• Investigative Magnetic Resonance Imaging
• /
• 제5권1호
• /
• pp.38-42
• /
• 2001

2D TOF혈관조영술에서 presaturation RF펄스를 사용하여 정맥피에서 나오는 MR신호를 제거하고 얻은 동맥 angiogram에는 band형태로 동맥이 끊어져 나타나는 현상이 자주 보인다. 일부 동맥에서 피의 흐름은 한 심장 주기 동안에 3번의 펄스를 갖는데, 이 중 가운데 펄스는 짧은 기간 동안 역류를 한다. 이 역류하는 동맥피는 정맥피와 같은 방향이기 때문에 presaturation RF펄스에 의해 정맥피 처럼 saturation이 되어서 imaging slice로 흘러 들어가게 될 수 있다. 특히 이러한 경우가 phase encoding step의 dc 부근에서 발생하게 되면 그 때의 단면 영상에서 동맥이 강조가 될 수 없게 되어, 결과적으로 angiogram에는 그 단면을 지나는 동맥의 신호가 없어서 band 형태로 핏줄이 끊어져 나타나게 된다. Imaging slice와 saturation band와의 간격을 변화 시켜 가면서 angiogram을 얻어 봄으로서 이러한 현상을 실험적으로 확인하였다 나아가 saturation band를 rectangle형태에서 ramp 형태로 변경함으로써 이러한 artifacts를 제거 할 수 있는 방법을 제시하였다

• 한국과학교육학회지
• /
• 제28권3호
• /
• pp.187-196
• /
• 2008

In this study, a survey was conducted of students in grades 7 through 12, student teachers enrolled in their senior year at teachers' colleges, and science teachers. Subjects were surveyed on their conceptions of phenomenon related with dissolution, saturation, and extraction. The models and analogies used by student teachers and science teachers to explain dissolution were sought. The highest percentage of students thought of dissolution as a phenomenon in which particles broke into the spaces between other particles. The models or analogies used by the highest percentage of science teachers were similar. They generally conceived of dissolution phenomenon through what we call the 'space conception'. A conception of dissolution phenomenon as 'hydration through attraction of solvent and solute' was held by more student teachers than science teachers; there were some differences, however, according to their academic background. The percentage of teachers professing this view decreased when they attempted to explain the process of extraction of matter in a solution after other matter had dissolved or after the solution was cooled, indicating that the 'hydration' conception was not firmly established in the student teachers' cognition. Therefore, it can be inferred that the conceptions of dissolution as 'hydration' were transformed into the conceptions of dissolution as 'space' after teaching dissolution phenomenon as practicing teachers. This finding should be considered in teacher-training courses.

• 정보처리학회논문지B
• /
• 제14B권6호
• /
• pp.431-436
• /
• 2007

자기공명영상(Magnetic Resonance Imaging:MRI)은 물과 지방 사이에 화학적 이동 현상을 가지고 있고 지방에 의해 구조적 현상이 나타난다. 또한 지방은 기본적으로 강한 신호를 가지고 있어 잘못된 인공물을 형성한다. 그래서 지방소거(fat suppression)에 대해 연구하고자 한다. MRI에서 지방소거(fat suppression)방법만을 사용하여 진단하는데 약간의 어려움은 있지만 기본은 화학적 이동 선택 포화(chemical shift selective saturation : CHESS) pulse 방법을 이용하여 물과 지방 phantom을 가지고 지방소거(fat suppression)를 연구하는데 목적이 있다. 본 연구에서 CHESS pulse를 matlap 프로그램을 이용 Map pulse로 알맞게 design하고 Pre saturation을 하기 위한 pulse diagram이 가능하였고, fat phantom과 water phantom을 실험하여 지방소거 기법(fat saturation)의 효과를 볼 수가 있었으며 임상 적용 부위로 경추(C-SPINE), 요추(L-SPINE), 가습(BREAST)에 적용하여 의료영상진단에 있어 화학적 이동 선택 포화 CHESS pulse의 지방소거(fat suppression)는 유용한 방법임을 증명하였다.(충남대학병원 G.E 1.5T MR를 이용하여 실험하였다.)

• 방송공학회논문지
• /
• 제17권5호
• /
• pp.851-863
• /
• 2012

Retinex 기법은 영상의 어두운 영역의 가시성 향상을 통해 영상의 명암대비를 향상시킨다. 그러나 기존 Retinex 방식들은 RGB 색공간에서 수행되기 때문에 색상의 왜곡과 과다한 채도향상으로 인한 색신호 재현의 오류가 발생한다. 본 논문에서는 YCbCr 색공간에서 휘도신호에 대한 Retinex 처리를 통해 명암을 향상시키고, 휘도신호와 색상에 따른 최대 색차신호 테이블을 이용하여 휘도신호의 밝기 변화에 따라 변화된 채도를 밝기에 적응적으로 보정하는 방법을 제안한다. 제안된 방법은 과채도 현상을 막기 위해 휘도와 색상에 따른 채도의 상관관계를 고려하여 색차신호가 올바른 색역에 사상될 수 있도록 한다. 실험을 통해 제안된 방식은 기존 방식에 비해 다양한 특성을 갖는 영상에서 우수한 컬러 향상이 이루어짐을 확인하였다.

• Geomechanics and Engineering
• /
• 제23권1호
• /
• pp.85-92
• /
• 2020

This study adopted soil test and laboratory physical model experiments to simulate the tailings impoundment accumulation process according to the principle of similarity. Relying on the practical engineering, it analyzed the tailings deposition characteristics on dry beach surface during the damming process, as well as the variation rules of dam saturation line. Results suggested that, the tailings particles gradually became finer along the dry beach surface to inside the impoundment. The particle size suddenly changed at the junction between the deposited beach and the water surface, which displayed an obvious coarsening phenomenon. Besides, the deposited beach exhibited the vertical feature of coarse upward and fine downward on the whole. Additionally, in the physical model, the saturation line elevated with the increase in dam height, and its amplitude was relatively obvious within the range of 1.0-4.5 m away from the initial dam. Under flood condition, the saturation line height was higher than that under normal condition on the whole, with the maximum height difference of 4 cm. This study could provide an important theoretical basis for further studies on dam failure experiments and the evolution rules of leaked tailings flow.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
• /
• pp.211.2-211.2
• /
• 2015

In order to investigate the effect of front channel in DAL (dual active layer) TFT (thin film transistor), we successfully fabricated DAL TFT composed of ITZO and IGZO as active layer using the solution process. In this structure, ITZO and IGZO active layer were used as front and back channel, respectively. The front channel was changed from 0.05 to 0.2 M at fixed 0.3 M IGZO of back channel. When the mol concentration of front channel was increased, the threshold voltage (VTH) was increased from 2.0 to -11.9 V and off current also was increased from 10-12 to 10-11. This phenomenon is due to increasing the carrier concentration by increasing the volume of the front channel. The saturation mobility of DAL TFT with 0.05, 0.1, and 0.2 M ITZO were 0.45, 4.3, and $0.65cm2/V{\cdot}s$. Even though 0.2 M ITZO has higher carrier concentration than 0.05 and 0.1 M ITZO, the 0.1 M ITZO/0.3 M IGZO DAL TFT has the highest saturation mobility. This is due to channel defect such as pores and pin-holes. These defect sites were created during deposition process by solvent evaporation. Due to these defect sites, the 0.1 M ITZO/0.3 M IGZO DAL TFT shows the higher saturation mobility than that of DAL TFT with front channel of 0.2 M ITZO.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
• /
• pp.49-51
• /
• 2005

The saturation of transformer for short-circuit test suppress the peak current value during the test. And such phenomenon effect on the test results occasionally. This paper deals with the induction of the formula to restore the peak current value from the measured data.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
• /
• pp.853-858
• /
• 1993

The error back-propagation(BP) algorithm is widely used for finding optimum weights of multi-layer neural networks. However, the critical drawback of the BP algorithm is its slow convergence of error. The major reason for this slow convergence is the premature saturation which is a phenomenon that the error of a neural network stays almost constant for some period time during learning. An inappropriate selections of initial weights cause each neuron to be trapped in the premature saturation state, which brings in slow convergence speed of the multi-layer neural network. In this paper, to overcome the above problem, Micro-Genetic algorithms(.mu.-GAs) which can allow to find the near-optimal values, are used to select the proper weights and slopes of activation function of neurons. The effectiveness of the proposed algorithms will be demonstrated by some computer simulations of two d.o.f planar robot manipulator.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.491-494
• /
• 2002

To assess the electrostatic interaction of surfaces at the triple contact line, the electrostatic field is analyzed by using the finite element method. The Helmholtz free energy is used as a functional which should be minimized under an equilibrium condition. The numerical results are compared with the nonlinear analytical solution for a two-dimensional charged interface and linear solution for a wedge shaped geometry, which shows fairly good agreement. The method is applied to the analysis of electrostatic influence on the contact angle on a charged substrate. The excess free energy found to increase drastically as the contact angle approaches to zero. This excess free energy Plays an opposite role to the Primary electrocapillary effect, as the contact angle gets smaller. This enables an alternative explanation for the contact-angle saturation phenomenon occurring in electrical control of surface tension and contact angle.

• Nuclear Engineering and Technology
• /
• 제35권3호
• /
• pp.214-225
• /
• 2003

A teleoperated manipulator system has been developed for remote handling of the spent fuel bundles. A heavy-duty power manipulator with high reduction ratio joints is used for the slave manipulator in the developed system since the handling tasks of the spent fuel bundles need power. Also, the universal type master manipulator, which has force reflecting capability, is used for precise remote manipulation. The power manipulators so frequently occur the control input saturation that the precise control performances are not achieved due to the windup phenomenon. An advanced bilateral control scheme compensating for the saturation is applied to the teleoperated manipulator system. The validity of the developed system is verified by the grid cutting and fuel transportation tasks from the mockup spent fuel bundle.