• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회A
• /
• pp.1951-1956
• /
• 2008

Various MEMS accelerometers are used in engineering applications including automobiles, mobile phones, military systems, and electronic devices. Among them, the thermal accelerometer employing the temperature difference induced by the convective flow inside the micro cavity has been a topic of interest. As the convective sensor does not utilize a solid proof mass, it is compact, lightweight, inexpensive to manufacture, sensitive and highly endurable to mechanical shock. However, the complexity of the convective flow and various design constraints make optimization of a device a crucial step before fabrication. In this work, optimization of a 2-axis thermal convective MEMS accelerometer is conducted based on 3-dimensional numerical simulation. Parametric studies are performed by varying the several design variables such as the heater shape/size, the cavity size and types of the gas medium and the position of temperature probes in the sensor. The results of optimal design are presented.

• 전자공학회논문지B
• /
• 제31B권8호
• /
• pp.99-108
• /
• 1994

In this paper an image compression technique based on fractal theory using iterated contractive transformation is analysed and an improved image coder is suggested. Existing methods used the classifier proposed by Ramamurthi and Gersho which utilize the properties of neighboring pixels in the spatial domain. In this paper DCT-based classification is applied to 512$\times$512 images and PSNR improvement of 0.4~2.7 dB is obtained at lower bit rate over conventional algorithms. In addition the effect of varying the domain block size and quantization step size of the luminance shift parameter on the compression ratio and the image quality is compared and analysed.

• Bulletin of the Korean Chemical Society
• /
• 제24권3호
• /
• pp.299-305
• /
• 2003

Physical properties and microstructure of new coumarin 4 doped $SiO_2$-PDMS ORMOSILs, synthesized by one-step (OS, acid-catalysis) and two-step (TS, acid-base catalysis) routes of sol-gel method with varying pH (0.6 to 7) and dye content $(5\;{times}\;10^{-4}\;to\;5{\times}\;10^{-2}\;mole)$, are reported. BET, UV-visible spectroscopy and SEM were used for characterizations. The increase in acid or base concentration increased the size of pores and aggregated silica particles. The samples with pH ≤ 2.5 were transparent and attributed to the small size of pores (~20 Å) and silica particles. The samples with pH > 2.5 were translucent or opaque due to non-uniform pore system formed by voids and large aggregated silica particles. The surface area was found a key factor controlling the interactions between the gel matrix and the dye. The OS samples with the highest dye concentration exhibited the minimal values of pore size, surface area and silica particle size, resulting in the concentration-quenching phenomenon.

• 한국분말재료학회지
• /
• 제18권6호
• /
• pp.538-545
• /
• 2011

This study shows that catalytic activity of bimetallic RhPt nanoparticle arrays under CO oxidation can be tuned by varying the size and composition of nanoparticles. The tuning of size of RhPt nanoparticles was achieved by changing concentration of rhodium and platinum precursors in one-step polyol synthesis. Two-dimensional RhPt bimetallic nanoparticle arrays in different size and composition were prepared through Langmuir-Blodgett thin film technique. CO oxidation was carried out on these two-dimensional nanoparticle arrays, revealing higher activity on the smaller nanoparticles compared to the bigger nanoparticles. X-ray photoelectron spectroscopy (XPS) results indicate the preferential surface segregation of Rh compared to Pt on the smaller nanoparticles, which is consistent with the thermodynamic analysis. Because the catalytic activity is associated with differences in the rates of $O_2$ dissociative adsorption between Pt and Rh, this paper suppose that the surface segregation of Rh on the smaller bimetallic nanoparticles is responsible for the higher catalytic activity in CO oxidation. This result suggests a control mechanism of catalytic activity via synthetic approaches of colloid nanoparticles, with possible application in rational design of nanocatalysts.

• 대한전자공학회논문지TC
• /
• 제44권7호통권361호
• /
• pp.35-40
• /
• 2007

최근 이동통신 서비스가 광범위하게 사용되고 서비스 영역의 용이한 확대로 인하여 무선중계기에 대한 수요가 급격히 증가하고 있다. 그러나 무선중계기에는 중계된 전송 신호의 일부가 궤환되어 다시 수신안테나에 수신되는 궤환 간섭 신호가 발생한다. 궤환 간섭 신호의 제거에 이용하는 LMS (Least Mean Square) 알고리즘은 연산량이 적어 실시간으로 적용할 수 있지만, 필터 계수를 갱신에 일정한 스텝 사이즈(step size)를 사용하여 시변 채널과 같은 상황에서 성능이 저하된다. 이런 문제를 해결하기 위하여 본 논문에서는 궤환 간섭 제거기의 참조 입력 (reference input)과 에러 신호 사이에서 상관도를 구하여, 스텝 사이즈를 조정하는 새로운 가변 스텝 사이즈 LMS 알고리즘을 제안한다. 제안된 알고리즘을 WCDMA 무선 중계기에서 궤환 간섭 신호를 제거하는 필터에 적용하여 모의실험을 하였고, 기존의 간섭 제거 알고리즘과 비교하여 성능이 우수함을 확인할 수 있었다.

• Smart Structures and Systems
• /
• 제25권5호
• /
• pp.559-567
• /
• 2020

Vibration at the tip of various flexible manipulators may affect their operation accuracy and work efficiency. To suppress such vibrations, the feasibility of using MFC actuators and sensors is investigated in this paper. Considering the convergence of the famous filtered-x least mean square (FXLMS) algorithm could not be guaranteed while it is employed for vibration suppression of plants with varying secondary path, this paper proposes a new multiple model switching adaptive control algorithm to implement the real time active vibration suppression tests with a new multiple switching strategy. The new switching strategy is based on a cost function with reconstructed error signal and disturbance signal instead of the error signal from the error sensor. And from a robustness perspective, a new variable step-size sign algorithm (VSSA) based FXLMS algorithm is proposed to improve the convergence rate. A cantilever beam with varying tip mass is employed as flexible manipulator model. MFC layers are attached on both sides of it as sensors and actuators. A co-simulation platform was built using ADAMS and MATLAB to test the feasibility of the proposed algorithms. And an experimental platform was constructed to verify the effectiveness of MFC actuators and sensors and the real-time vibration control performance. Simulation and experiment results show that the proposed FXLMS algorithm based multiple model adaptive control approach has good convergence performance under varying load conditions for the flexible cantilever beam, and the proposed FX-VSSA-LMS algorithm based multiple model adaptive control algorithm has the best vibration suppression performance.

• 한국해안해양공학회지
• /
• 제14권2호
• /
• pp.116-127
• /
• 2002

대부분의 지진해일에 대한 수치모의는 천수방정식을 지배방정식으로 하고 leap-frog 유한차분기법을 주로 적용한다. 이 기법은 격자간격을 적절히 선정하면 분산효과를 옳게 고려할 수 있으나, 수심이 변하는 경우 전 계산영역에서 분산효과를 모두 만족시킬 수는 없다. 본 연구에서는 균일한 격자와 계산시간간격을 사용하면서도 수심이 완만하게 변하는 지형상을 전파하는 지진해일의 국부적인 분산관계를 만족시키기 위해 기존의 2차원 완 변수심상 분산보정 유한차분기법을 개선하고, 이 수치모형의 현장 적용성을 검증하기 위해 1983년 동해중부 지진해일을 검조기록이 있는 동해안의 속초, 묵호, 포항 그리고 울산항에 대하여 수치모의하였다. 또한 1983년 지진해일에 대해 각 항만에서 측정된 검조기록과 수치모의에 의해 계산된 값을 비교 분석하여 수치모형의 정밀도를 평가하였다.

• 한국해안해양공학회지
• /
• 제4권2호
• /
• pp.108-120
• /
• 1992

천수방정식의 유한 차분에 많이 이용되는 ADI 방법에 다른 Factorization 방법을 적용하여 각 방법에 의한 모형을 비교 검토하였다. 낙 모형을 해석해가 존재하는 선형 일차원 간제에 적용하여 수표, 저면마찰 및 시간간격에 따른 모형의 정확성을 분석하였다. 2차원 간제의 경우 선형 천수 방정식의 해석해를 구하여, 이 해석해와 각 모형의 수치 결과를 비교 검토하였다. 선형 천수 방정식의 경우 본 연구에서 제시한 ADI 방법이 기존 ADI 방법보다 정확하고 안정된 결과를 얻었다.

• 한국멀티미디어학회:학술대회논문집
• /
• 한국멀티미디어학회 2001년도 춘계학술발표논문집
• /
• pp.124-127
• /
• 2001

핸즈프리 음성 통신에 있어 음향 반향 제거 시스템은 필수적인 요소이다. 본 논문에서는 음향 반향을 효과적으로 제거하기 위한 새로운 시변 적응 상수를 갖는 적응 알고리즘을 제안한다. 제안하는 알고리즘은 최적 필터의 직교 원리를 이용하여 적응 알고리즘의 적응 상수를 시변한다. 직교 원리에 따라 적응 상수를 시변하면 적응 초기에는 적응 필터가 반향 경로를 추정하지 못해서 큰 값을 가지지만 수렴 후에는 적응 필터의 입력 신호와 추정 오차 신호간의 상호 상관도가 작아져서 정상 상태 오차가 작으며 근단화자 등 의 주변 잡음 신호에 적응필터 계수가 오조정되는 것을 줄일 수 있다. 본 논문에서 음향반향 시뮬레이션을 통해서 제안하는 적응 알고리즘이 기존의 방법에 비해서 우수함을 보인다.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2007년도 춘계 학술대회논문집
• /
• pp.177-181
• /
• 2007

Present study examines the numerical issues of cell structure simulation for various regimes of detonation phenomena ranging from weakly unstable to highly unstable detonations. Inviscid fluid dynamics equations with $variable-{\gamma}$ formulation and one-step Arrhenius reaction model are solved by a MUSCL-type TVD scheme and 4th order accurate Runge-Kutta time integration scheme. A series of numerical studies are carried out for the different regimes of the detonation phenomena to investigate the computational requirements for the simulation of the detonation wave cell structure by varying the reaction constants and grid resolutions. The computational results are investigated by comparing the solution of steady ZND structure to draw out the minimum grid resolutions and the size of the computational domain for the capturing cell structures of the different regimes of the detonation phenomena.