• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.12
• /
• pp.1091-1097
• /
• 2013

In this article, an advanced cooling surface based on micro-post arrays with non-homogeneous configurations is investigated and compared with conventional micro-post arrays with homogeneous configuration. The capillary performance of micro-post arrays are characterized using the capillary rate of rise experiments and numerical simulations which take into account the meniscus curvature. The experimental and numerical results show that that the capillary performance of the micro-post wick can be significantly enhanced, compared with the homogeneous type wick, by employing non-homogeneous configurations. The capillary performance is shown to be primarily a function of the solid fraction and increases linearly with decreasing solid fraction, regardless of the wick configuration, when the solid fraction is larger than 0.25. However, the capillary performance is found to be significantly reduced when the solid fraction falls below approximately 0.25.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.5
• /
• pp.89-93
• /
• 1995

To reduce the redundancy within samples that resulted from uniform sampling method, nonuniform sampling or nonredundant-sample coding methods can be considered. However, it is well known that when conventional nonuniform sampling methods are applied directly to speech signal, the required amount of data is comparable to or mure than that by uniform sampling method like PCM. To overcome this problem, a new nonuniform sampling method is proposed, in which nonuniform sampling is applied to the low-pass filtered speech signal and higher band is compensated by 8 colored Gaussian random noise with various noise levels. By this method, speech signal waveform can be encoded by 1.8 times larger compression ratio than the conventional nonuniform sampling method.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.25 no.2
• /
• pp.133-138
• /
• 2015

This paper presents a performance improvement of gray level co-occurrence matrix(GLCM) based on the nonuniform quantization, which is generally used to analyze the texture of images. The nonuniform quantization is given by Lloyd algorithm of recursive technique by minimizing the mean square error. The nonlinear intensity levels by performing nonuniformly the quantization of image have been used to decrease the dimension of GLCM, that is applied to reduce the computation loads as a results of generating the GLCM and calculating the texture parameters by using GLCM. The proposed method has been applied to 30 images of $120{\times}120$ pixels with 256-gray level for analyzing the texture by calculating the 6 parameters, such as angular second moment, contrast, variance, entropy, correlation, inverse difference moment. The experimental results show that the proposed method has a superior computation time and memory to the conventional 256-level GLCM method without performing the quantization. Especially, 16-gray level by using the nonuniform quantization has the superior performance for analyzing textures to another levels of 48, 32, 12, and 8 levels.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.4
• /
• pp.92-98
• /
• 2003

The optimum design of Hanyang low speed wind tunnel has been performed to augment flow uniformity and to reduce turbulence intensity of wind tunnel test section have to be known for reliability of wind tunnel test. The non-uniformity and turbulence intensity of Hanyang low speed wind tunnel were measured with Pilot tube and X-type hot-wire probe at various wind speeds. As the results, the non-uniformity decreases as the wind speed increases. The non-uniformity is relatively high in the proximity of the diffuser. The turbulence intensity is a little higher than design requirement in the middle of the test section.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.1
• /
• pp.61-67
• /
• 2018

The effects of subsurface inhomogeneities on the detection of buried metal pipes in ground-penetrating radar(GPR) signals are investigated numerically. To model the electrical properties of the subsurface inhomogeneities, the continuous random media(CRM) generation technique is introduced. For the electromagnetic simulation of GPR signals, the finite-difference time-domain(FDTD) method is implemented. As a function of the standard deviation and the correlation length of the relative permittivity distribution for a randomly inhomogeneous ground, the GPR signals of the buried metal pipes are compared using numerical simulations. As the subsurface inhomogeneities increase, the GPR signals of the buried pipes are distorted because of the effect of the subsurface clutter.

• The Korean Journal of Nuclear Medicine
• /
• v.32 no.1
• /
• pp.32-49
• /
• 1998

For estimation of regional myocardial blood flow with O-15 water PET, a few modifications considering partial volume effect based on single compartment model have been proposed. In this study, we attempted to quantify the degree of heterogeneity and to show the effect of tissue flow heterogeneity on partition coefficient(${\lambda}$) and to find the relation between perfusable tissue index(PTI) and ${\lambda}$ by computer simulation using two modified models. We simulated tissue curves for the regions with homogeneous and heterogeneous blood flow over a various flow range(0.2-4.0ml/g/min). Simulated heterogeneous tissue composed of 4 subregions of the same or different size of block which have different homogeneous flow and different degree of slope of distribution of blood flow. We measured the index representing heterogeneity of distribution of blood flow for each heterogeneous tissue by the constitution heterogeneity(CH). For model I, we assumed that tissue recovery coefficient ($F_{MME}$) was the product of partial volume effect($F_{MMF}$) and PTI. Using model I, PTI, flow, and $F_{MM}$ were estimated. For model II, we assumed that partition coefficient was another variable which could represent tissue characteristics of heterogeneity of flow distribution. Using model II, PTI, flow and ${\lambda}$ were estimated. For the simulated tissue with homogeneous flow, both models gave exactly the same estimates, of three parameters. For the simulated tissue with heterogeneous flow distribution, in model I, flow and $F_{MM}$ were correctly estimated as CH was increased moderately. In model II, flow and ${\lambda}$ were decreased curvi-linearly as CH was increased. The degree of underestimation of ${\lambda}$ obtained using model II, was correlated with CH. The degree of underestimation of flow was dependent on the degree of underestimation of ${\lambda}$. PTI was somewhat overestimated and did not change according to CH. We conclude that estimated ${\lambda}$ reflect the degree of tissue heterogeneity of flow distribution. We could use the degree of underestimation of ${\lambda}$ to find the characteristic heterogeneity of tissue flow and use ${\lambda}$ to recover the underestimated flow.

• Korean Journal of Food Science and Technology
• /
• v.36 no.1
• /
• pp.81-85
• /
• 2004

Quality characteristics of kochujang made with Aspergillus oryzae-and/or Cordyceps sp.-inoculated koji were investigated. Protease activity of Cordyceps sp.-inoculated koji was higher than that of A. oryzae-inoculated one. Sensory evaluation showed that kochujang made with mixture of A. oryzae-and Cordyceps sp.-inoculated koji (70 : 30, w/w) was superior to others.

• The Journal of the Acoustical Society of Korea
• /
• v.17 no.2
• /
• pp.32-42
• /
• 1998

본 논문은 비균일 분포 수동형 견인 배열 센서를 사용하여 입사각 추정은 물론, 도 플러 주파수를 동시에 추정해내기 위한 기법을 제안한다. 균일 선형 센서 배열을 사용하는 전통적인 수동형 견인 센서 배열 처리기법은 센서간의 등 간격 구조 및 단순한 표본 과정에 기인하여 활용 분야의 한계성을 가지며, 주된 응용 분야가 방사된 음향신호의 입사각을 추 정하는데만 국한되어 사용될 수 있다는 문제점을 내포하고 있다. 이러한 사실 때문에, 수중 천해 환경 하에서 견인함의 등속 이동에 의해 발생하는 도플러 주파수들에 대한 정보는 목 표물에 대한 식별이나 음향신호 전달 경로의 모델링에 중요한 매개변수로 작용하며, 일반적 인 수동형 견인 센서 배열의 사용에 의한 처리 방식으로는 이러한 매개변수의 추출이 불가 능하게 된다. 본 논문은 이러한 제한성을 극복하고 방사 신호들의 개별적인 입사각 및 도플 러 주파수의 동시 추정을 가능케하도록 비균일 분포의 선형 센서 배열과 Sample Skipping 기법(Sample Skipping Technique;SST)을 적용한 새로운 형태의 수동형 견인 배열 센서 처 리 기법을 제안한다.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2011.05a
• /
• pp.155-155
• /
• 2011

Dual coil을 사용하는 상용 AMAT DPS II 300 mm Centura 장비의 antenna의 전류비를 조절하여 $SiO_2$의 식각 균일도를 평가하였다. Inner turn과 outer turn의 흐르는 전류비를 분배 capacitor로 조절하여 16.9 %의 이온 전류 밀도 분포를 확인하였고, 투입 전력에 따라 200 W에서 12 %, 800 W에서 9 %로 점차 감소하는 경향을 확인하였다. 이때 300 mm wafer의 반지름 방향으로의 식각 균일도는 3 %로 측정되었고, FRC (flow ratio control)는 0.5에서 가장 균일한 결과를 얻었다.

• Proceedings of the Acoustical Society of Korea Conference
• /
• 1998.06e
• /
• pp.137-140
• /
• 1998

본 논문은 비균일 분포 수동형 견인 배열 센서를 사용하여 입사각 추정은 물론, 도플러 주파수를 동시에 추정해내기 위한 기법을 제안한다. 균일 선형 센서 배열을 사용하는 전통적인 수동형 견인 센서 배열 처리기법은 센서간의 등 간격구조 및 단순한 표본 과정에 기인하여 활용 분야의 한계성을 가지며, 주된 응용 분야가 방사된 음향신호의 입사각을 추정하는 데만 국한되어 사용될 수 있다는 문제점을 내포하고 있다. 본 논문은 이러한 제한성을 극복하고 방사 신호들의 개별적인 입사각 및 도플러 주파수의 동시 추정이 가능한 새로운 형태의 수동형 견인 배열 센서 처리 기법을 제안한다.