• 비파괴검사학회지
• /
• 제30권3호
• /
• pp.207-211
• /
• 2010

In this paper, the fluid AID(acoustic inspection device) was developed to measure SOS(speed of sound) since fluids used in most of industrial fields have different properties and its equipment is highly expensive. From AID developed, it is intended to get potentially the capability to distinguish the kind of fluid using the measurement by the SOS at various fields. In order to measure the sound speed of specific fluids, the measurement system and ultrasonic sensors are composed. The fluid used in the experimental work are soybean oil, glycerin, diesel oil and the error of time difference due to the container wall is extracted for preliminary experiment. As results, the variations of sound speed according to the temperature change of target fluid were analyzed and the polynomial equations were proposed.

• 한국정보통신학회논문지
• /
• 제11권2호
• /
• pp.265-272
• /
• 2007

본 논문은 비선형 휘도 출력을 요구하는 영상장치 기기를 위한 감마 보정에 관한 것이다. 제안된 감마 수정 시스템은 일반적인 공식에 의해 만들어지는 비선형적 특성을 지닌 감마 커브와 제안된 알고리즘에 의해 생성되는 결과와 차이를 최소화하기 위한 시스템이다. 오차를 최소하기 위해, 제안된 시스템은 Least Squares Polynomial을 사용하였다. 이 알고리즘은 샘플간의 점들에 대해서 최적의 다항식을 계산하는 방법이다. 각각의 시스템들은 연속적인 여러 개의 방정식으로 구성되어 있으며, 정밀도를 높이기 위해서 각 구간마다 고유의 중첩 구간을 가지고 있다. 최종적으로 알고리즘을 검증하여, 시스템들은 Verilog-HDL를 사용하여 구현되었다. 본 논문에선 가장 초기적 알고리즘인, Seed Table을 이용한 기존 시스템과 이를 개선하기 위해 만들어진 제안된 감마 시스템을 비교하려고 한다. 제안된 시스템과 기존 시스템은 클럭 대기(clock latency)가 1과 2의 값을 지닌다. 그러나 에러 범위(LSB)는 $0{\sim}+36$에서 $-1{\sim}+1$으로 향상되었다. 삼성 0.35 worst case 환경에서 합성된 gate count는 2,063에서 2,564으로 증가되었으나, maximum data arrival time은 29.05[ns]에서 17.52[ns]으로 더 빨라졌다.

• 대한의용생체공학회:의공학회지
• /
• 제32권3호
• /
• pp.245-250
• /
• 2011

Parallel imaging technique can provide several advantages for a multitude of MRI applications. Especially, in SENSE technique, sensitivity maps were always required in order to determine the reconstruction matrix, therefore, a number of difference approaches using sensitivity information from coils have been demonstrated to improve of image quality. Moreover, many filtering methods were proposed such as adaptive matched filter and nonlinear diffusion technique to optimize the suppression of background noise and to improve of image quality. In this study, we performed SENSE reconstruction using computer simulations to confirm the most suitable method for the feasibility of filtering effect and according to changing order of polynomial fit that were applied on variation of spatial resolution of sensitivity map. The image was obtained at 0.32T(Magfinder II, Genpia, Korea) MRI system using spin-echo pulse sequence(TR/TE = 500/20 ms, FOV = 300 mm, matrix = $128{\times}128$, thickness = 8 mm). For the simulation, obtained image was multiplied with four linear-array coil sensitivities which were formed of 2D-gaussian distribution and the image was complex white gaussian noise was added. Image processing was separated to apply two methods which were polynomial fitting and filtering according to spatial resolution of sensitivity map and each coil image was subsampled corresponding to reduction factor(r-factor) of 2 and 4. The results were compared to mean value of geomety factor(g-factor) and artifact power(AP) according to r-factor 2 and 4. Our results were represented while changing of spatial resolution of sensitivity map and r-factor, polynomial fit methods were represented the better results compared with general filtering methods. Although our result had limitation of computer simulation study instead of applying to experiment and coil geometric array such as linear, our method may be useful for determination of optimal sensitivity map in a linear coil array.

• 대한산업공학회지
• /
• 제30권1호
• /
• pp.27-35
• /
• 2004

A study was conducted to investigate an optimal vibration frequency for mobile phones with just noticeable difference(JND). The just noticeable difference, Weber's law, is the minimum amount by which stimulus intensity must be changed in order to produce a noticeable variation in sensory experience. In order to find the optimal vibration frequency, sixteen frequencies ranged from 24Hz to 603Hz were selected. Subjects then wereasked to differentiate a pair of vibration frequencies. For the analysis, the psychometric function to determine the optimal vibration frequency and the logistic regression to validate the determined frequency were used. The results show that the 2nd order polynomial equations were best fitted for the JND psychometric function and the optimal mobile phone vibrations were determined at 140Hz, 151 Hz, and 160Hz. With the ogive-shaped psychometric function developed by the logistic regression, the results of this study was validated that the determined vibration frequencies (140Hz, 151 Hz, and 160Hz) were optimal mobile phone vibration frequencies.

• Journal of the Optical Society of Korea
• /
• 제19권1호
• /
• pp.102-111
• /
• 2015

This paper proposes an algorithm for recovering the colors of objects from multiple near-infrared (near-IR) images. The International Commission on Illumination (CIE) color coordinates of objects are recovered from a series of gray images captured under multiple spectral near-IR illuminations using polynomial regression. The feasibility of the proposed algorithm is tested experimentally by using 24 color patches of the Color Rendition Chart. The experimental apparatus is composed of a monochrome digital camera without an IR cut-off filter and a custom-designed LED illuminator emitting multiple spectral near-IR illuminations, with peak wavelengths near the red edge of the visible band, namely at 700, 740, 780, and 860 nm. The average color difference between the original and the recovered colors for all 24 patches was found to be 11.1. However, if some particular patches with high value are disregarded, the average color difference is reduced to 4.2, and this value is within the acceptability tolerance for complex image on the display.

• 대한의용생체공학회:학술대회논문집
• /
• 대한의용생체공학회 1993년도 춘계학술대회
• /
• pp.38-41
• /
• 1993

For efficient transmission and storage of digital images, the requirements of image compression is incresing. Because the medical images contain diagnostic information small distortion has been more important factor than the low rate in such images. Generally the distortion in image is the difference of pixel values. However the image is percieved by human visual systems. So it is reasonable that human visual system characteristics be used as criteria of the image compression. In this paper, the Just Noticeable Difference curve is used as criteria of determining the homogeniety of a block and acceptibility of distortions. And Block Truncation Coding using spatial masking effect of eyes is adopted to code the blocks which contain line components. And small blocks which varies slowly can be approximated to polynomial functions successfully. We proposed the hybrid block coding scheme based on the block characteristics and human visual system characteristics. Simulation to several kinds of the medical images using this method showed that medical images can be compressed 5:1 - 10:1 without noticeable distortion.

• 한국기계가공학회지
• /
• 제13권6호
• /
• pp.88-98
• /
• 2014

A moving mass on a skewed linear guideway model to analyze the friction-induced stick-slip behavior of ball-screw-driven slides is proposed. To describe the friction force, a friction coefficient function is modelled as a third-order polynomial of the relative velocity between the slide mass and a guideway. A nonlinear differential equation of motion is derived and an approximate solution is obtained using a perturbation method for the amplitudes and base frequencies of both pure-slip and stick-slip oscillations. The results are presented with time responses, phase plots, and amplitude plots, which are compared adequately with those obtained by Runge Kutta 4th-order numerical integration, as long as the difference between the static and kinematic friction coefficients is small. However, errors in the results by the approximate solution increase and are not negligible if the difference between the friction coefficients exceeds approximately 40% of the static friction coefficient.

• Geomechanics and Engineering
• /
• 제25권3호
• /
• pp.221-231
• /
• 2021

A two dimensional model of linearly elastic soil spring used for the settlement analysis of the flexible mat foundation is suggested in this study. The spring constants of the soils underneath the foundation were modeled assuming uniformly vertical load applied onto the foundation. The soil spring constants were back calculated using the three-dimensional finite element analysis with Midas GTS NX program. Variation of the soil spring constants was modeled as a two-dimensional polynomial function in terms of the normalized spatial distances between the center of foundation and the analytical points. The Lysmer's analog spring for soils underneath the rigid foundation was adopted and calibrated for the flexible foundation. For validations, the newly proposed soil spring model was incorporated into a two dimensional finite difference analysis for a square mat foundation at the surface of an elastic half-space consisting of soft clays. Comparative study was made for elastic soils where the shear wave velocity is 120~180 m/s and the Poisson's ratio varies at 0.3~0.5. The resulting foundation settlements from the two dimensional finite difference analysis with the proposed soil springs were found in good agreement with those obtained directly from three dimensional finite element analyses. Details of the applications and limitations of the modified Lysmer's analog springs were discussed in this study.

• Current Optics and Photonics
• /
• 제7권5호
• /
• pp.518-528
• /
• 2023

As an effective means of remotely detecting the spectral information of the object, the spectral calibration for the Savart polarization interference imaging spectrometer (SPIIS) is a basis and prerequisite of information quantification, and its experimental calibration scheme is firstly proposed in this paper. In order to evaluate the accuracy of the spectral information acquisition, the linear interpolation, cubic spline interpolation, and piecewise cubic interpolation algorithms are adopted, and the precision of the quadratic polynomial fitting is the highest, whose fitting error is better than 5.8642 nm in the wavelength range of [500 nm, 820 nm]. Besides, the inversed value of the spectral resolution for the monochromatic light is greater than the theoretical value, and the deviation between them becomes larger with the wavelength increasing, which is mainly caused by the structural design of the SPIIS, together with the rationality of the spectral restoration algorithm and the selection of the maximum optical path difference (OPD). This work demonstrates that the SPIIS has achieved high performance assuring the feasibility of its practical use in various fields.

• 대한원격탐사학회지
• /
• 제30권4호
• /
• pp.505-510
• /
• 2014

NDVI는 기후변화 모니터링과 식생 변화 탐지 모니터링을 위한 주요한 지표이다. NDVI를 산출하기 전에 cloud masking, 대기보정과 같은 전처리 과정을 거침에도 불구하고 강수, 적설이나 구름의 영향이 완전히 제거되지 않아 NDVI가 현저히 낮게 관측되는 noise가 불규칙적으로 발생한다. 이러한 noise를 보정하기 위해서 국내외로 활발한 연구가 진행되고 있다. 기존의 다중 다항 회귀식을 이용한 방법에서는 과대추정이나 low peak를 잘 탐지하지 못하는 등 문제점이 나타나고 있으므로 보다 정확하게 noise를 보정하는 방법이 요구된다. 본 연구에서는 이동평균을 이용하여 noise를 보정하였고, 기존의 다중 다항 회귀식을 이용하여 산출한 NDVI 시계열과 비교를 해보았다. 그 결과 이동평균을 이용한 방법이 이전의 방법보다 NDVI noise를 잘 보정하는 것으로 보여진다.