaturized. The monopole is fed by a CPW with 75-ohm characteristic impedance on an FR4 substrate and its size is $100mm{\times}200mm$. The optimized monopole antenna for DTV band (470-806 MHz) is fabricated on an FR4 substrate and tested experimentally to verify the results of this study.

• Journal of the Institute of Electronics Engineers of Korea CI
• /
• v.37 no.6
• /
• pp.32-40
• /
• 2000

In this paper, we proposed a wavelet-based digital watermarking algorithm using human visual system and subband-adaptive threshold. After the original image is transformed by discrete wavelet transform, the perceptually significant coefficients of the each subband excluding the lowest level subbands are utilized to embed the watermark. To select perceptually significant coefficients for each subband, we use subband-adaptive threshold. For the selected coefficients in the high frequency subbands, the watermark is embedded using HVS. For those of the baseband, the watermark is embedded by conventional embedding method. We tested the performance of the proposed algorithm compared with conventional watermarking algorithm by computer simulation. The experimental results show that the proposed watermarking algorithm is less visible to human eyes and more robust to image compressions, image processings, and geometric transformations than the conventional algorithm.

• Journal of Biomedical Engineering Research
• /
• v.17 no.1
• /
• pp.121-128
• /
• 1996

This paper presents the ECG data compression method referred the adaptive fractal interpolation algorithm. In the previous piecewise fractal interpolation(PFI) algorithm, the size of range is fixed So, the reconstruction error of the PFI algorithm is nonuniformly distributed in the part of the original ECG signal. In order to improve this problem, the adaptive fractal interpolation(AEI) algorithm uses the variable range. If the predetermined tolerance was not satisfied, the range would be subdivided into two equal size blocks. large ranges are used for encoding the smooth waveform to yield high compression efficiency, and the smaller ranges are U for encoding rapidly varying parts of the signal to preserve the signal quality. The suggested algorithm was evaluated using MIT/BIH arrhythmia database. The AEI algorithm was found to yield a relatively low reconstruction error for a given compression ratio than the PFI algorithm. In applications where a PRD of about 7.13% was acceptable, the ASI algorithm yielded compression ratio as high as 10.51, without any entropy coding of the parameters of the fractal code.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.22 no.1
• /
• pp.169-174
• /
• 2018

In this paper, a design method for a wideband LPF for harmonic suppression applications is investigated. The proposed wideband LPF is comprised of four circular slot pairs with different diameters, which are added symmetrically in the ground plane of a CPW transmission line. Four circular slot pairs act as a defected ground structure and provide a wideband low pass characteristic. The circular slot with the smallest diameter is located at the side of port 1, and the diameter of the circular slot is increased as it goes toward port 2. The low pass characteristics of each circular slot are compared with the proposed wideband LPF. The final designed LPF was fabricated on FR4 substrate, and its characteristics were tested. The measured S11 characteristic was maintained at over -3.3 dB in the frequency range of 1.89-20.00 GHz band, whereas the S21 characteristic was less than -21.4 dB in the frequency range of 2.66-20.00 GHz.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2019.05a
• /
• pp.324-324
• /
• 2019

최근 급격한 기후변화 및 도시화로 인해 강우시 첨두유량이 증가하고, 도심 및 농촌지역에 비점오염원과 관련된 문제가 빈번하게 발생하고 있는 실정이다. 비점오염원에 대한 관리는 발생원 및 특성 파악이 어려운 특성으로 인해 관리가 미흡하며, 이에 따라 비점오염원 관리의 중요성이 커지고 있다. 각 토지이용별로 발생하는 비점오염원을 적절하게 관리하기 위해서는 유역별 비점오염원 발생특성에 대한 파악이 우선적으로 이루어져야 하며 다양한 관리기법에 대한 분석이 필요하다. 이에 본 연구에서는 SWAT모형을 이용하여 비점저감시설을 적용하였을 때의 비점오염부하량의 변화에 대한 분석을 진행하였다. 본 연구에서는 도시유역, 농업유역, 복합유역을 대상으로 비점저감시설을 적용하였을 때 비점오염부하량의 변화를 분석하였다. 우선 유역별 유출량 및 비점오염부하량을 모의하기 위하여 SWAT모델을 사용하였다. 모의된 유출량 및 비점오염부하량은 수질 측정 성과를 이용하여 보정을 수행하였다. 이후 비점오염 취약 소유역 선정을 위해 수질항목별 연간 비점오염부하량 크기에 따라 순위를 산정하고, 순위를 산술 평균하여 소유역별 전체 오염원에 대한 비점오염부하량 순위를 산정하였다. 비점오염 취약 소유역에 BMPs 및 LID를 적용한 결과, 도촌천의 비점오염 취약 소유역에서 SS, $NO_3-N$, TP의 평균 저감효율은 각각 11.17%, 3.47%, 18.85%로 나타났다. 공지천 도시지역에 LID 적용시 비점오염 취약 소유역에서 SS, $NO_3-N$, TP의 평균 저감효율은 각각 0.67%, 5.77%, 1.86%로 나타났다. 또한 공지천 농촌지역에 BMPs 적용시 SS, TN, TP의 평균 저감효율은 각각 14.22%, 1.67%, 4.43%로 나타났다. 또한 설성천의 비점오염 취약 소유역에서의 SS, TN, TP의 평균 저감효율은 각각 57.29%, 7.48%, 14.84%로 나타났다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.338-338
• /
• 2012

사파이어 ($Al_2O_3$)는 높은 밴드갭 에너지 (~19.5 eV)를 가진 물질로서 우수한 내마모성, 강도, 전기 절연성 및 안정한 화학적 특성을 갖고 발광다이오드 기판, 보석재료 등 각종 산업 및 기술적 분야에서 널리 사용되고 있다. 특히, 플립칩 발광다이오드 구조의 경우 광추출효율을 향상시키기 위해 높은 투과도를 갖는 사파이어 기판이 요구되어 왔으며, 지금까지 건식/습식식각방법을 이용한 사파이어 표면에 마이크로 크기의 심한 거칠기 또는 요철이 형성된 나노크기의 격자구조를 형성시키는 연구가 진행되어 오고 있다. 그 중, 나노 크기의 격자구조는 공기에서 반도체 기판까지 선형적인 유효굴절률 분포를 갖기 때문에 표면에서 생기는 Fresnel 반사 손실을 줄일 수 있다. 이러한 구조를 형성하기 위해서는 식각 마스크가 필요한데, 형성 방법으로 레이저 간섭 리소그래피, 전자빔 리소그래피, 나노임프린트 리소그래피 등이 있으나, 비싼 가격과 복잡한 공정 절차 등의 단점을 지니고 있다. 따라서 본 연구에서는 식각 마스크 패턴을 위해, 보다 저렴하고 간단한 실리카 나노구 및 열적응집 금 나노 입자를 이용하였다. 양면 폴리싱 c-plane 사파이어 기판을 사용하였고, 단일 층의 주기적인 실리카 나노구를 기판 표면에 스핀코팅에 의해 도포한 후 유도결합플라즈마 식각 장비를 이용하여 식각하여 주기적인 패턴을 갖는 렌즈모양의 격자구조를 형성하였다. 그리고 주기적으로 형성된 격자 위에 열 증착기를 이용하여 금 박막을 증착한 후 급속열적어닐닝(rapid thermal annealing)을 이용하여 열처리함으로써 비주기적인 금 나노입자를 형성시켰다. 형성된 금 나노패턴을 이용하여 동일한 조건으로 식각함으로써 광대역 및 전방향성 높은 투과도를 갖는 원뿔 모양의 사파이어 나노구조를 제작하였다. 제작된 샘플의 패턴 및 식각 형상은 전자현미경을 사용하여 관찰하였으며, UV-vis-NIR 분광광도계 (spectrophotometer)를 사용하여 투과율을 측정하였다. 렌즈 모양 표면 위에 원뿔모양의 나노구조를 갖는 사파이어 기판은 일반적인 사파이어 기판보다 향상된 투과율 특성을 보였다.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.10 no.3
• /
• pp.179-187
• /
• 2000

Fractal theory has strengths such as high compression rate and fast decoding time in application to image compression, but it suffers from long comparison time necessary for finding an optimally similar domain block in the encoding stage. This paper proposes a neural network based block classifier which enhances the encoding time significantly by classifying domain blocks into 4 patterns and searching only those blocks having the same pattern with the range block to be encoded. Size of a block is differently determined depending on the image complexity of the block. The proposed algorithm has been tested with three different images having various featrues. The experimental results have shown that the proposed algorithm enhances the compression time by 40% on average compared to the conventional fractal encoding algorithms, while maintaining allowable image qualify of PSNR 30 dB.